Greenland ice core analysis shows drastic climate change near end of last ice age

Thanks for that. I think even though I am very new to ATS this is the first actual answer to any question I have asked, so thanks again

As to the thermal expansion bit, this is an actual response of water to heating. Thus if the global ocean temperature increases then the water must expand. This is a basic physical process which has been tested in the lab and measured and accurately modelled aswell. This is a well understood phenomena and must be taken into account when considering the sea level at any age in the past.

My personal view from the evidence which I have seen is that climate change is undeniable at the current moment. It will change the way that we have to live sometimes for the better for contries like the UK but for most of the third world contries life will get worse. Even this is a gross concept as people who live by the coast or on low lying areas will face greater impacts than me who lives inland on relatively high land. Whether this change in global climate is caused by humans is, I think, still an open question although I would lean heavily toward this. My only doubts are to whether this is just a natural occurence as all the previous episodes of rapid climate change have been.

OK that will do for now. Thanks

reply to post by Iggus


well, oceans' average depth is ~4000m iirc, and hypothetical warming warming is going to affect the surface, mostly. even ocean currents convey heat on the surface, think of the gulfstream, backflow happens only after cooling.

i wonder how you arrived at the conclusion that the tropics would suffer from warming. again, i suggest you read through the thread i linked in my last post, it contains a collection of sources with conflicting evidence.

thanks for responding! i didn't take into account the ice not yet in the sea. Thats cleared it up for me. Personally i think the damage has been done, we don't really have any control over mother nature

reply to post by Long Lance


The Gulf Stream does not technically influence the climate of europe it is actually the Northeast extension of the gulf stream which influences the climate of europe OK I am being pedantic. The Gulf Stream itself is just the western intesified boundary layer of the subtropical gyre in the Atlantic where-as the Northeast extension is after the gulf stream has seperated from the coast of America and is aided in its path by the Meridional Overturning Circulation (MOC). The MOC is what regulates the global climate as it is this that moves heat from the tropics to the poles and returns as deep ocean currents dense colder water. The key problem for the European climate would be if the MOC was to switch off, which would of course affect the Northeast extension of the Gulf Stream. This might occur if the dense water formation in the North Atlantic was to be reduced due to a reduction in ice formation which is a major part of dense water production. It is thought highly likely in fact that the MOC is driven by this dense water formation and the subsequent sinking of the water. It is also thought that this might have occured previously in history and created a cold period in European history called the younger dryas where an influx of water from a freshwater lake in America switched it off.

I know this hasn't answered you question exactly but I will try and get back to it, now I have to dash

reply to post by Iggus


what does any of this have to do with the general mechanism of ocean currents? or the heating of the bulk of seawater - which was iirc, the topic at hand.

it needs to cool to sink, most of the cooling happens along the way (shock?), there's probably a temperature threshold at which it'll be blocked or just dive a little later, after more surface cooling. But: who said it's going to be where the ice melts during summer months? that's merely an implicit assumption. volcanic activity alone could alter the course of currents, though.


at any rate, if the gulfstream stopped, even less vertical exchange would occur, at which point the depths of the oceans would be even less affected by surface temperatures.

[edit on 2008.6.27 by Long Lance]

reply to post by Long Lance


Firstly, you assume that current estimates of sea level rise attributed to thermal expansion are calculated by a crude approximation using the complete global ocean volume which is nonsense. Scientists really do have some idea what they are talking about most of the time and the calculated change in sea level accounts for varying temperature throughout the ocean system.

Secondly, I think you missed the point when it came to the Gulf Stream. The Gulf Stream is a large ocean current that is generated by two main factors.
The first is the wind patterns over the Atlantic ocean. There is a predominant wind pattern of easterlies and then westerlies over the sub tropical region moving from south to north. This sets up a circulation of surface waters around the Atlantic.
The second and just as important mechanism is sustaining the Gulf Stream is the change in coriolis parameter with latitude. This change in value has the effect of creating a large boundary current on the western side of the ocean basin. The same effect can be seen in all the worlds major ocean basins. The Gulf Stream then is an ocean current driven by the winds.

You mistake this for the North Atlantic current which extends from the end of the Gulf Stream, after it has separated from the American coast. The North Atlantic current is driven by density changes in the water and not by winds. Density changes within the water can occur either through temperature changes or through salinity changes. The density driven circulation patterns, otherwise known as the thermohaline circulation, play a pivitol role in determining the global climate.

