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


 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


 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


 6 different model runs (from year 2000-2150): 1.






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


 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.


 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

Any Questions??