PNNL

The Science

Soot particles absorb energy in the atmosphere and make snow and ice surfaces melt by reducing their ability to reflect sunlight. These changes influence atmospheric circulation patterns and amplify warming in the Arctic. Both greenhouse warming and natural particles in the air have been identified as factors that could influence El Niño/La Niña variability, but the impact of soot on El Niño frequency and magnitude has been left largely unexplored. A study led by scientists at the U.S. Department of Energy’s Pacific Northwest National Laboratory reveals the influence of Arctic and midlatitude black carbon—or soot particles—on the frequency of extreme El Niño-Southern Oscillation (ENSO) events. Researchers found that both Arctic and midlatitude soot can increase the frequency of extreme ENSO events by increasing sea surface temperature in the tropical Pacific. Increases in emissions of soot particles from the Northern Hemisphere midlatitudes and Arctic substantially warm the local atmosphere and oceans, weakening latitudinal temperature gradients that reduce the northward heat transport from the tropics.

The Impact

The findings from this study suggest that reducing Arctic and midlatitude soot emissions may have significant indirect consequences that affect the negative impact of tropical El Niño/La Niña extremes.

Summary

Researchers examined the response of atmospheric and oceanic variables associated with ENSO events to soot emissions from Arctic and midlatitude sources. They used the Community Earth System Model, a fully coupled global aerosol-climate model, to perform sensitivity experiments with substantially increased soot emissions from midlatitudes and the Arctic. They found that, in addition to local impacts on atmospheric and oceanic warming, increased soot emissions also reduce the northward heat transport from the tropics, leading to a sea surface warming in the tropical Pacific, where El Niño/La Niña occurs. Midlatitude soot emissions mainly affected the tropical atmosphere, while Arctic soot emissions causes more heat to accumulate in the ocean.

PNNL Contacts

Philip Rasch, Pacific Northwest National Laboratory, Philip.Rasch@pnnl.gov

Hailong Wang, Pacific Northwest National Laboratory, Hailong.Wang@pnnl.gov

Funding

This research is based on work that was supported by the U.S. Department of Energy (DOE) Office of Science, Biological and Environmental Research as part of the Regional and Global Climate Modeling program area. The National Energy Research Scientific Computing Center (NERSC), a DOE Office of Science user facility, provided computational support.