Transcript Global Carbon Cycle Feedbacks: From pattern to process Dave Schimel NEON inc Fate of Anthropogenic CO2 Emissions (2000-2007) 1.5 Pg C y-1 4.2 Pg y-1 Atmosphere 46% 2.6 Pg.

Global Carbon Cycle
Feedbacks:
From pattern to process
Dave Schimel
NEON inc
Fate of Anthropogenic CO2 Emissions (2000-2007)
1.5 Pg C y-1
4.2 Pg y-1
Atmosphere
46%
2.6 Pg y-1
+
7.5 Pg C y-1
Land
29%
2.3 Pg y-1
Oceans
26%
Canadell et al. 2007, PNAS (updated); Slide from global Carbon Project
The Basic Narrative of Climate Change and the Carbon Cycle
We are changing the Carbon Cycle
Which causes a change in the distribution of
the energy reaching the Earth
Which warms the planet
Energy Balance
Eventually feeding back on the
carbon cycle
Temperature
Which amplifies the climate change,
mainly because of increased water vapor
Water vapor
Which changes the water cycle
Carbon cycle feedbacks
• Terrestrial uptake and release depend on
temperature and precipitation
• Terrestrial uptake depends on atmospheric CO2
concentration
• The above feedbacks depend on nutrient cycles
• Terrestrial carbon storage depends on
ecosystem type, which depends on climate
• And then there are the oceans (for another talk)
– And this all leads to model uncertainty…..
The C4MIP uncertainty figure
Status of global models ?
•
Current models match local and some global observations but often predict
variables and scales that are hard to validate (same problem as in night 1 talks)
•
Current models give drastically different predictions under climate change
despite similar skill levels for the present day
What can we constrain from observations?
Pattern: the interhemispheric gradient
implies a Northern Hemisphere sink
TFT 1990
What does a Northern Hemisphere land sink
imply?
• CO2 fertilization implies a global sink
• The Northern hemisphere is perturbed by historical
land use, air pollution, nonstationary disturbance
regimes (fire)
• Therefore, this spatial pattern suggests weak CO2 and
strong land use+climate effects
• For the purposes of this talk, I will make that
assumption, although recent observational data
suggests it may be false…
Patterns in time:
The impact of carbon–climate feedback on carbon storage
Increased in the north, reduced in the south.
Fung I Y et al. PNAS 2005;102:11201-11206
©2005 by National Academy of Sciences
Regional differences in the change in hydrologic regime and ecosystem productivity with
global warming: positive effects of warming on pant growth dominate in the North, drought in
the South.
Fung I Y et al. PNAS 2005;102:11201-11206
©2005 by National Academy of Sciences
Observational support for the Fung and Doney hypothesis
Middle sites are in the middle
Extratropic mean normalized anomalies in the net spring uptake [dotted black line, expressed
by inverted early summer (June) detrended CO2 concentration] and spring (MAM)
temperature (dotted red line, weighted by NPP) (a) and in the net growing-season uptake
(dotted black line, expressed by inverted seasonal minimum detrended CO2 concentration
taken from the GLOBALVIEW “reference marine boundary layer matrix”) and growing season
(MAMJJA) temperature (dotted red line, weighted by NPP) (b).
Angert A et al. PNAS 2005;102:10823-10827
©2005 by National Academy of Sciences
Model-data fusion
• Detailed analyses at a specific site
Niwot Ridge, Colorado
Self-consistent parameter sets
CS,0 (g m-2)
Self-consistent parameter sets
Fit to the diurnal cycle
(~12 hour time steps)
Fit to daily data: 24 hour
time steps
Observed variability of fluxes
Analyzed variability of processes
Analysis of controls
Warm springs accelerate
growth but also
evaporation, consistent
with information from
spatial flux patterns and
atmospheric CO2 trends
Patterns in time: clues to mechanisms
Emissions from Indonesian wildfire estimated by
inversion of global CO2 data
One more factor:: nutrient loading
Terrestrial
stoichiometry:
equilibration of
plant growth with
water/energy and
nutrients: at
equilbrium,
nutrients and
climate co-vary, in
the transient, not.
Conclusions
Changes to water balance driven by
temperature and moisture dominate the
terrestrial carbon feedback.
Some of these effects are due to effects on
photosynthesis and respiration.
Others are due to changes in disturbance and
vegetation structure.
Requilibration of limiting nutrients will influence,
or dominate, the transient.
Conclusions: the road forward
In the spirit of communicating about climate change, what does
this mean?
1. The terrestrial carbon-climate feedback is net positive,
though internal (nutrient) feedbacks make it less positive
than in simple models
2. Part of this is because of ecosystem destruction and
structural change, which is partly under direct human control
3. A net positive carbon climate feedback is not just an esoteric
feedback on global mean temperature, but implies damages
to agriculture, forestry and associated ecosystem services
that may be far more serious for human society than the
(small to moderate) additional gain in the coupled climate
system.
We are changing the Carbon Cycle…
Upscaling from experiments:
DRI Reno Face study, Nevada