NASA: Long-Term Global Warming Likely Despite Recent Warming Slowdown

Although the rate of global warming has slowed in recent years, the Earth will likely continue to warm in line with previous estimates, according to new NASA research.

According to Drew Shindell, a climatologist at NASA's Goddard Institute for Space Studies, the Earth will experience about 20 percent more warming than estimates that calculate warming based on global surface temperature observations taken in the past 150 years.

Shindell's observations, reported in the journal Nature Climate Change, hinge on a new and more detailed calculation of the sensitivity of Earth's climate to greenhouse gas emissions and other factors that cause it to change.

Since 1951, global temperatures have increased at a rate of 0.22 degrees Fahrenheit (0.12 degrees Celsius) per decade, but since 1998 the rate of warming has been more than cut in half, to 0.09°F (0.05°C) per decade. This comes even as the level of atmospheric carbon dioxide has risen at consistent levels throughout the decades.

"Some recent research, aimed at fine-tuning long-term warming projections by taking this slowdown into account, suggested Earth may be less sensitive to greenhouse gas increases than previously thought," NASA said in a statement, citing the recent Fifth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC), which agreed to lower range of Earth's potential for global warming.

Shindell's calculations focused on what's called Earth's "transient climate response," which determines how much global temperatures will change considering a 1 percent per yer atmospheric carbon dioxide increase. Carbon dioxide is the most significant greenhouse gas generated by humans.

The temperature change due to transient climate response has been calculated by a number of groups with a variety of results. Recent research pegs the temperature change at 2.52°F (1.4°C), while the IPCC's estimate is1.8°F (1.0°C).

Shindell contends that a transient climate response could be 3.06°F (1.7°C), goes on to predict that values will fall below 2.34°F (1.3°C).

Additionally, Shindell's calculations factored in variability of aerosols and how the airborne particles can affect climate change. Depending on their chemical makeup, some aerosols can cause warming effects, while others can cause a cooling effect. Previous research has shown that the Northern Hemisphere plays a greater role in transient climate response than the Southern Hemisphere, but the effect of aerosols on the equation was not deeply considered. These studies assumed a uniform impact from aerosols around the globe, but the Northern Hemisphere is the producer of the majority of aerosols.

The cooling effect of aerosols have have been underestimated in other reports, Shindell reports. He contends that when corrected, the range of likely warming based on surface temperature observations is in line, despite the recent slowdown in global temperature increases.

"Working on the IPCC, there was a lot of discussion of climate sensitivity since it's so important for our future," said Shindell, who was lead author of the IPCC Fifth Assessment Report's chapter on Anthropogenic and Natural Radiative Forcing.

"The conclusion was that the lower end of the expected warming range was smaller than we thought before," he said. "That was a big discussion. Yet, I kept thinking, we know the Northern Hemisphere has a disproportionate effect, and some pollutants are unevenly distributed. But we don't take that into account. I wanted to quantify how much the location mattered."