The prevailing thought amongst the majority of the population is
that carbon dioxide (CO2) produced from the burning of fossil fuels is the lead factor in global warming. While I am not doubting that CO2 is a
greenhouse gas, I am somewhat unconvinced that it is as major a contributor to the effect as the press would have me believe.
Water, water, everywhere...
I find it peculiar that water vapour, a more potent greenhouse gas, is not receiving as much coverage in the press. According to the National Oceanic
and Atmospheric Administration (NOAA), water vapour is the most abundant greenhouse gas on the planet.
Greenhouse Gases - Frequently Asked Questions
As the temperature of the atmosphere rises, more water is evaporated from ground storage (rivers, oceans, reservoirs, soil). Because the air is
warmer, the relative humidity can be higher (in essence, the air is able to 'hold' more water when its warmer), leading to more water vapor in the
atmosphere. As a greenhouse gas, the higher concentration of water vapor is then able to absorb more thermal IR energy radiated from the Earth, thus
further warming the atmosphere. The warmer atmosphere can then hold more water vapor and so on and so on. This is referred to as a 'positive feedback
loop'. However, huge scientific uncertainty exists in defining the extent and importance of this feedback loop. As water vapor increases in the
atmosphere, more of it will eventually also condense into clouds, which are more able to reflect incoming solar radiation (thus allowing less energy
to reach the Earth's surface and heat it up).
Here is another article detailing the effects of water vapour in the atmosphere, but unfortunately it has too many terms I am not familiar with.
Perhaps someone else can explain it to me, and to the rest of ATS.
The climatic effects of water vapour
With that out of the way, let me continue by addressing the topic title.
Jet-setting our way to warmer climes
It cannot be denied that air travel by members of the public has increased over the past few decades. The advent of budget airlines has increased this
phenomena in order of magnitudes. But how is all this air travel affecting our planet? The most popular theories out there would argue that more
carbon dioxide is injected directly into the atmosphere with so many planes up in the sky. Water vapour is again conveniently ignored.
Dr Nicola Stuber published a study in the journal Nature
a theory proposing that water vapour from aircraft contrails can have a big impact on
global warming. As reported in National Geographic News:
Nicola Stuber, first author of the study, to be published in tomorrow's edition of the journal Nature, suggests that contrails' overall impact
on climate change is similar in scope to that of aircrafts' carbon dioxide (CO2) emissions over a hundred-year period.Please visit the link provided for the complete story.
Source: Airplane Contrails Boost Global Warming, Study Suggests
According to Stuber, the effect is most pronounced at night. While contrails block out sunlight during the day, it prevents heat from radiating off
into space at night. You could probably confirm this by observing the difference in the ambient temperature between cloudy and cloudless nights. To
combat this, Stuber proposes a reduction in the number of night time flights.
High-altitude atmospheric roasting planes
Another research on the other hand suggests that the warming effect from air travel is produced by contrails that form at high altitudes. The
researchers assert that contrails that form high in the sky form condensations that allow the heat from the sun to shine in but not radiate out.
High-altitude cirrus clouds, both natural and jet-induced, are unlike thicker low-altitude clouds, which block sunlight from reaching the surface.
The thinner cirrus, which float in the sky at 20,000 feet or higher, act like a see-through blanket - letting sunlight pass in, while trapping
Source: Longer Airline Flights Proposed to Combat Global Warming
Their proposed solution? Fly at lower altitudes. That may be easier said than done, however. Flying at lower heights consumes more fuel and time,
which could ultimately defeat the whole purpose of this exercise. Still, the scientists argue that the effect would be less damaging to the
Conclusion: contrails confound climatologist
There is still much we need to know about how water vapour affects the climate. It doesn't help that water vapour can create a feedback loop of
heating which creates more water vapour. In the final analysis, the jury is still out whether contrail formation effects global warming as
significantly as proposed by some studies. I myself am inclined to believe that it does. Cloud-cover and ambient temperature is something you can
observe by yourself, without the need for complex instruments. But perhaps a study conducted after the 9/11 attacks proved it best:
“September 11 – 14, 2001 had the biggest diurnal temperature range of any three-day period in the past 30 years,” said Andrew M.
Carleton. Not in three decades had there been such a large temperature spread between the daytime highs and the nighttime lows.
Source: Contrails: What’s Left Behind Is Bad News
The importance of the diurnal and annual cycle of air traffic for contrail
Water builds the heat in Europe
Global Warming Supercharged by Water Vapor?