Global Cycles

1
Global Cycles

• Part IV Integration
• Chapin, Matson and Mooney
• Principles of Terrestrial Ecosystem Ecology

2
(No Transcript)
3
Half of global biomass and a third of global NPP
is in tropical forests
4
(No Transcript)
5
Atmospheric CO2 concentration is rising
6
(No Transcript)
7
Rising atmospheric CO2 causes climate to warm
8
Most major greenhouse gases are increasing in
atmospheric concentrations
9
(No Transcript)
10
Earth is experiencing directional changes in many
drivers of climatic and ecological processes
Steffen et al. 2004
11
We usually treat climate change and land-cover
change as separate problems
But they are linked
12
Nature of linkages

• Climate effects on ecosystems
• Temperature
• Precipitation
• Wind, etc.

13
Nature of linkages

• Climate effects on ecosystems
• Ecosystem effects on climate
• Trace gas emissions (CO2, CH4, N2O)
• Atmospheric chemistry (CO, VOC, O3)
• Aerosol emissions (atmos. forcing and deposition)
• Water and energy exchange
• River runoff (altered ocean circulation)
• Effects via nutrient loading on biological pump
  (CO2 drawdown)
• Effects on salinity, density, ocean circulation

14
Nature of linkages

• Climate effects on ecosystems
• Ecosystem effects on climate
• Society-mediated effects
• Trace gas emissions (climate)
• Land-cover change (ecosystems)
• Ecosystem modification (ecosystems)

15
Spatial scale of linkage depends on turnover time

• Turnover time Spatial scale
• CO2 3 years Global
• CH4 8.4 years Global
• N2O 120 years Global
• Water 10 days Sub-continental
• Aerosols Days to weeks Regional to Continental
• NOx lt 1 day Regional
• Energy Instantaneous Local-Regional
• Global atmospheric mixing 1 year

16
Integration of carbon with energy and water
budgets
17
Photosynthesis Long-term growth
Short-term growth Long-term growth
Canadell
18
CO2 effects on C cycle
Net effects Carbon sequestration
Globally dispersed cooling
19
A broader set of interactions and
feedbacks weakens the cooling effect with time
20
CO2 effects on carbon, energy, and water balance
21
CO2 fertilization feedbacks

• Trace-gas feedbacks predominate (cooling)
• CO2 often stimulates C sequestration (cooling)
• NPP stimulated by CO2 in 2/3 of studies
• Global modeling of climate trends requires CO2
  fertilization effect
• Effect saturates
• Down-regulation of photosynthesis (stomata)
• Reduced plant N status (plant)
• Reduced N mineralization (ecosystem)
• Stimulation of NEP declines over time (few
  studies)
• Most pronounced in young mesic forests
• Energy-budget feedbacks can be substantial
  (warming)
• Less moisture return to atmosphere (warming
  immediate)
• But more leaf area--greater moisture return
  (cooling decades)
• More growth, lower albedo (warming decades)

22
NPP
Changes in carbon balance Small carbon
sink McGuire et al. 2000 Sitch et al. 2007
RH
NEP
23
Warming effects in the Arctic A positive
feedback to warming
Recent change 3.5 W/m2 Shrub expans. 8.9 W/m2
2X CO2 4.4 W/m2
Recent change (per decade) Future change with
shrub conversion
24
Fire alters energy exchange Negative feedback to
climate warming Importance to society depends on
total area burned
Baldochi
25
Changes in surface albedo at the Delta
Chronosequence
Grey line Recent burn Black line Control
Liu et al., 2005
26
Warming effects on carbon, energy, and water
balance
27
Sum of forcing agents yields net warming over the
first year but cooling over 80 years
Randerson et al. 2006
28
Climate warming feedbacks

• Trace-gas feedbacks
• CO2 exchange
• Modest C sink in the Arctic
• Modest C source in boreal forest
• Permafrost thaw potential large future source
• CH4 substantial source
• Energy-budget feedbacks predominate
• Earlier snow melt in the Arctic and Boreal
• positive feedback to warming
• Vegetation change
• Increased shrubs in arctic (positive feedback to
  warming)
• Switch to deciduous in boreal (negative feedback
  to warming)

29
Response to drought
30
Drought effects on carbon, energy, and water
balance
31
Drought feedbacks

• Trace-gas feedbacks small
• Very small NEP
• Energy-budget feedbacks predominate
• Reinforce climate drying or wetting
• Ecosystem feedbacks create non-linear response
• Creates memory that sustains climate regime
• Effects are regional
• Important role for restoration ecology

32
Boreal deforestation might cause net cooling

Converse Boreal afforestation might cause net
warming (Efforts to address C sequestration
alone are counter-productive)
Bala et al. 2007
33
Tropical deforestation causes net warming
Bala et al. 2007
Converse Tropical afforestation causes net
cooling
34
Deforestation effects on carbon, energy, and
water balance
35
Tropical deforestation feedbacks (net warming)

• Trace-gas feedbacks (net warming)
• Carbon loss
• globally dispersed
• Energy-budget feedbacks (net warming)
• Increased ecosystem albedo (cooling)
• But cancelled out by reduced cloudiness
• Reduced transpiration (warming)
• Reduced precipitation
• Half of rainfall comes from recycled water
• Reduces forest growth
• Could trigger switch to savanna/dry conditions
• Climate feedbacks stabilize the vegetation change
• Socioeconomic implications

36
Afforestation effects opposite to those of
deforestation

• Tropical afforestation net climate cooling
• Increased carbon storage (cooling)
• Increased transpiration (cooling)
• Boreal afforestation net climate warming??
• Increased carbon storage (cooling)
• Large decrease in albedo (warming)
• Temperate afforestation small climate warming?

Bala et al. 2007
37
Most major greenhouse gases are increasing in
atmospheric concentrations
38
(No Transcript)
39
Human activities have doubled the global input of
nitrogen to ecosystems
40
(No Transcript)
41
Most major greenhouse gases are increasing in
atmospheric concentrations
42
(No Transcript)
43
(No Transcript)
44
(No Transcript)
45
(No Transcript)
46
(No Transcript)
47
Distribution of water Volume (km3) Percent
of total Oceans 1,350,000,000 97.40 Polar ice
caps and glaciers 27,500,000
1.98 Exchangeable groundwater 8,200,000
0.59 Freshwater lakes 100,000
0.007 Saline lakes 105,000
0.008 Soils 70,000 0.005 Atmospheric
vapor 13,000 0.001 Wetlands 11,500
0.0008 Rivers and streams 1,700
0.0001 Annual inputs Percent of
ocean Riverine to ocean 37,000
0.003 Groundwater to ocean 1,600 0.0001
48
(No Transcript)
49
(No Transcript)
50
(No Transcript)