From NASA Goddard: Tiny particles suspended in the air, known as aerosols, can darken snow and ice causing it to absorb more of the sun’s energy. But until recently, scientists rarely considered the effect of all three major types of light-absorbing aerosols together in climate models.
In a new study, NASA scientists used a climate model to examine the impact of this snow-darkening phenomenon on Northern Hemisphere snowpacks, including how it affects snow amount and heating on the ground in spring.
The study looked at three types of light-absorbing aerosols – dust, black carbon and organic carbon. Black carbon and organic carbon are produced from the burning of fossil fuels, like coal and oil, as well as biofuels and biomass, such as forests.
With their snow darkening effect added to NASA’s GEOS-5 climate model, scientists analyzed results from 2002 to 2011, and compared them to model runs done without the aerosols on snow. They found that the aerosols indeed played a role in absorbing more of the sun’s energy. Over broad places in the Northern Hemisphere, the darkened snow caused some surface temperatures to be up to 10 degrees Fahrenheit warmer than it would be if the snow were pristine. As a result, warmer, snow-darkened areas had less snow in spring than they would have had under pristine snow conditions.
According to the study, dust’s snow darkening effect significantly contributed to surface warming in Central Asia and the western Himalayas. Black carbon’s snow darkening effect had a larger impact primarily in Europe, the eastern Himalayas and East Asia. It had a smaller impact in North America. Organic carbon’s snow darkening effect was relatively lower but present in regions such as southeastern Siberia, northeastern East Asia and western Canada.
“As we add more of these aerosols to the mix, we are potentially increasing our overall impact on Earth’s climate,” said research scientist Teppei Yasunari at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.Impact of snow darkening via dust, black carbon, and organic carbon on boreal spring climate in the Earth system, Journal: Geophysical Research: Atmospheres.
Dust, black carbon (BC), and organic carbon (OC) aerosols, when deposited onto snow, are known to reduce the albedo of the snow (i.e., snow darkening effect (SDE)). Here using the NASA Goddard Earth Observing System Model, Version 5 (GEOS-5) with aerosol tracers and a state-of-the-art snow darkening module (GOddard SnoW Impurity Module: GOSWIM) for the land surface, we examine the role of SDE on climate in the boreal spring snowmelt season. SDE is found to produce significant surface warming (over 15 W m−2) over broad areas in midlatitudes, with dust being the most important contributor to the warming in central Asia and the western Himalayas and with BC having larger impact in the Europe, eastern Himalayas, East Asia, and North America. The contribution of OC to the warming is generally low but still significant mainly over southeastern Siberia, northeastern East Asia, and western Canada (~19% of the total solar visible absorption by these snow impurities). The simulations suggest that SDE strengthens the boreal spring water cycle in East Asia through water recycling and moisture advection from the ocean and contributes to the maintenance of dry conditions in parts of a region spanning Europe to central Asia, partially through feedback on the model’s background climatology. Overall, our study suggests that the existence of SDE in the Earth system associated with dust, BC, and OC contributes significantly to enhanced surface warming over continents in northern hemisphere midlatitudes during boreal spring, raising the surface skin temperature by approximately 3–6 K near the snowline.
h/t to WUWT reader “Parakoch”