Some more climate change stuff; old records broken in some cases...

reply to post by 727Sky

Yes, warming changes established weather patterns. This will result in "time of year" records in both directions. However we are seeing more all time recorded highs and fewer all time recorded lows. If there was a cooling trend, don't you think it would be the opposite?

Local weather patterns will change. Warming will produce drier conditions in some locations and wetter conditions elsewhere. This will vary in both the large scale (subtropics getting drier, elswhere wetter) and on the smaller scale, being affected by terrain and other localized factors.

From your source:

The authors also find floods and heavy precipitation were more common during cold periods such as the Little Ice Age than during warm periods such as the Medieval Warm Period, the opposite of claims that warming increases precipitation and floods from increased atmospheric water vapor.

hockeyschtick.blogspot.com...

To point to the central Alps being drier during warm periods as evidence against the warming models is somewhat ridiculous, since the models predict exactly that situation. All of Europe is expected to see decreasing precipitation as warming continues.

reply to post by Phage


Maybe an apology is in order for a nonsensical reply, or at least a clarification.

More all time records regardless of what direction are essentially a meaningless metric to determine any kind of trend. Surface temperature has only been directly measured for 150years; the start of the global instrumental record falls within a period that was, in relation to the arbitrary set baseline, below 'normal'.

There was still a high chance to measure all time low temperatures in the first few years even though it was already the onset of a warming period. If the last two decades mark the peak of the recent period with above normal temperatures anomalies the chances are equally high to measure all time highs.

The number of records tell us very little in which direction the trends go and if humans had thermometers during any of the past warm or cold periods they would have measured the exact same thing at the peak of each period.

In addition, surface stations also measure strongly reduced convection in urbanized areas or any other aspect of the UHI or anomalous climate conditions (e.g. foehn effect).

And then there are roughly 1800years of climate change with humans without thermometers.
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Records all along

The first high resolution global scale paleoclimate-reconstruction has only been published this year, 2013. It's the first synthesis reconstruction with 30y resolution intervals for larger regions in the Southern Hemisphere and revised/reanalysed paleo-records of the Northern Hemisphere. It is by far the most comprehensive reconstrucion to date and it's still incomplete. Africa is excluded (the second largest continent), a palaeoceanographic analysis (for 70% of the global surface area) is still work in progress.

Proxy density for some areas is still sparse; there are still only single proxy-records for most continents; statistical analysis and proxy-contamination are still huge challenges to overcome and this is only scratching the surface in terms of inadequate scientific evidence still not advanced enough to draw final conclusions.

Paleo-climate research is in a steady flux, every few months a new study is published that in part or entirely contradicts earlier research. At least in this area of climate science there is no consensus, there can't be.

No climate scientist alive today could provide sufficient answers as to wether the Medieval Warm Period has been a global event, if there have been other protracted or short term warm periods similar to that of the last century or what exactly are the causes for the recent climate change. The two decades before the turn of the century have been kind of a 'dark age' for paleoclimatology, maybe it's a bit of an exaggeration, but if you look at the advances of the last two years alone it has some truth to it. Climate science is only beginning to fully understand what really drives the changes, what is cause and what is effect.

But in spite of all the inadequacies, some conclusions can be definitely drawn.

-Climate has always been highly variable, on a continental or even on a global scale. A steady state is an
arbitrary concept and inconsistent with all observations.

-Nature has always been and still is the dominant factor, nothing proves this better than the last 15years.

-The rates and magnitudes of change within the climate system as whole have been at times greater in the past or are comparable to the last two centuries.

-Compared to the instrumental observation of only 150 years, almost any region/continent for which
advanced temperature reconstructions exist, has experienced higher or lower temperature extremes in the past 2000years alone.

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PAGES and the globe

As mentioned above, although PAGES is the most comprehensive synthesis reconstruction there are still huge chunks missing which makes it impossible to fully compare it to the modern instrumental record.

Instrumental Temperatures





With regards to climate variability and records broken in the past, PAGES and similar advanced reconstructions are probably the closest we can get to finding a conclusive answer. It is clear form all 2000year long paleo-records that on all continents climate has always changed on all times scales (annual, multidecadal, centennial).








Continental-scale temperature variability during the past two millennia
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If the chances to set an all time temperature record depend on a particular climate regime or if a region experiences a warm or cold period then in the example of Europe and North America the probalility has been much higher or equally high a number of times in the past.

In Europe, slightly higher reconstructed temperatures were registered in A.D. 741–770, and the interval from A.D. 21–80 was substantially warmer than 1971–2000.

The high resolution of 30year intervals also shows high variability on multidecadal time scales.
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high Resolutions smaller Regions

Based on the PAGES reconstruction for the Arctic the study concludes that surface temperature were the warmest in last two centuries. Another high resolution recon with an extended proxy network for the Arctic-Atlantic region shows that only the upward trend during the transition from the LIA to the early twentieth-century warming period was the most pronounced in last 2000years.

Pairwise comparisons in the Arctic Atlantic Region

The most pronounced warming phase in our reconstruction occurred between 1900 and 1940, which is clearly seen in the measured meteorological records as well. In the instrumental record, positive SAT anomalies were largest in the Arctic Atlantic region during this period. This early twentieth-century warming (ETCW) has been subject to many studies, yet its reasons still defies full explanation.

Natural and anthropogenic (land-use, aerosols) forcings are believed to have contributed to the ETCW. According to Chylek et al. (2009), the Arctic warming from 1900 to 1940 proceeded at a significantly faster rate than the warming during the more recent decades and was highly correlated with the Atlantic Multi-decadal Oscillation (AMO) suggesting that the Arctic temperature variability is highly linked to the Atlantic Ocean thermohaline circulation at various temporal scales.

see next post

reply to post by Phage


more Records broken
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Orbital forcing of tree-ring data

The long-term trend now revealed in maximum latewood density data is in line with coupled general circulation models indicating albedo-driven feedback mechanisms and substantial summer cooling over the past two millennia in northern boreal and Arctic latitudes. These findings, together with the missing orbital signature in published dendrochronological records, suggest that large-scale nearsurface air-temperature reconstructions relying on treering data may underestimate pre-instrumental temperatures including warmth during Medieval and Roman times

N-scan shows a succession of warm and cold episodes including peak warmth during Roman and Medieval times alternating with severe cool conditions centred in the fourth and fourteenth centuries . Ad 21-50 (C1.05 °C, with respect to the 1951-1980 mean) was the warmest reconstructed 30-year period,~2 °C warmer than the coldest ad 1451-1480 period (􀀀-1.19 °C) and still 0.5 °C warmer than maximum twentieth-century warmth recorded ad 1921-1950 (0.52 °C). Twentieth-century Scandinavian warming is relatively small compared with most other Northern Hemisphere high-latitude regions.

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Medieval Global or not


If the more recent reconstructions are compared to earlier studies on which basis the MWP was declared to have been restricted to the Northern Hemisphere or was only a regional event, it can only be concluded that all available evidence is still wide open to any interpretation.

Based on what is known about the climate system today or what i know, even during major climate shifts the Northern and Southern Hemisphere have never changed simultaneously, the patterns of the recent change are no exception.

