Weatherdem's Weblog

Bridging climate science, citizens, and policy

Carbon Dioxide & Clouds

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Do you know what the biggest problem with the 2007 IPCC Report is?  If you think it’s the largest conspiracy in the history of mankind, you’re in for quite a shock.  No, the biggest problem is that reality is far outpacing the assumptions made to construct the Report.  What do I mean?   I mean glaciers are melting faster, temperatures are rising faster, CO2 emissions are increasing faster, methane concentrations are rising faster, etc.  The assumptions made for the report that I’m aware of all underestimate the pace at which the climate system is changing.  And to be clear, I’m not bashing the report.  I’m concerned that the problem is growing and it’s not getting enough attention.

Case in point: a new study [subscrip. req’d] comes to the conclusion that when sea surface temperatures increase, low cloud cover decreases, letting in more sunlight.  More sunlight means more solar radiation hitting the same patch than before, increasing the temperature even more than before, etc.  That is what is called a positive feedback loop.  These kinds of loops are becoming more commonplace and more apparent to researchers as they delve further into the climate problem.

This feedback was investigated using two separate, independent datasets, a very encouraging sign, scientifically speaking.  Since they’re independent, they lend credence to the other.

This further ties into the IPCC Report’s use of climate models in this way: only one climate model was “particularly realistic” in modeling the cloud feedback.  Designated HadGEM1 (from the Hadley Center), the model warms the globe by 4.4°C when CO2 is doubled.  This compares to a median of 3.1°C warming for all of the models used in the Report.  This tells us that the IPCC must consider each model’s results more carefully in the future: they’re not all depicting realistic solutions.

Why is that important?  Remember I wrote above that CO2 emissions are rising faster than everybody predicted earlier this decade in preparation for this Report.  Without any change in our behavior, we’re headed toward more than three times the amount of CO2, much more than the doubling examined.  So how much more warming would result from that kind of CO2 forcing?  6°C or more?  For us Americans, that’s ~11°F.

Do you think we can handle an 11°F warmer world?  Do you think the world can handle an 11°F warming?  I don’t.  In addition to that, the next IPCC Report will begin considering the results of these studies.  The case for people’s influence on the climate will become more solid.  The forecasts of climate change will almost certainly become more dire.  We must do something about this now.

[h/t Climate Progress]

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