Radiative forcing of climate by historical land cover change H. Damon Matthews, Andrew J. Weaver, Michael Eby, and Katrin J. Meissner Cory Martin Atmospheric Sciences

What is albedo? Ratio of radiation reflected by the surface to the total amount of incoming radiation Ratio of radiation reflected by the surface to the total amount of incoming radiation Bright objects have a high albedo Bright objects have a high albedo Dark objects have a low albedo Dark objects have a low albedo Dark – more absorption Dark – more absorption Bright – more reflection Bright – more reflection

Land Use and Climate Soil moisture capacity Soil moisture capacity Surface resistance to evaporation Surface resistance to evaporation Vegetation cover Vegetation cover Surface albedo Surface albedo Changes in albedo and evaporation lead to temperature changes Changes in albedo and evaporation lead to temperature changes

Methodology Model runs were compared to 300 years of climatological history Model runs were compared to 300 years of climatological history Multiple models used Multiple models used Ocean, sea-ice, moisture balance, and simple land model Ocean, sea-ice, moisture balance, and simple land model Each grid cell has one “dominant” vegetation type Each grid cell has one “dominant” vegetation type Seven types used Seven types used Dalton number Dalton number Albedo Albedo

Albedo and roughness Snow or sea-ice increases the surface albedo locally by 0.18

7 Model Runs Three 2000 year equilibrium runs Three 2000 year equilibrium runs 4 transient model runs 4 transient model runs Covering period from Covering period from

Cropland area

Equilibrium Runs 3 Runs, each simulating 2000 years 3 Runs, each simulating 2000 years 1 st - Land use same as present-day (most accurate) 1 st - Land use same as present-day (most accurate) 2 nd - Land use same as nd - Land use same as rd - Land use same as rd - Land use same as 1700 Each uses present-day CO2 levels and orbit Each uses present-day CO2 levels and orbit

Transient Runs Each begins with 1700-year pre-industrial run Each begins with 1700-year pre-industrial run 1700’s land cover 1700’s land cover 1700’s CO2 concentrations 1700’s CO2 concentrations 1700’s orbital position 1700’s orbital position 3 Runs and a control 3 Runs and a control Changing land-cover simulation Changing land-cover simulation Changing CO2 concentrations simulation Changing CO2 concentrations simulation Both land-cover and CO2 changes Both land-cover and CO2 changes

Results Equilibrium Results Equilibrium Results Transient Results Transient Results

Equilibrium Results

Cooling and less precipitation Cooling and less precipitation Much of the decrease in precipitation is most likely a result of the changing atmospheric temperature. Much of the decrease in precipitation is most likely a result of the changing atmospheric temperature. Tropics and subtropics Tropics and subtropics a larger roughness length results in more evaporation. a larger roughness length results in more evaporation run shows less cooling than present-day run 1992 run shows less cooling than present-day run

Transient Results

CO2 increase  Temp and precip increase CO2 increase  Temp and precip increase Land cover change  Temp and precip decrease Land cover change  Temp and precip decrease CO2 and land cover  Temp and precip increase but less than CO2 only run CO2 and land cover  Temp and precip increase but less than CO2 only run

Model Sensitivity Not all cropland is created equal Not all cropland is created equal Albedo of 0.17 is used but this only applies to some crops Albedo of 0.17 is used but this only applies to some crops Range 0.12 to 0.25 Range 0.12 to 0.25 Only rice <0.17 Only rice <0.17 Even more cooling when ran with an albedo of 0.20 instead of 0.17 for cropland Even more cooling when ran with an albedo of 0.20 instead of 0.17 for cropland

Conclusions “All model runs show a cooling associated with land cover change, both in global averages, and as amplified locally by positive feedbacks" “All model runs show a cooling associated with land cover change, both in global averages, and as amplified locally by positive feedbacks" Equilibrium Runs Equilibrium Runs Cooling of 0.10ºC to 0.22ºC Cooling of 0.10ºC to 0.22ºC Transient Runs Transient Runs Cooling of 0.09ºC to 0.17ºC Cooling of 0.09ºC to 0.17ºC

Conclusions / Future Work The transient model runs did not take into account the change in carbon sinks with the change of vegetation The transient model runs did not take into account the change in carbon sinks with the change of vegetation Some studies have shown that the warming due to the lower albedo of boreal forests equals the cooling caused by the carbon sequestration Some studies have shown that the warming due to the lower albedo of boreal forests equals the cooling caused by the carbon sequestration Authors want to see more research done on the effect on carbon sequestration by land cover change Authors want to see more research done on the effect on carbon sequestration by land cover change

Opinion Overall, I find the article convincing Overall, I find the article convincing Short, could’ve used more data Short, could’ve used more data Didn’t explain the processes simulated in the model runs as well as they should have Didn’t explain the processes simulated in the model runs as well as they should have I agree, more research needs to be done on carbon sequestration I agree, more research needs to be done on carbon sequestration

Questions?