Reconstructions find the MWP

The extra-tropical Northern Hemisphere temperature in the last two millennia

The two-millennia long reconstruction shows a well defined Medieval Warm Period, with a peak warming ca. 950–1050AD reaching 0.6 C relative to the reference period 1880–1960 AD. The 500-yr long reconstruction confirms previous results obtained with the LOC method applied to a smaller proxy compilation; in particular it shows the Little Ice Age cumulating in 1580–1720AD with a temperature minimum of −1.0 C below the reference period.

The reconstructed local temperatures, the magnitude of which are subject to wide confidence intervals, show a rather geographically homogeneous Little Ice Age, while more geographical inhomogeneities are found for the Medieval Warm Period.

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China

Temperature changes over the past 2000 yr in China and comparison with the Northern Hemisphere

The warming during the 20th century is not unprecedented, as similar warming occurred during 981–1100 and 1201–1270, although the reconstructions for these intervals have uncertainties of ±0.28 to ±0.35°C at the 95% confidence level, respectively. The two coldest periods occurred during 1631–1690 and 1811–1870.

The difference between the minimum temperature in the LIA and the maximum temperature in the PWP is 0.65±0.13°C in the PLS reconstruction, and 0.55±0.16°C in the PCR reconstruction on a centennial timescale. The rate of warming between 1851 and 1950 is 0.88°C/100 yr in the PLS reconstruction and 0.92°C/100 yr in the PCR reconstruction, and this period represents a transition from the LIA to PWP.

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Indonesia -Indo-Pacific Warm Pool

New temperature reconstruction from Indo-Pacific warm pool

2,000- year-long temperature and hydrology reconstructions from the Indo-Pacific warm pool

"The more interesting and potentially controversial result is that our data indicate surface water temperatures during a part of the Medieval Warm Period that are similar to today's," says Oppo. NH temperature reconstructions also suggest that temperatures warmed during this time period between A.D. 1000 and A.D. 1250, but they were not as warm as modern temperatures. Oppo emphasizes, "Our results for this time period are really in stark contrast to the Northern Hemisphere reconstructions."

Reconstructed SST was, however, within error of modern values during the Medieval Warm Period from about AD 1000 to AD 1250, towards the end of the Medieval Warm Period. SSTs during the Little Ice Age (approximately ad 1550–1850) were variable, and 0.5 to 1 °C colder than modern values during the coldest intervals.

Reconstructed SSTs were warmest from AD 1000 to AD 1250 and during short periods of first millennium. Given the evidence that G. ruber tends to record near mean annual SSTs during warm intervals of the last 150 years, reconstructed SSTs during these warm periods probably reflect mean annual SSTs. If this is the case, as we suspect, then SSTs within error of modern SSTs occurred in the IPWP during the Medieval Warm Period and during brief periods of the first millennium AD.

If, on the other hand, G. ruber calcified preferentially during the JAS upwelling season throughout the study interval, then JAS SSTs as warm as modern also characterized the previous millennium. Regardless of G. ruber seasonality in this region, the reconstruction suggests that at least during the Medieval Warm Period, and possibly the preceding 1,000 years, Indonesian SSTs were similar to modern SSTs.

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In Summary.

On most continents old records are still not broken. Either cold or hot.

Global Mean Surface Temperatures are basically a meanigless statistic when compared to reconstructions of the past 2000 years. On a continental/regional scale nothing about the recent warm period is unprecedented.

Europe, North & South America, Antartica, the Atlantic-Arctic region, as a continental average have been at least once substantially warmer in last 2000 years alone.

Scandinavia, parts of the Mediterranean and Central Asia are not as warm today as they have been in the past.

A complete sophisticated global scale reconstruction where sea surface temperatures and most of the global land mass are included still doesn't exist.

Since this thread was meant to discuss the possibility of another cooling period in the next future, i will write a follow up post in the next days.

reply to post by talklikeapirat

-Climate has always been highly variable, on a continental or even on a global scale. A steady state is an arbitrary concept and inconsistent with all observations.

Has anyone claimed a steady state is the norm?

-Nature has always been and still is the dominant factor, nothing proves this better than the last 15years.

This conclusion cannot be drawn. There are, of course, natural factors which affect climate. Variations in volcanic activity, long term solar variation, long term orbital influences. Currently those factors are not in evidence. They cannot be correlated with the increasing temperatures we have seen.

-The rates and magnitudes of change within the climate system as whole have been at times greater in the past or are comparable to the last two centuries.

You have not provided evidence that the magnitude or rates have exceeded those of the past 100 years. But such evidence would not preclude human activity as the primary cause of the increase in temperatures which have been observed in the past 100 years.

-Compared to the instrumental observation of only 150 years, almost any region/continent for which
advanced temperature reconstructions exist, has experienced higher or lower temperature extremes in the past 2000years alone.

That statement cannot be categorically made. There is no proxy based data which can provide absolute temperature values.

If the chances to set an all time temperature record depend on a particular climate regime or if a region experiences a warm or cold period then in the example of Europe and North America the probalility has been much higher or equally high a number of times in the past.

That statistical analysis is based on 30 year periods. Current temperature records extend over more than 3 times that time span.

But, from that article:

According to this analysis, of the 323 individual proxy records that extend to ad 1500, more sites seem warmest during 1971–2000 than during any other 30-year period, both in terms of the total number of sites and their proportion in each region. Similarly, of the 52 individual records that extend to ad 500, more sites (and a higher proportion) seem warmest during the twentieth century than during any other century.

Based on what is known about the climate system today or what i know, even during major climate shifts the Northern and Southern Hemisphere have never changed simultaneously, the patterns of the recent change are no exception.

Temperatures records show an increasing frequency of high temperature records and a decreasing frequency of low temperature records. These records are not restricted by region/continent, they span all continents and both hemispheres.

Reconstructions find the MWP

Here is what that study says about the proxies for the period prior to 1500.

Of these proxies, 32 extend as far back as to the beginning of the first millennium. From these comprehensive proxy compilations we performed new reconstructions of the extra-tropical NH mean temperature. Note, however, that only little more than half of the proxies (the exact fraction depends on the calibration interval, etc.) correlate well enough with the local annual mean temperature to be included in the actual reconstructions.

So only 16 proxies are used for the MWP.

But does it actually say that temperatures were as warm as they are now? Nope.

The two-millennia long reconstruction shows a well defined Medieval Warm Period, with a peak warming ca. 950–1050AD reaching 0.6ºC relative to the reference period 1880–1960 AD.

The thing is, temperatures have been rising since 1960.

So was the world really as warm a thousand years ago as it is now? It doesn't seem that way.

“The Medieval Warm Period was not as uniformly warm as we once thought--we can start calling it the Medieval Period again,” said the study’s lead author, William D’Andrea, a climate scientist at Columbia University’s Lamont-Doherty Earth Observatory. “Our record indicates that recent summer temperatures on Svalbard are greater than even the warmest periods at that time.”

www.ldeo.columbia.edu...

www.geo.umass.edu...