You suggest that the sinking of the northward water would take place at some latitude whatever happens and that my suggestion that this is near the ice pack is nonsense. However, the formation of ice is one of the major driving factors in dense water formation and thus the sinking of this water and its conversion into North Atlantic Deep Water.
As ice is formed through freezing the water rejects the salt from it and puts it back into the ocean. This salty water eventually becomes so salty, and thus dense, that it sinks creating the dense water which drives the thermohaline circulation.

Why does the melting of the summer ice matter? Well when the ice melts it releases fresh water into the ocean system. This fresh water sits on top off all the water being brought up into the Arctic. This new water then cannot freeze and become ice because it has a blanket of fresh water over the top of it. The ice instead is reformed from this fresh water at the surface. This means that there is no brine rejection and thus no extra dense water formation to drive the thermohaline circulation. This could have devastating effects on the global climate.
This is not to say that the thermohaline circulation will cease but there will certainly be an effect upon the strength it.

Finally I said that this had happened before during the younger dryas period. A fresh water injection due to the retreat of the glaciers from North America led to a dramatic reduction in the thermohaline circulation. This led to a rapid change to very cold conditions.

It is for these complex reasons that I, and most scientists, don't use the term global warming but climate change. A warming of the atmosphere can have many strange effects upon a non-linear and highly complex system shuch as the global climate.

Originally posted by Iggus


You suggest that the sinking of the northward water would take place at some latitude whatever happens and that my suggestion that this is near the ice pack is nonsense. However, the formation of ice is one of the major driving factors in dense water formation and thus the sinking of this water and its conversion into North Atlantic Deep Water.
As ice is formed through freezing the water rejects the salt from it and puts it back into the ocean. This salty water eventually becomes so salty, and thus dense, that it sinks creating the dense water which drives the thermohaline circulation.

salt does seperate from water, but on a microscopic level. further seperation requires further mechanisms.

i have a link for you, which, as you'll see indicates freezing of any saline solution below -21°C

antoine.frostburg.edu...

since temps regularly drop below that threshold, salty ice is formed and fresh water ice forms mainly through precipitation.

i don't know where you're going with the gulfstream, it's just that without a back current, warm surface currents could not be maintained, because water does not 'pile up'. as long as the water cools enough it will descend and keep the current going. icy temperatures aren't even required, remember water's maximum density is at +4°C.

as for scienitst not averaging across the ocean's entire volume, heating even a few hundred feet by 1-2°C will not cause any flooding, the affected volume is dwarfed by the rest, see

www.guilford.edu...

and the expansion isn't that pronounced. iow, when the realm of speculation is left, catastrophic sea level rises dematerialize very quickly.

reply to post by Long Lance


With regards to the Gulf Stream, I am merely pointing out that the Gulf Stream itself is a WIND DRIVEN current and is part of the sub-tropical gyre in the Atlantic Ocean, see here for more info.

A return current at depth is involved in the DENSITY DRIVEN thermohaline circulation. This is driven by dense water sinking in the polar regions.

I will include this link to one of the worlds leading sea-ice specialists to explain how sea-ice does not form in exactly the same way as fresh water ice. Firstly, there is no density maximum at 4C in Arctic Sea water. If you want to have an in depth discussion on the formation and impacts of sea-ice I am more than happy to oblige, its one of my specialist subjects , but would probabley be better done elsewhere as it isn't really directly on topic.

The dense water which is assumed to drive the thermohaline circulation is North Atlantic Deep Water which has a temperature of between 2.2C and 3.5C and a salinity of between 34.9 and 34.97 parts per thousand. This water is not formed by just making the water colder but primarily by making it saltier.

This returns to the problem of putting a fresh water cap on the Arctic Ocean. The North Atlantic water flowing in to the Arctic would flow under this freshwater. Therefore it would not be frozen and would not have the significant brine increase within it. Thus it would not get dense enough to form North Atlantic Deep Water and thus couldn't sink to drive the circulation.

OK, I have no idea why I can't edit my Draft reply so I will do another post to finnish.

When it comes to thermal expansion rates of the ocean and the impact that they will have then I am afraid that I will have to stick with the results that are shown within internationally peer reviewed papers which use vast amounts of real world, and/or simulation, data and show their maths in full. If you wish to show you calculations exactly, rather than waving your hands and showing some single point representative plots, then maybe we could make headway. However, I fear that you will not do this and just disregard the work of those who have. If you can read their papers and show why they are wrong then do this and post a repsonse here or even better get it published so that the entire oceanographic scientific community can see why they are wrong.

