Regional Responses to Black Carbon Aerosols: The Importance of Air-Sea Interaction

What is it about?

Particles of soot produced by combustion have greatly increased around the world over the last century and a half. As these particles absorb sunlight that might otherwise have been reflected back to space, they are believed to warm the planet as a whole. We tried to isolate the fingerprint of temperature change associated with soot (also known as black carbon) by taking a climate model and instantaneously increasing atmospheric concentrations from their 1860 values to modern values. The resulting pattern of temperature change looks very different than the pattern of atmospheric heating, with the largest warming found away from the most polluted regions and a region of cooling over the North Pacific. Changes in clouds, mixing, and ocean circulation all play a role in explaining these changes. In different regions these three processes have differing responses to the stabilization of the atmosphere produced by the additional heating at high altitudes. Over the North Pacific, the additional heating aloft reduces mixing of dry air into the near‐surface boundary layer and shades the surface, increasing relative humidity and allowing for more stratus clouds. Reduced evaporation causes the surface waters to freshen, slowing the overturning circulation that supplies warm water to this region.

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