On most continents old records are still not broken. Either cold or hot.

Incorrect. On all continents high temperature records have been broken.

Global Mean Surface Temperatures are basically a meanigless statistic when compared to reconstructions of the past 2000 years. On a continental/regional scale nothing about the recent warm period is unprecedented.

The large uncertainty of the reconstructions does not make it possible to make that statement definitively.

Europe, North & South America, Antartica, the Atlantic-Arctic region, as a continental average have been at least once substantially warmer in last 2000 years alone.

Substantially warmer than what? At best the reconstructions show temperatures equal to current. Reconstructions based on a limited sample of proxies for the period prior to 1500AD.

Scandinavia, parts of the Mediterranean and Central Asia are not as warm today as they have been in the past.

Continuous, high resolution reconstructions of Arctic temperatures shows that the current magnitude and rate of warming far exceeds any such changes in the past 18 centuries.

We find that the summer warmth of the past 50 yr recorded in both the instrumental and alkenone records was unmatched in West Spitsbergen in the course of the past 1800 yr, including during the Medieval Climate Anomaly, and that summers during the Little Ice Age (LIA) of the 18th and 19th centuries on Svalbard were not particularly cold, even though glaciers occupied their maximum Holocene extent.

www.geo.umass.edu...

reply to post by Phage

Has anyone claimed a steady state is the norm?

Absolutely, the idea of a quasi-steady state that only fluctuates within the bounds of natural variability is one of the basic tenets of the hypothesis that the climate would not have changed the way it did without human carbon emissions. You can rephrase or reformulate this argument in a number of ways. The premise of a steady state is fundamental to the concept, without a distinct definition for what would be normal an abnormal state could not be determined. This is not pure semantics. The basic premise is the assumption of normality.

A method to exemplify the divergence from an assumed normal state are model projections with different forcings.
In simple terms this is meant to show how the climate would behave without human influence.

You said it yourself.

Currently those factors are not in evidence. They cannot be correlated with the increasing temperatures we have seen.

You gotta be careful, you're awefully close to make an argument from ignorance.

This statement is wrong, it's probably best to clear up some misconceptions.

The IPCC proclaims with regards to second part of the last century that human influence was most likely the reason for the observed temperature increase since 1951, and they are 95% sure.

Global Mean Surface Temperatures were not increasing at all between the mid 40's and the late 1970's. A number of factors should have been supposedly responsible for the suppression of the temperature rise, while according to the hypothesis, the planet was already accumulating energy forced by human emissions.

IPCC SPM

WoodforTrees




On a global average, a distinct upward trend was observed from the early 1980's until the end of the century. This was the only period when temperatures were for the most part increasing uniformly. But even then large regions were either not warming at all or were cooling, the rise in some regions was more rapid than in others.

Large parts of the extra-tropical Pacific have not warmed at all or only show a slight upward trend in the last two decades at the end of the century. The same for parts of Northern and Southern Europe, while the arctic polar regions have warmed more rapidly, but also not uniformly and not as much as during the early 20th century. The Southern Ocean south of 60° has cooled in the same period. The list could go on.


This all has changed at the beginning of 21th century. Almost all trends (the averages for the Globe, Northern and Southern Hemisphere, the continents etc.) are either flat, slightly negative or cooling.

Some parts of North America are still warming others are not or are cooling, the trend for the continental average is zero.

Global Mean ST


The global tropics are cooling at a rate of roughly 0.14°C per decade, as can be seen it is still possible to measure temperature extremes that could potentially register as 'all time highs' although the mean trend is negative. (the spike is El Nino)

WoodforTrees is easy to use. You can look for yourself, so i don't have to post all the graphs here again. If you are familiar with a spreadsheet software you can create time series with the data sets provided by the Climate Explorer including the three global precipitation data sets, OHC and updated Sea Surface Temperatures. The data can be divided into logical subsets by selecting the coordinates for each grid and can be looked at more closely.

The thing is, temperatures have been rising since 1960.

Temperatures records show an increasing frequency of high temperature records and a decreasing frequency of low temperature records.

These two statements make absolutely no sense.

I will gladly adress all the other points you've made when we are on the same page how and when the planet was getting warmer.
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ETA. Before this comes up, least square trends are not affected by the choice of running averages (within limits) and are exclusively calculated from the source data.

reply to post by talklikeapirat

Absolutely, the idea of a quasi-steady state that only fluctuates within the bounds of natural variability is one of the basic tenets of the hypothesis that the climate would not have changed the way it did without human carbon emissions.

You seem to be flirting with a strawman argument. There is no denial that natural climate variation occurs. But yes, the change in climate seen in the past century is attributable to human activity.

The IPCC proclaims with regards to second part of the last century that human influence was most likely the reason for the observed temperature increase since 1951, and they are 95% sure.

Yes. And they also have very high confidence that humans have been causing warming for much longer than that.

The understanding of anthropogenic warming and cooling influences on climate has improved since the TAR, leading to very high confidence that the global average net effect of human activities since 1750 has been one of warming, w

It is very unlikely that climate changes of at least the seven centuries prior to 1950 were due to variability generated within the climate system alone. A significant fraction of the reconstructed Northern Hemisphere inter-decadal temperature variability over those centuries is very likely attributable to volcanic eruptions and changes in solar irradiance, and it is likely that anthropogenic forcing contributed to the early 20th-century warming evident in these records.

source

Global Mean Surface Temperatures were not increasing at all between the mid 40's and the late 1970's. A number of factors should have been supposedly responsible for the suppression of the temperature rise, while according to the hypothesis, the planet was already accumulating energy forced by human emissions.

But energy is not "accumulated" during periods of reduced forcing. And yes there are factors which reduce forcing; volcanic activity, phenomena like ENSO. But these are transient phenomena, they affect forcing while present but when they fade, forcing returns to positive levels. And, lets not forget anthropogenic causes for reducing forcing. Sulfur dioxide does not just come from volcanoes. www.atmos-chem-phys.net...

This all has changed at the beginning of 21th century. Almost all trends (the averages for the Globe, Northern and Southern Hemisphere, the continents etc.) are either flat, slightly negative or cooling.

Selecting a data range which supports your point is not considered a valid analysis, it is considered cherry picking. There is a warming trend. There have been periods when the rate declined (including 1900-1920) but the trend continued. The wider the period, the more clear the major trend becomes and the less significant the cherry picked, short term "trends". How can you say "it all changed"? You just presented an example of a flattening which lasted more than 30 years. Guess what? That short term "trend" didn't hold, did it?

These two statements make absolutely no sense.

Then perhaps you missed the context. The study you used to show that temperatures during the MWP were as high as they are now used the period 1880-1960 as the mean, not current temperatures. Temperatures have increased since 1960. It is warmer now than it was in 1960 and warmer than that MWP reconstruction shows.

Perhaps because you looked at the two statements as connected. There are more high temperature records being set and few low temperature records being set. That does not indicate that temperatures are decreasing.

reply to post by Phage

And yes there are factors which reduce forcing; volcanic activity, phenomena like ENSO.

Now you've officially joined the club.

