1. 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 )

5. 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?

6. 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

7. Albedo
Figure 4.5

8. 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

9. 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?

11. 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 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.

12. Black Carbon on Snow
Presence of soot particles in snow causes a decrease of albedo and can affect snowmelt
Best estimate of RF is w m-2

13. -0.15 w m-2
IPCC AR5

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