Research focused on the climate sensitivity of the atmosphere suggests recent ‘cooling’ spell could be a blip
Global temperatures are likely to increase in line with previous estimates, despite a recent slowdown in warming, says a new study by NASA.
Published in the journal Nature Climate Change, it suggests that calculations of how sensitive the climate is to levels of carbon dioxide did not account for the cooling effect of airborne particles.
Since 1998, the rate of warming has been only 0.09 F (0.05 C) per decade, down from 0.22 Fahrenheit (0.12 Celsius) since 1951, leading many to question whether climate change was a serious concern.
Drew Shindell, a climatologist at NASA’s Goddard Institute for Space Studies and lead author of the IPCC Fifth Assessment Report’s chapter on Anthropogenic and Natural Radiative Forcing, says the ‘cooling effect’ of aerosols and ozone has been underestimated.
According to Shindell, this means the earth could experience roughly 20% more warming than scientists calculated in the past.
While multiple studies have shown the Northern Hemisphere plays a stronger role than the Southern Hemisphere in transient climate change, this had not been included in calculations of the effect of atmospheric aerosols on climate sensitivity. Prior to Shindell’s work, such calculations had assumed aerosol impacts were uniform around the globe.
This difference means previous studies have underestimated the cooling effect of aerosols. When corrected, the range of likely warming based on surface temperature observations is in line with earlier estimates, despite the recent slowdown.
One reason for the disproportionate influence of the Northern Hemisphere, particularly as it pertains to the impact of aerosols, is that most man-made aerosols are released from the more industrialized regions north of the equator. Also, the vast majority of Earth’s landmasses are in the Northern Hemisphere.
This furthers the effect of the Northern Hemisphere because land, snow and ice adjust to atmospheric changes more quickly than the oceans of the world.
“Working on the IPCC, there was a lot of discussion of climate sensitivity since it’s so important for our future. The conclusion was that the lower end of the expected warming range was smaller than we thought before.
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.”