Does ENSO reduce the entire 10-17 W/m2 extra forcing or is half of it volcano, transiently?

Think about if really want to be that guy.


Single Algae-Proxy based Analysis of ENSO Reverse Anti-Forcing on the transient Response of Volcanic Activity

Don't bother to reply

I still don't see how 400 parts per million of CO2 in the atmosphere can have so much effect on the rest of the gasses in the atmosphere, after all, 400 parts per million is less than one percent of the total atmosphere, and I was surprised to read an advert by an American manufacturing company that they made CO2 generators for greenhouse's!
That firm also makes large size water container for rainfall, I would think the preppers would like some of those!

reply to post by talklikeapirat

Don't bother to reply

Since you didn't really say anything and your link doesn't seem to have much to do with algae or forcing, there isn't much to reply to.

reply to post by pikestaff

I still don't see how 400 parts per million of CO2 in the atmosphere can have so much effect on the rest of the gasses in the atmosphere, after all, 400 parts per million is less than one percent of the total atmosphere

Try looking at it another way.

The two major gases in the atmosphere are nitrogen and oxygen. Together they make up 99% of air. There is also argon, at about 0.9%. These are not "greenhouse gases". They do not absorb infrared radiation. If there were no other gases in the atmosphere the Earth would be a much colder planet because the heat of the Sun would not be held in the atmosphere, much more of it would radiate into space.

So what does keep our atmosphere warm? The "greenhouse gases"; CO2 at 0.04%, methane at 0.0002%, and water vapor which varies depending on the location from 0.001% to 5% but in total makes up about 0.25%. There are a few others but their concentrations are extremely low. Our atmosphere is kept warm by the gasses that make up only 0.29% of the atmosphere.

So that small percentage of CO2 is actually 14% of the gases that warm the atmosphere.

“The Medieval Warm Period was not as uniformly warm as we once thought--we can start calling it the Medieval Period again,” said the study’s lead author, William D’Andrea, a climate scientist at Columbia University’s Lamont-Doherty Earth Observatory. “Our record indicates that recent summer temperatures on Svalbard are greater than even the warmest periods at that time.”

High-Arctic Heat Tops 1,800-Year High, Says Study - 2012

Thus, whether there really were warm episodes of global extent in Medieval times and how these compare with late 20th century temperature levels (especially those in the last 20 years of the 20th century) remains an intriguing question that deserves further scrutiny. Until a more extensive set of data is available, the absence of evidence does not necessarily imply evidence of absence.

Nevertheless, it must be stated that given the relatively limited evidence that does exist to support Lamb’soriginal contention (Lamb 1965), the burden of proof must rest on demonstrating that his concept of a MWE has validity, rather than trying to show that it does not.

The Climate of the Last Millennium - 2003




Science is an attempt to obtain the closest possible approximation to ‘truth’ by seeking information which contradicts existing understanding(s) and amending or rejecting existing understanding(s) in the light of obtained information.

Pseudoscience accepts an existing understanding as being ‘true’ then seeking information which supports the understanding while ignoring and/or rejecting information which contradicts existing understanding.
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The MWP

TEMPERATURE PROXY RECORDS COVERING THE LAST TWO MILLENNIA:
A TABULAR AND VISUAL OVERVIEW

Thus, the Medieval Warm Period and the Little Ice Age seem to have been as much a circum-North Pacific phenomenon as a circum-North Atlantic phenomenon. In fact, evidence of the Medieval Warm Period and the Little Ice Age is to be seen in places all around the world, such as the tropical Pacific Ocean, Central America, the Caribbean Sea, Ecuador and South Africa.

The period around AD 1000 seems, in many of the records, to have been the warmest in the past two millennia, whereas the 16th and 17th centuries seem to have been the coldest. In some records the 19th century is also a very cold century.

Northern Hemisphere

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Scandinavia

Variability and extremes of northern Scandinavian summer temperatures over the past two millennia - 2012

The record provides evidence for substantial warmth during Roman and Medieval times, larger in extent and longer in duration than 20th century warmth. The first century AD was the warmest 100-year period (+0.60°C on average relative to the 1951–1980 mean) of the Common Era, more than 1 °C warmer than the coldest 14th century AD(−0.51°C). The warmest and coldest reconstructed 30-year periods (AD 21–50 +1.05°C, and AD 1451–80 −1.19°C) differ by more than 2 °C, and the range between the five warmest and coldest reconstructed summers in the context of the past 2000 years is estimated to exceed 5°C.

Comparison of the new timeseries with five existing tree-ring based reconstructions from northern Scandinavia revealed synchronized climate fluctuations but substantially different absolute temperatures. Level offset among the various reconstructions in extremely cold and warm years (up to 3°C) and cold and warm 30-year periods (up to 1.5°C) are in the order of the total temperature variance of each individual reconstruction over the past 1500 to 2000 years.

Northern Europe/Arctic-Atlantic Region

A new reconstruction of temperature variability in the extra-tropical Northern Hemisphere during the last two millennia. - 2010

Our new two-millennia long extra-tropical Northern Hemisphere (90–30°N) temperature reconstruction supports a distinct Medieval Warm Period and an even more distinct Little Ice Age, followed by a rapid twentieth-century warming. We also find a pronounced Roman Warm Period and support for the Dark Age Cold Period. Our reconstruction is actually the first to show a Roman Warm Period as warm on a hemispheric scale as the twentieth century.

The amplitude of the reconstructed temperature variability on centennial time-scales exceeds 0.6°C and thus supports the conclusions of those previous reconstructions that have shown the largest low-frequency pre-industrial temperature variability. Substantial parts of the Roman Warm Period, from the first to the third centuries, and the Medieval Warm Period, from the ninth to the thirteenth centuries, seem to have equalled or exceeded the AD 1961–1990 mean temperature level in the extra-tropical Northern Hemisphere.

Since AD 1990, though, average temperatures in the extra-tropical Northern Hemisphere exceed those of any other warm decades the last two millennia, even the peak of the Medieval Warm Period, if we look at the instrumental temperature data spliced to the proxy reconstruction.

However, this sharp rise in temperature compared to the magnitude of warmth in previous warm periods should be cautiously interpreted since it is not visible in the proxy reconstruction itself.

European Alps

Multi-archive summer temperature reconstruction for the European Alps, AD 1053-1996

We present a multi-archive, multi-proxy summer temperature reconstruction for the European Alps covering the period AD 1053-1996 using tree-ring and lake sediment data. The new reconstruction is based on nine different calibration approaches and errors were estimated conservatively. Summer temperatures of the last millennium are characterised by two warm (AD 1053-1171 and 1823-1996) and two cold phases (AD 1172-1379 and 1573-1822).

