Smaller desert dust cooling effect estimated from analysis of dust size and abundance

TL;DR

This study refines estimates of desert dust's radiative effect, suggesting it may be less cooling or even warming the climate than previously thought, due to coarser dust particles than models assume.

Contribution

It provides new observational constraints on dust size and abundance, revising the estimated radiative effect of dust in climate models.

Findings

Dust aerosols are coarser than in models.

The dust radiative effect range is -0.48 to +0.20 W/m2.

Dust may cause net warming, not cooling.

Abstract

Desert dust aerosols affect Earth's global energy balance through direct interactions with radiation, and through indirect interactions with clouds and ecosystems. But the magnitudes of these effects are so uncertain that it remains unclear whether atmospheric dust has a net warming or cooling effect on global climate. Consequently, it is still uncertain whether large changes in atmospheric dust loading over the past century have slowed or accelerated anthropogenic climate change, or what the effects of potential future changes in dust loading will be. Here we present an analysis of the size and abundance of dust aerosols to constrain the direct radiative effect of dust. Using observational data on dust abundance, in situ measurements of dust optical properties and size distribution, and climate and atmospheric chemical transport model simulations of dust lifetime, we find that the dust found in the atmosphere is substantially coarser than represented in current global climate models. Since coarse dust warms climate, the global dust direct radiative effect is likely to be less cooling than the ~-0.4 W/m2 estimated by models in a current global aerosol model ensemble. Instead, we constrain the dust direct radiative effect to a range between -0.48 and +0.20 W/m2, which includes the possibility that dust causes a net warming of the planet.