Transcript Eggenberger
Presented by: Audrey Eggenberger Geography: ASCS major Amazon Deforestation and Climate Change (1990) By: J. Shukla et. all
Combined Climate and Carbon-Cycle Effects of Large-Scale
Deforestation (2007) By: G. Bala et. all
Profile of the Amazon
Incredible biodiversity Important ozone sink Important role in global tropospheric chemistry Experiencing alarming rates of deforestation If nothing is changed, Amazon will disappear in 50 100 years
What do plants do?
Absorb and store CO 2 Act as H 2 O reservoir and heat reservoir Transpiration Reflect incoming solar radiation (SWdn) Albedo—fraction of SWdn reflected
Focus: Forests
Boreal Temperate Tropical Temperate Boreal
Vegetation and Climate
Traditionally vegetation type was thought to be a RESULT of local climate Complex experiments have shown, however, that the type of vegetation can influence regional climate Current climate and vegetation coexist in a dynamic equilibrium
Effects of Deforestation
Releases CO storage 2 stored in the living plants to atmosphere and eliminates future Alters physical properties of Earth’s surface Root system Water and heat storage Albedo
Climatological Implications
Warming influence from: Addition of CO2 greenhouse gas Decreased evapotranspiration (short run) Cooling influence from: Increased surface albedo Decreased evapotranspiration (long run) Greenhouse Effect Albedo Effect
It’s Complicated…
Dynamic equilibrium Complex interactions Teleconnection and Feedback problem Models are unable to solve this problem in foreseeable future There are local variations too Subgrid-Scale Problem
Amazon Deforestation and Climate Change
Shukla et. all Area of interest Investigates the effects of deforestation on the local physical climate system Uses a coupled numerical model of global atmosphere and biosphere Control Case: forest intact Deforestation Case: forest cover is replaced by degraded pasture
Experiment
Coupled model was integrated for 1 year for both the Control and Deforestation cases Only change from Control to Deforestation case was the replacement of forest with pasture (grass) Integrations were carried out for 12.5 months, starting from December 15 th
Results
Surface/soil temp (T s ) warmer Consistent with reduction in evapotranspiration (E) More Lwup (Ln) Higher albedo (a), leads to reduction of absorbed SWdn Reduced moisture and heat storage capacity Recall: B=SH/LH
Results cont.
Control case Deforestation case Reduction in evapotrans piration by 49.6 cm annually Reduction in precipitation by 64.2 cm annually
Bottom Line…
Rise in surface temperature locally Significant decrease in precipitation Precip decrease is larger than the reduction in evapotranspiration Moisture flux decreases as a whole Longer dry season Makes reclamation by rainforest highly unlikely Valuable ecosystem disrupted, if not devastated
Combined Climate and Carbon-Cycle Effects of Large Scale Deforestation
Bala et. all Investigates global effects of deforestation on climate Uses 3-D coupled global carbon-cycle and climate model Lawrence Livermore National Lab Integrated Climate and Carbon (INCCA) Model Vegetation, land, ocean
Experiment
6 different model runs (from year 2000-2150): 1.
2.
3.
4.
5.
6.
Control—no CO2 or deforestation Standard—no deforestation Tropical—deforestation in tropics only Temperate—deforestation in mid-latitudes Boreal—deforestation in boreal zones Global—deforestation EVERYWHERE
Results
In Global Case (compared to Standard): Atmospheric CO 2 content higher More ocean uptake of CO 2
Annual mean temperature
COOLER (by ~0.3K)
Cooling? Wait…what?!
It’s all thanks to our good friend, albedo Albedo increases for all forest domains More SWdn reflected globally Decrease in evapotranspiration also helps Smaller Heat reservoir
A Closer Look: Tropics
(Includes SH mid-latitudes)
Raised albedo = more reflected SWdn Less moisture= fewer clouds, greater sunlight penetration Raised CO 2 levels = warming RESULT: Slight cooling(~0.3K) Simulated spatial
temperature difference relative to Standard
case centered on year 2100 for tropical deforestation.
Temperate Zone
Raised albedo = more reflected SWdn Raised CO 2 levels = warming Clouds are not important factor RESULT: Cooling (~1.6K) Simulated spatial
temperature difference relative to Standard
case centered on year 2100 for temperate zone deforestation.
Boreal Zone
Simulated spatial
temperature difference relative to Standard
case centered on year 2100 for boreal zone deforestation.
Large albedo increase + already high albedo (snow) = MUCH more reflected SWdn Raised CO 2 levels and sensitivity = warming Clouds are not important factor RESULT: Cooling (~2.1K, some places exceed 6K)
Global Case
Adding the three zones together is equivalent to the Global Case As stated earlier, net result globally is COOLING by about ~0.3K
Simulated spatial
temperature difference relative to
Standard case centered on year 2100 for global deforestation.
In Summary…
Although removal of forests causes global warming through Carbon-Cycle effects, this warming is overwhelmed by the local and global cooling effects of increased albedo and decreased evapotranspiration, most strongly in the boreal regions.
Conclusions/Opinions
Afforestation in tropics = beneficial Afforestation in temperate and boreal zones = counter productive Complex atmosphere-biosphere dynamic Teleconnection and Feedback Problem Results vary by location Subgrid-Scale Problem Problems with INCCA Model Comparable studies with other models needed Goal should still be preservation of ecosystems