Highest pre-industrial summer temperatures of the 12th century were 0.3°C warmer than the 20th century mean but 0.35°C colder than proxy derived temperatures at the end of the 20th century, though uncertainties during the early period of our reconstruction are likely increased due to reduced replication (number of individual measurement series) inherent to some of the proxy records used here. The lowest temperatures at the end of the 16th century were 1°C lower than the 20th century mean.

see post above

The MWP

Northern Hemisphere

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Iberian Peninsula

The Medieval Climate Anomaly in the Iberian Peninsula reconstructed from marine and lake records

Selected multi-proxy and accurately dated marine and terrestrial records covering the past 2000 years in the Iberian Peninsula (IP) facilitated a comprehensive regional paleoclimate reconstruction for the Medieval Climate Anomaly (MCA: 900-1300 AD). Most of the Iberian records indicate warm conditions during the MCA, in agreement with recent global paleoclimate reconstructions.

Climate variability during the last millennium has been attributed to fluctuations in solar irradiance and tropical volcanic eruptions, and the role of the NAO has recently been suggested to explain the differences in humidity among the MCA and the LIA. In fact, solar irradiance and the NAO are related, as indicated by recent global climate model experiments that shown how an increase (decrease) in solar irradiance can force a shift towards a high (low) NAO index.

North Atlantic

Late Holocene (0–2.4 ka BP) surface water temperature and salinity variability, Feni Drift, NE Atlantic Ocean - 2008

We presented one of the first high-resolution planktonic foraminiferal Mg/Ca and stable isotope records for the late Holocene of the high-latitude North Atlantic. As the core site is located along one of the main flow paths for northward advection of warm saline surface waters, inferred changes in surface water properties should largely reflect basin-scale ocean circulation changes, in turn affecting climate over the adjacent European continent.

On multicentennial timescales, our records are consistent with commonly assumed patterns of late Holocene climate variability, namely the so-called Roman and Medieval Warm Periods, Dark Ages cooling and Little Ice Age. However, none of these periods were uniformly warm or cold over several consecutive centuries, and the actual causes for this multicentennial variability remain elusive.

Eastern Mediterranean

Global climate instability re£ected by Eastern Mediterranean marine records during the late Holocene - 2001

During the last millennia at ca. 0.8 and 0.27 ka two climatic events occurred which are probably correlative to both the Medieval Warm Period and the cooling global event known as the Little Ice Age, respectively. A long-term slight increase in planktonic foraminiferal N18O values occurs together with a gradual decrease in the N13C values of both G. ruber and the benthic foraminifera Uvigerina mediterranea.

This trend is associated with an increase in sedimentation rates, Ti/Al ratio, magnetic susceptibility, and color index of the sediments. We suggest that this trend shown by various independent proxies seems to be related to the aridification process that started ca. 7.0 ka in the mid^low latitude desert belt and the SE Mediterranean region and continuous until the present.

Turkey

Winter-to-spring temperature dynamics in Turkey derived from tree rings since - 2013

We were able to develop a statistically robust, precisely dated and annually resolved chronology back to AD 1125. We proved that variability of δ13C in tree rings of J. excelsa is mainly dependent on winter-to-spring temperatures (January–May). Low-frequency trends, which were associated with the Medieval Warm Period and the Little Ice Age, were identified in the winter-to-spring temperature reconstruction, however, the twentieth century warming trend found elsewhere could not be identified in our proxy record, nor was it found in the corresponding meteorological data used for our study.

The Medieval Warm Period (MWP) is reflected by temperatures being constantly above the average between the early 12th and mid-14th century. Then temperatures decrease until 1700 with only a short increase around 1625. The little ice age (LIA) heralds itself by low values in the temperature reconstruction with the beginning of a decreasing temperature trend in 1475, and the LIA finally is in full swing during the 17th and 18th centuries, as indicted by very low reconstructed temperatures.

Sibiria

Environmental changes in the northern Altai during the last millennium - 2007

The pollen record from Lake Teletskoye is the first detailed climate and vegetation reconstruction for the last millennium inthe northern Altai Mountains. Dense Siberian pine forest dominated the area around the lake at least since ca. AD 1020. The climate conditions were similar to modern. Between AD 1100 and 1200, a short dry period with increased fire activity occurred. Around AD 1200, climate became more humid with the temperatures probably higher than today. This period of rather stable climate possibly reflecting Medieval Warm Epoch lasted until AD 1410.

Slightly drier climate conditions occurred between AD 1410 and 1560. A subsequent period with colder and more arid climate conditions between AD 1560 and 1820 is well correlated with the Little Ice Age. A climate warming inferred from the uppermost pollen spectra, accumulated after AD 1840, is consistent with the instrumental data from the Barnaul meteorological station.

see post above

The MWP

Northern Hemisphere

___________________________________________________________________________________________

Tibet

Solar influenced late Holocene temperature changes on the northern Tibetan Plateau - 2013

Considerable efforts have been made to extend temperature records beyond the instrumental period through proxy reconstructions, in order to further understand the mechanisms of past climate variability. Yet, the global coverage of existing temperature records is still limited, especially for some key regions like the Tibetan Plateau and for earlier times including the Medieval Warm Period (MWP).

Here we present decadally-resolved, alkenone-based,temperature records from two lakes on the northern Tibetan Plateau. Characterized by marked temperature variability, our records provide evidence that temperatures during the MWP were slightly higher than the modern period in this region. Further, our temperature reconstructions, within age uncertainty, can be well correlated with solar irradiance changes, suggesting a possible link between solar forcing and natural climate variability, at least on the northern Tibetan Plateau.

India

Tree ring imprints of long-term changes in climate in western Himalaya, India

Tree-ring analyses from semi-arid to arid regions in western Himalaya show immense potential for developing millennia long climate records. Millennium and longer ring-width chronologies of Himalayan pencil juniper (Juniperus polycarpos), Himalayan pencil cedar (Cedrus deodara) and Chilgoza pine (Pinus gerardiana) have been developed from different sites in western Himalaya. Studies conducted so far on various conifer species indicate strong precipitation signatures in ring-width measurement series.

The paucity of weather records from stations close to tree-ring sampling sites poses diffi culty in calibrating tree-ring data against climate data especially precipitation for its strong spatial variability in mountain regions.

However, for the existence of strong coherence in temperature, even in data from distant stations, more robust temperature reconstructions representing regional and hemispheric signatures have been developed. Tree-ring records from the region indicate multi-century warm and cool anomalies consistent with the Medieval Warm Period and Little Ice Age anomalies.

Pakistan

Impact of climate and CO2 on a millennium-long tree-ring carbon isotope record - 2009

While we find indications for warmth during the Medieval Warm Period (higher than today’s mean summer temperature), we also show that the low-frequency temperature pattern critically depends on the correction applied. Patterns of long-term climate variation, including the Medieval Warm Period, the Little Ice Age, and 20th century warmth are most similar to existing evidence when a strong influence of increased atmospheric CO2 on plant physiology is assumed.

Our reconstruction confirms much of the picture already known such as the existence of a MWP, cooler conditions during the LIA and warming towards the 20th century. This match broadly acts as a long-term validation for the correction factor derived from statistical comparisonsto instrumental data. Even though, due to lower sample depth, some care is needed in the interpretation of our data during the MWP, in turn, the reconstruction provides additional suggestions that High Asian temperatures during the MWP might have exceeded recent conditions. This finding is also hypothesized, but difficult to confirm with ringwidth data from living trees.

