Anthropogenic Causes: Land Use & Land Cover Current Weather Finish Aerosols Changes in Surface Albedo and Land Cover Radiative Forcing of Land Cover Changes For Next Class: Read 10 (pp. 376-381)

Changes in Surface Albedo What is surface albedo and why is it important in the context of climate change? How have humans changed surface albedo? What other impacts do land use/land cover changes have on the climate system?

Changes in Surface Albedo Anthropogenic changes to the physical properties of the land surface can perturb the climate Directly exerting a radiative forcing Modifying other processes such as latent and sensible heat fluxes Large-scale character of vegetation can affect surface albedo Albedo of agricultural land can be very different from that of a natural landscape, especially forest Particular important when snow is present, as open land can be highly reflective with snow cover, while a forest is not

Albedo Figure 4.5

Human Activity and Climate Change Changes in land use and land cover Human development has transformed an estimated one-third to one-half of Earth’s land surfaces Changes can affect the vertical flux of heat and moisture influences where and when thunderstorms occur may modify atmospheric and oceanic circulation At middle latitudes, clearing of forests for agriculture and reforestation of abandoned farm land has caused regional climate change © AMS

Changes in Land Cover Since 1750 Cropland area expanded from 1750 to 1950 across Europe, Gangetic Plain, and in North America Since that time, croplands have been abandoned in Europe, North America and China, with an increase in forested areas Deforestation is occurring quite rapidly in the tropics How does deforestation (conversion of forest to grass) affect albedo, the surface energy balance, and RF?

Radiative Forcing of Land Cover Change Land cover change since 1850 has generally led to higher surface albedo and a slight negative radiative forcing Best estimate is -0.24 w m-2 However, spatial variability is quite high, with some areas showing no change in RF and other areas more negative than -5 w m-2 With tropical deforestation becoming more significant in recent decades, warming due to reduced evaporation may become more significant globally than increased albedo.

Black Carbon on Snow Presence of soot particles in snow causes a decrease of albedo and can affect snowmelt Best estimate of RF is +0.10 w m-2 http://www.arcticpeoples.org/

-0.15 w m-2 IPCC AR5

Anthropogenic Forcings on Climate Greenhouse gases Aerosols Land use/land cover change