OK maybe a little harsh but the point is that if you are going to question the work of others then do it with as much accuracy as they have used to presnt their ideas. It makes it much easier to discuss.

Originally posted by Iggus
OK maybe a little harsh but the point is that if you are going to question the work of others then do it with as much accuracy as they have used to presnt their ideas. It makes it much easier to discuss.

np and thanks for the link, btw.

what's wrong, well, as far as i can tell, the scale is. if you take typical thermal expansion coefficients of water into account and that only 100-200m are affected for the most part, the calculated rise is measured in cm only.

hypertextbook.com...

as can be found elsewhere, f-ex.

sedac.ciesin.org...

Our projections of greenhouse-gas induced sea-level rise due to thermal expansion between 1985 and 2 025 are also relatively small, 4-8 cm, accompanied by a global mean warming in the range 0.6-1.0°C. Estimating future changes in sea level therefore depends crucially on predicting the future melting of land-based glaciers and ice sheets, a daunting task.

let's see, even if the actual warming was 4C (by 2100), if linearity applies, the estimation reaches 32cm, well make that 40, because ß increases with temp. still, what's the fuss about? maybe it's because i'm a landrat, i just don't see the catastrophy.

i intended to comment on ocean curents again, but i figured i'd better avoid going off on tangents.

i read the article, though and appreciate it.

This does not apply to sea water. The addition of salt to the water lowers the temperature of maximum density, and once the salinity exceeds 24.7 parts per thousand (most Arctic surface water is 30-35), the temperature of maximum density disappears. Cooling of the ocean surface by a cold atmosphere will therefore always make the surface water more dense and will continue to cause convection right down to the freezing point - which itself is depressed by the addition of salt to about -1.8°C for typical sea water.

so, i stand corrected and the minimum for avg. sea water is at roughly -1.8C, at which point it starts to freeze.

PS: i know i shouldn't but how much of the ocean current has to freeze in order to noticably increase its salinity?

[edit on 2008.7.3 by Long Lance]

Only going to use quotes so that I can keep a track of all the post

Originally posted by Long Lance
what's wrong, well, as far as i can tell, the scale is. if you take typical thermal expansion coefficients of water into account and that only 100-200m are affected for the most part, the calculated rise is measured in cm only.

I will be a little pedantic here and say that this depth is only that which is affected directly by daily changes in surface temperature and is the surface mixed layer. The important bit is the permanent thermocline which is about 800m deep in the open ocean.

let's see, even if the actual warming was 4C (by 2100), if linearity applies, the estimation reaches 32cm, well make that 40, because ß increases with temp. still, what's the fuss about? maybe it's because i'm a landrat, i just don't see the catastrophy.

Now this we can agree on. The amount of sea-level rise is calculated at between 1.6mm and 3.3mm, which would lead to a rise over 40 years of between 7.4cm and 13.2cm which is what about you reported. This leads to about your sorts of numbers. These are in agreement with the IPCC report for sea level rise due to thermal expansion. (See here for a summary of and see page 4 for sea level rise contributions)

So I think that we actually agree on the amount of sea level rise due to thermal expansion. I guess we actually only differ on the effect this will have on the worlds population.

i read the article, though and appreciate it.

...snip...

so, i stand corrected and the minimum for avg. sea water is at roughly -1.8C, at which point it starts to freeze.

I will star your post simply for these lines. Actually reading someones answer seems to be something sorely missing from most posts I have seen so thanks for that. More impressively is to be willing to change your view when shown relevent facts. I definitely don't see this very often and actually feel that sometimes these things actually are about discussion to get at an answer, or at least more understanding (End of probabley patronisingly sounding bit)

PS: i know i shouldn't but how much of the ocean current has to freeze in order to noticably increase its salinity?

Your PS is a big question in itself. It depends where in the world you are and what the local conditions are like. Storfjorden, in Svalbaard, is a site of dense water production but is aided by a ridge keeping the water in so that it can get dense and then slowly flow out. It also depends on the other water masses below the freezing layer. If they are not that dense then the surface water will get denser than the lower layer and sink quickly, if there is a large density difference then the durface layer can get denser before it sinks.

Anyway I am just showing that I can't give you a direct answer and that the actual place of and volume of dense water production is an open question.

Thanks again for the reply