China/Tibet

Climate during the Medieval Climate Anomaly in China - 2011

Various climate archives reveal a heterogeneous occurrence of the Medieval Climate Anomaly in China in terms of timing, amplitude and duration. Uncertainty analyses indicate that it is difficult to assess whether the medieval warmth exceeded that of the late 20th century.Seen from a regional perspective, all four studied regions experienced warm periods within the 10th to 14th centuries.

However, the timing, duration and magnitudes of these warm periods vary substantiallyin each region and between regions. The maximal temperature in Central East China in the AD 1240s is ~0.8°C above the AD 1901-1950 average (due to the various regions from where reconstructions are available and the variable instrumental data availability, the period AD 1901-1950 has been selected as the common reference period for all areas).

The maximal temperatures are 0.4°C warmer in the 1190s for the Northeast and 0.2°C in the 1000s for the Tibet region. In the Northwest, the highest temperatures were reached in the 1100s. Finally, in the Northeast and Central East regions, the warm peaks during AD 900-1300 are higher than temperatures of the late 20th century.

China/Tibet

Amplitudes, rates, periodicities and causes of temperature variations in the past 2485 years and future trends over the central-eastern Tibetan Plateau

Amplitudes, rates, periodicities, causes and future trends of temperature variations based on tree rings for the past 2485 years on the central-eastern Tibetan Plateau were analyzed. The results showed that extreme climatic events on the Plateau, such as the Medieval Warm Period, Little Ice Age and 20th Century Warming appeared synchronously with those in other places worldwide. The largest amplitude and rate of temperature change occurred during the Eastern Jin Event (343–425 AD), and not in the late 20th century. There were significant cycles of 1324yrs, 800yr, 199yrs, 110yrs and 2–3yrs in the 2485-year temperature series.

The 1324yrs, 800yrs, 199yrs and 110yrs cycles are associated with solar activity, which greatly affects the Earth surface temperature. The long-term trends (>1000yr) of temperature were controlled by the millennium-scale cycle, and amplitudes were dominated by multi-century cycles. Moreover, cold intervals corresponded to sunspot minimums. The prediction indicated that the temperature will decrease in the future until to 2068 AD and then increase again.

see post above

The MWP

Northern Hemisphere/Tropics

___________________________________________________________________________________________


Japan

Clarifying springtime temperature reconstructions of the medieval period by gap-filling the cherry blossom phenological data series at Kyoto, Japan

We investigated documents and diaries from the 9th to l4th centuries to supplement the phenological data series of the flowering of Japanese chetry (Prunus jamasakura) in Kyoto, Japan, to improve and fill gaps in temperature estimates based on previously reported phenological data. We then reconstructed a nearly continuous series of March mean temperatures based on 224 years of chery flowering data, including 51 years of previously unused data, to clarify springtime climate changes.

We also attempted to estimate cherry full-flowering dates from phenological records of other deciduous species, adding further data for 6 years in the 10th and 11th centuries by using the flowering phenology of Japanese wisteria (Wisteria floribunda). The reconstructed 10th century March mean temperatures were around 7°C, indicating warmer conditions than at present. Temperatures then fell until the 1180s, recovered gradualty until the 1310s, and then declined again in the mid-14th century.

West Africa

Coherent High-and Low-Latitude Climate Variability During the Holocene Warm Period

High-resolution records of the last millennial-scale climate cycle spanning the MWP (occurring between 800 and 1300 A.D.) and the LIA (which occurred between 1300 and 1870 A.D.) from Greenland, the western North Atlantic, and the eastern subtropical North Atlantic (Hole 658C). The record of Greenland surfacetemperature variations was reconstructed from glacier borehole temperature data and documentstwo discrete LIA cooling events centered at 1500 and 1870 A.D.

Oxygen isotopic analyses of planktonic foraminifera in a well-dated, high-deposition-rate sediment core from the Bermuda Rise also document a twin-event, 1°C cooling signature of the LIA that was preceded by the MWP, which was about 1°C warmer.

At Hole 658C, the LIA cooling is also indicated by two distinct cooling events of 3° to 4°C amplitude between 1300 and 1850 A.D. the earlier MWP between 800 and 1200 A.D. was only marginally warmer than present. These results suggest that the most recent LIA-MWP climatic cycle occurred synchronously at these three locations within the dating uncertainties.

Western U.S./Tropical Pacific

Tropical Pacific – mid-latitude teleconnections in medieval time - 2007

Terrestrial and marine late Holocene proxy records from the western and central US suggest that climate between approximately 500 and 1350 A.D. was marked by generally arid conditions with episodes ofsevere centennial-scale drought, elevated incidence of wild fire, cool sea surface temperatures(SSTs) along the California coast, and dune mobilization in the western plains. This Medieval Climate Anomaly (MCA) was followed by wetter conditions and warming coastal SSTs during the transition into the “Little Ice Age” (LIA).

Proxy records from the tropical Pacific Ocean show contemporaneous changes indicating cool central and eastern tropical Pacific SSTs during the MCA, with warmer than modern temperatures in the western equatorial Pacific. This pattern of mid-latitude and tropical climate conditions is consistent with the hypothesis that the dry MCA in the western US resulted (at least in part) from tropically forced changes in winter NH circulation patterns like those associated with modern La Niña episodes.

Venezuela-Cariaco Basin

Generation, Transport, and Preservation of the Alkenone-Based U-37(K ') Sea Surface Temperature Index in the Water Column and Sediments of the Cariaco Basin (Venezuela)

The UK037 ratios of surface sediments indicate SST was higher (26.3°C) during the last 50 years of deposition than in the previous 300 years (25°C), signaling an upwelling decrease in the latter part of the twentieth century. The lowest UK037-derived temperatures relatively low alkenone fluxes, are consistent with conditions of enhanced upwelling, decreased SST and reduced haptophyte production.

The highest UK037-derived SST estimates (over 26.5°C) were measured during the Medieval Warm Period (MWP) and suggest reduced upwelling at this time. Prior to the MWP, the alkenone record indicates temperatures of 26°C. These compositions indicate stronger upwelling conditions during the Holocene relative to the last 50 years and the MWP but annual SSTs above those estimated for the LIA.

see post above

The MWP

Southern Hemisphere

___________________________________________________________________________________________


Chile/North

Late Holocene sea-surface temperature and precipitation variability in northern Patagonia

Climate changes occurring during the last two millennia are of particular importance for understanding recent and predicting future abrupt climate changes. The data presently available from this period shows that climate conditions were more variable than previously thought. During this interval, the so-called Medieval Warm Epoch, herein referred to as the Medieval Climatic Anomaly, and the Little Ice Age (LIA) are among the best known examples centennial-scale climate variability. Although these two periods were first identified in Europe and the Northern Hemisphere, growing evidence has shown a more widespread incidence, including bipolar connections.

However, most of the evidence regarding climate variability on this timescale still comes from records from the Northern Hemisphere; data for the middle and high latitudes of the Southern Hemisphere are still scarce. Deciphering climate variability the Southern Hemisphere and particularly from southern South America ― the only continental land mass lying between 38°S and the Antarctic Circle― is crucial for documenting the inter-hemispheric synchronicity of recent abrupt climate changes and thereby determining their ultimate cause(s).

