Updated 1:30 p.m. EST, Friday, November 9
A new study of climate change software finds that those models which are most accurate in accounting for humidity also project higher temperature increases, up to above 7 degrees fahrenheit by the end of the 21st century.
The results of the study of 16 different leading climate models, published online Friday on the website of the journal Science, was performed by two scientists at the U.S. National Center for Atmospheric Research (NCAR), a collaborative, multi-institution climate research initiative that was launched out of the National Science Foundation 1960.
NCAR scientists John Fasullo and Kevin Trenberth analyzed the models, focusing on how accurate they were in representing the current, real-world distribution of relative humidity in the subtropics — regions of Earth that are mostly dry and desert-filled (from 10 to 30 degrees latitude from the equator).
The researchers compared the humidity levels of the subtropics regions in the models to data of those regions captured by two NASA satellite instruments — the Atmospheric Infrared Sounder (AIRS) on the Aqua satellite and Clouds and Earth’s Radiant Energy System (CERES), which is found on a few NASA satellites, as the agency noted in a press release. In fact, the entire study itself was funded by NASA.
After examining the satellite data and comparing it to humidity represented in the models, the scientists discovered that those models that were most accurate also were those which predicted higher temperature increases over the course of the century. The temperature increases of all 16 models ranged anywhere from 3 degrees fahrenheit to 8 degrees fahrenheit, with the leading models prior to this study indicating an average global temperature rise of 5 degrees fahrenheit.
“You can imagine New York becoming more like Richmond, VA under 3F of warming,” Fasullo wrote to TPM in an email. “Under 8F it would be more like Atlanta, GA. Of course this skirts the issue of the major adaptations that would have to occur with such changes and considerable impacts are likely as a result of such shifts.”
But now, according to Fasullo’s and Trenberth’s study, that should be revised up to over 7 degrees fahrenheit.
“Given how fundamental these processes are to clouds and the overall global climate, our findings indicate that warming is likely to be on the high side of current projections,” Fasullo said in a statement.
As a press release from NCAR notes: “The difference is important to reconcile, as a higher temperature rise would produce greater impacts on society in terms of sea level rise, heat waves, droughts, and other threats.”
That news is likely to be unwelcome to those especially affected by Hurricane Sandy on the East Coast and in the Tri-State area of New York, New Jersey and Connecticut. Politicians and climate writers all publicly claimed in the aftermath of that storm that it was likely worsened by climate change.
Specifically, the temperature increases in climate models are all forms of a common benchmark known as the equilibrium climate sensitivity (ECS), which gauges how much warmer the Earth becomes in a model once carbon dioxide emissions double over pre-industrial levels. At current emissions rates, that doubling will occur much sooner than 2100.
Further, the very humidity that the Fasullo and his researchers compared between the models and real life is also an important factor in global average surface temperature.
“In general, increases in temperature lead to decreases in relative humidity and clouds, though exceptions exist,” Fasullo explained to TPM. “Decreases in clouds lead to increases in the amount of sunlight absorbed by Earth and additional warming.”
In other words: As the Earth warms, it will likely become less humid and less cloudy and as a result, warmer still.
Here’s a graph from the University Corporation for Atmospheric Research, which manages the NCAR, showing all 16 climate models represented as stars, plotted against the ECS, carbon dioxide-caused temperature increase on the left and their relative humidity on the right. The brown column marked “observations” corresponds to the actual humidity measured at present by NASA satellites:
“The dry subtropics are a critical element in our future climate,” Fasullo added in a statement published by NCAR. “If we can better represent these regions in models, we can improve our predictions and provide society with a better sense of the impacts to expect in a warming world.”
Updated throughout to add further direct quotes and information from Fasullo.