Bloomberg BNA – Global temperatures will likely continue to rise in coming decades on track with higher estimates, despite a recent slowdown in the rate of global warming, according to a new study from a National Aeronautics and Space Administration scientist.
The study sought to reconcile different estimates for the Earth's climate sensitivity, or how temperatures change in response to changes in the atmosphere.
Some studies estimate low climate sensitivity, based on the assumption that global average temperatures would respond uniformly to increases of carbon dioxide and other greenhouse gas emissions. But the NASA study showed global temperatures are more sensitive to changes in aerosols and ozone in the atmosphere.
This higher sensitivity could mean a larger and faster temperature response, according to the study.
The study's findings could have “a really profound impact” on the amount of greenhouse gas emissions reductions needed for countries to meet an international goal of limiting temperature increases to 2 degrees Celsius (3.6 degrees Fahrenheit), the study's author, Drew Shindell, a climatologist at NASA's Goddard Institute for Space Studies in New York, told Bloomberg BNA.
“I wish it weren't so,” Shindell said in a statement March 11, “but forewarned is forearmed.”
Global temperatures have increased at a rate of 0.12 degree C (0.22 degree F) per decade since 1951, NASA said. But since 1998, the rate of warming has slowed to only 0.05 C (0.09 F) per decade—even as atmospheric carbon dioxide continues to rise.
IPCC Differs on Global Warming
Some recent research, including the latest report from the Intergovernmental Panel on Climate Change (IPCC), has suggested that the global warming slowdown means Earth may be less sensitive to greenhouse gas increases than previously thought. The IPCC estimated in September that global temperatures will rise by about 1.0 C (1.8 F) as the amount of carbon dioxide in the atmosphere gradually doubles.
But Shindell's research indicates the IPCC may be underestimating temperature changes. As carbon dioxide doubles, temperatures are most likely to rise 1.7 C (3.06 F) and are unlikely to be below 1.3 C (2.34 F), according to his study.
Shindell, who was a lead author for the IPCC's fifth assessment, said there was a lot of discussion of climate sensitivity within the IPCC “since it's so important to our future.”
The IPCC lowered its climate sensitivity estimate based on models that assumed air pollution was spread out evenly. But Shindell told Bloomberg BNA that he knew from previous studies that regional pollution can pack “a bigger bang for the buck.”
Northern Hemisphere's Influence Cited
Shindell's research showed that the climate is more sensitive to influences in the Northern Hemisphere, where most human-made aerosols are released and the vast majority of Earth's landmasses are located. Land responds more quickly to atmospheric changes than oceans.
The study was published March 9 in the journal Nature Climate Change.
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