Chile/South

A stable isotope case study of two lakes at Torres del Paine, southern Chile

The results indicate that at 1215 cal yr Bp the level of the lake was at 85 m a.s.l with a temperature close to 9.3°C, was at 82 m a.s.l. at 600 cal yr Bp with a temperature close to 8.5°C. This coincides with the timing ofthe Northern Hemisphere Medieval Warming Period. At 183 cal yr Bp the level of the lake was at 80 m a.s.l with a cooler temperature close to 7.7°C, representing a colder period coinciding with the timing of the Little Ice Age(LIA).

An interesting outcome of this study is that it reinforces the idea that the δ13C signal in carbonate deposits can be an effective tool in distinguishing between inorganic and biologically induced precipitation.

Chile/Central

High-resolution, quantitative climate reconstruction over the past 1000 years and pollution history derived from lake sediments in Central Chile

Our DJF temperature reconstruction suggest relatively mild summers from AD 860 to AD 1350 (-0.04 to +0.06°C wrt 20th century) that were interrupted by multi-decadal cooler periods AD 970 – 1040 (-0.40 to -0.51°C wrt 20th century) and AD 1080-1140 (0.48 to -0.63°C wrt 20th century).

The warmest period was found AD 1150-1350 (+0.27 to +0.37°C wrt 20th century). A sharp drop in DJF temperatures is observed between AD 1350 and AD 1400 (-0.3 °C / 10 yr, decadal trend) which was followed by constantly cool (-0.70 to -0.90°C wrt 20th century) summers until AD 1750.

After AD 1750 summer temperatures show higher variability at decadal scales until the beginning of the 20th century. Between AD 1750 and 1820 warm summers prevailed before summer temperature dropped again until AD 1880.

Southern Hemisphere/Australia, New Zealand, South America

Multiproxy summer and winter surface air temperature field reconstructions for southern South America covering the past centuries

Our summer temperature reconstructions suggest that a warm period extended in SSA from 900 (or even earlier) to the mid-fourteenth century. This is towards the end of the Medieval Climate Anomaly as concluded from NH temperature reconstructions, where most studies find a termination between ca. 1200–1350.The warm peaks between 900 and 1350 are distinct in SP, NP and CC with 30-year filtered anomalies of up to +0.9°C (wrt 1901–1995) in the late thirteenth and early fourteenth centuries. In these regions, the transition to colder conditions is characterized by two rapid temperature decreases between 1335 and 1355 as well as between 1370 and 1400.

The reconstructions of the ST region can be clearly distinguished from the other regions due to the weak warm anomalies before 1350 the absence of the distinct cool period at the beginning of the fifteenth century and the pronounced minimum around 1850 in summer.

reply to post by talklikeapirat

Let's look at what the authors of some of the articles you posted have to say about them:

Thus, whether there really were warm episodes of global extent in Medieval times and how these compare with late 20th century temperature levels (especially those in the last 20 years of the 20th century) remains an intriguing question that de-serves further scrutiny.

www.geo.umass.edu...
Bradley says that the studies they looked at do not show that the MWP was global in extent. Bradley says that the studies they looked at do not show that temperatures during the period equaled or exceeded current temperatures.

These records, however, differ by several degrees Celsius over the past two millennia, which appears huge if compared with the 20th Centu- ry warming signal in Scandinavia or elsewhere. We conclude that the temperature history of the last millennium is much less understood than often suggested, and that the regional and particularly the hemi-spheric scale pre-1400 temperature variance is largely unknown.

www.blogs.uni-mainz.de...
Esper says that the variation in results demonstrates that the methods used are inadequate to come to arrive at conclusions about the extent and magnitude of the MWP


You included this quote in your post:

Since AD 1990, though, average temperatures in the extra-tropical Northern Hemisphere exceed those of any other warm decades the last two millennia, even the peak of the Medieval Warm Period, if we look at the instrumental temperature data spliced to the proxy reconstruction.

www.agbjarn.blog.is...
Ljungquist says that northern hemisphere temperatures exceed those of the MWP, Based on observed temperatures and by applying reconstruction techniques. He cautions about the validity of these results which seems a bit odd since they are supplemented with actual temperature data.

Warmest summers 0.3º C warmer than the 20th century mean occurred between 1050 and 1200. These temperatures were, however, 0.35º lower than temperatures in the last decade of the 20th century, though uncertainties during the early period of our reconstruction are likely increased due to reduced replication (number of individual measurement series) inherent to some of the proxy records used here.

www.blogs.uni-mainz.de...
Traschel says that current summer time temperatures in the southern Alps have been higher than those during the early part of the 2nd millennium

The Medieval Climate Anomaly in the Iberian Peninsula reconstructed from marine and lake records

The reconstruction for the MCA, which suggests the presence of a warmer climate and relatively arid conditions in the Mediterranean Iberia but increased humidity on the Atlantic Ocean side of the peninsula, is consistent with a role for the NAO in having shaped the climate of the IP during the last millennium.

www.researchgate.net... e/32bfe5107925808f8d.pdf
This is more about precipitation than quantifying temperature anomalies. It links a strongly positive NAO to drier warmer weather in the Mediterranean. I find it interesting that the chart you posted shows that SSTs were much higher during the MWP than the present. It would seem that if modern warming were the result of the same forces which caused the MWP, we would see more similarity to ocean temperatures. Apparently the NAO is not influencing current climate as much as it did a thousand years ago.

Late Holocene (0–2.4 ka BP) surface water temperature and salinity variability, Feni Drift, NE Atlantic Ocean – 2008
Traces variables in the NE Atlantic. Nothing there really addresses the question of the extent of the MWP or the magnitude of the temperature anomaly. It does however, reference Mann and Jones, 2003. Here is that temperature reconstruction.


Global climate instability reflected by Eastern Mediterranean marine records during the late Holocene – 2001
Does not seem to provide any data on the magnitude of temperature anomalies. It says that climate has varied during the Holocene. We know that.

Winter-to-spring temperature dynamics in Turkey derived from tree rings since – 2013 It’s interesting to note that the temperatures early in the year (in Turkey) don’t seem to follow the overall warming trend over the past 100 years. That would seem to indicate that the MWP warming was the result of different influences, something different is happening that was happening in the past.


Environmental changes in the northern Altai during the last millennium – 2007
This article says that temperatures in the region were “probably” higher than today. It also extends the MWP about 200 years beyond what other proxies show.

Solar influenced late Holocene temperature changes on the northern Tibetan Plateau – 2013
This study used the same technique as that which show that modern temperatures in the Svalbard region are significantly higher than those during the MWP. Here is an interesting statement from the article.

In particular, despite inconsistent with the spatial patterns derived from climate model-assisted reconstructions, the substantially warmer condition on the northern Tibetan Plateau, together with the relatively warmer conditions on Greenland, the persistent positive North Atlantic Oscillation mode, negative Southern Oscillation Index and the prevailing La Niña-like conditions in the tropical Pacific, suggest anomalous climatic conditions during the MWP, beyond the climate variability captured by the recent warm period.

download.springer.com...
The warming during the MWP was different from the warming we’re seeing now. There were different climatic patterns. It seems that there is something else going on now to cause the warming.

Tree ring imprints of long-term changes in climate in western Himalaya, India

The temperature reconstructions from different regions in Himalaya show strong consistency. The late 20th century warming in western Himalaya, as reported in high-latitude northern Hemisphere, is subdued. This has been attributed partly to decrease in the strength of relationship between tree-ring-width chronologies and temperature records as well as decrease in mean temperature due to decreasing trend in minimum temperature in western Himalaya.

The correlation between tree ring proxies and temperatures seems to be declining. That would seem to indicate that something else might be going on. The downward trend in regional temperatures is also interesting. It seems to indicate that the Himalayas have enough of an influence on regional climate to buck the global trend. Not surprising that such a large mountain mass could do so.

cont.

Impact of climate and CO2 on a millennium-long tree-ring carbon isotope record – 2009
The authors say this about using their method for long term trends like the MWP.

Therefore, from our perspective, d 13 C tree-ring records are still strongly limited in contributing to the ongoing discussion on long-term frequencies and amplitudes of climate change over the past millennium, although they carry strong climate information in the high-frequency domain.

www.geo.uni-mainz.de...

Climate during the Medieval Climate Anomaly in China – 2011

On multidecadal to centennial timescales, several reconstructions show warming peaks that occurred during the period AD 900-1300, whereas their low confidence levels do not allow to assess whether the MCA has been warmer than the late 20th century.

Some proxies show it, some don’t. They can’t really tell if it was warmer then or not.

Multiproxy summer and winter surface air temperature field reconstructions for southern South America covering the past centuries

Along with forthcoming reconstructions of precipitation (Neukom et al. 2010 ) and sea level pres- sure, our results will help to understand the influence of globally relevant large scale patterns, such as ENSO, SAM and PDO on the climate of SSA as well as regional expressions of solar and volcanic forcings.

www.geo.umass.edu...

Quite the blitz you presented. I find the shotgun method distracting and generally not very productive, it gets in the way of detailed discussion. You didn't make any comment about the studies, don’t you think it makes sense to at least look at what each article actually says about its results?

At best the studies you presented show that, yes, there was a medieval warming. The timing of the warming in those regions show wide variation and there are conflicting studies. None of the studies can confidently claim that global average temperatures were higher then than now and many of them point out inconsistencies and problems found within their own analyses. They also often have problems reconciling differences seen when comparing proxies with observed modern temperature trends.

What we see in theses studies that oceanic and atmospheric patterns during the MWP were quite different than those seen in the modern era. I'll refer you to a statement I made previously about the global nature of the MWP.

But such evidence would not preclude human activity as the primary cause of the increase in temperatures which have been observed in the past 100 years.

Something different is going on now, something that was not going on during the MWP. Oceanic patterns don’t match. Atmospheric patterns don’t match. Solar influences don’t match. Orbital parameters don’t match. It seems this warming trend is quite different from the MWP and there are strong indications that human activity is the cause.

reply to post by Phage


Let's get something straight.


The only reason you've posted the Svalbard study plus the quote from the press release twice in this thread alone is because you thought it would support your pseudo-scientific argument that there has been no other time in recent history when the climate has changed in ways like we have seen in the last couple decades. And there is no consistency in your argument itself, you constantly switch positions in your attempt to make the facts fit your beliefs.


The single study you've posted in support for your claim that any past Global Warm Periods didn't really happen at all doesn't even deserve to be called scientific research. It was at best another curve-fitting exercise to produce a hockey stick. The same usual suspects and the same attempt to 'prove' global warming is unprecedented and man-made. The same annoying tone and attitude in the press release aimed at framing the debate. The endless repetition of the same old motivated reasoning that 'real scientists' have yet again found evidence that refutes the denier claims. There is nothing new here and each time the arguments are repeated more credibility is lost.


Your claim here (doesn't mean what you believe it does).

So only 16 proxies are used for the MWP.

If you're trying to argue that the number of proxies and the spatial distribution has any relevancy for the accuracy of the reconstruction, contemplate in a quiet moment why you've posted a study where only three proxies were used from a single site.

We could stop here.


In addition, every other single or multi-proxy reconstruction from the same area completely refutes the overconfident claims made by authors of the study, unsurprisingly.

Calibration of the two isotopic ice-core series from western Svalbard has enabled us to quantify the temporal evolution of past winter temperatures in Svalbard. The approximately millennial-scale reconstruction of the Longyearbyen DJF SAT can be conditionally partitioned into three major sub-periods.

The continuous winter temperature decline during the period of 800-
1800, with a magnitude of about 0.9°C century, was followed by the coldest century in Svalbard according to the reconstruction. The scale of the Little Ice Age-associated winter cooling was on the order of 4°C, as inferred from the comparison of the reconstructed and instrumental DJF temperatures for the two periods of the 1800s and 1900s.

The same procedure carried out for Vardø instrumental temperature series yielded a negative trend of magnitude 0.3 8C century1 before the 1800s and a Little Ice Age cooling of 1.3 8C on average in northern Norway. The rapid warming at the beginning of the 20th century is already well documented in the instrumental data and was accompanied by a parallel decline of sea-ice extent in the study area.

However, both the reconstructed DJF SAT as well as indirect indicators of summer temperatures suggest that the Medieval period was at least as warm as the end of the 1990s in Svalbard.

www.arcticcentre.org

Go back to the first of my MWP posts, pay attention this time and try to find out why i've included the Bradley paper, he's one of the co-authors of your Svalbard study.

Something different is going on now, something that was not going on during the MWP. Oceanic patterns don’t match. Atmospheric patterns don’t match. Solar influences don’t match. Orbital parameters don’t match. It seems this warming trend is quite different from the MWP and there are strong indications that human activity is the cause.

I have very little confindence left that you would have any idea wether or not something different is going on now. We both know you don't make these claims after a careful examination of all availble evidence. Everything i have seen so far is a classic display of confirmation bias, motivated reasoning and you jumping to conclusions. What makes you believe we could have a reasonable discussion that wouldn't end up with me having to respond to your circular logic?

The earth has been warming since the end of the last ice age 12,500 years ago.

During this warming there has been cycles of high warming and cooling.

As little as 5000 years ago lake lahontan in Nevada dried up and lost its climate effects over Nevada.

This happened in many parts of the world causing less lake cooling and dryer temperatures.

there is very little man caused global warming and a lot of natural warming from the last ice age.

If you look at the last 65 million years and the world temperatures and the plant and animal life is global warming really bad or will it help in the long run.

commons.wikimedia.org...:65_Myr_Climate_Change.png

I used to think global warming might be true until I started noticing all the documentaries made by NASA are never what was advertised the film would be about. Instead they are all about this global warming. All of them. Why is NASA so concerned in selling this and why must they keep cramming these phony testimonials into their films?

If fossil fuels are the problem then do something about that. Get rid of RDS. Encourage people to walk or cycle more

BTW how environmentally friendly is rocket fuel?