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Climate change and the carbon cycle
David Schimel
National Center for Atmospheric Research
Boulder Colorado
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Indicators of the Human Influence
on the Atmosphere during the Industrial Era
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Climate changeThe climate is
changing, the climate
has always beenchanging and we are
now accelerating the
process intouncharted territory
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SPM 1b
Variations of the Earths surface temperature
for the past 1,000 years
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SPM 1a
Variations of the Earths surface temperature
for the past 140 years
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These line plots are misleading by
suggesting climate changes
uniformly everywhere-change tends
to occur non-uniformly in time and
space
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Percent of the continental USA with a much above normal proportion of total
annual precipitation from
1-day extreme events (more than 2 inches or 50.8mm)
Karl et al. 1996
BW 7
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The carbon cycle
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Global carbon exchange is highly variable
Keeling record, Dargaville plot
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Fossil fuels are not naturally a part of the fast cycle: every ton
emitted changes the carbon cycle for thousands of years
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Global patterns of land and ocean uptake
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Key point: Most uptake is occurring in the disturbed and
managed ecosystems of the Northern Mid-latitudes where
5-20% of plant growth is being stored
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Carbon emissions and uptakes since 1800
(Gt C)
180
110
115
265
140
Land use
change
Fossilemissions
Atmosphere
Oceans
Terrestrial
The
biosphere
buys time
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Measuring carbon uptake
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What is eddy correlation?
A measurement technique for surface atmosphere exchangeThat makes use of turbulence and concentration measurements
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Global carbon responds to NEE: a small difference
between two large fluxes (NEE =
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Global distribution of Fluxnet sites
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Carbon uptake in the US
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(VEMAP)
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Ancillary data are
scant in the
mountains
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Conclusions
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Most of todays carbon uptake is due to
historical land use changes: this will change
in the future
Carbon exchange is sensitive to climate, and
especially to growing season length changes
Much of the USs uptake is in montane
environments and, in the West, is linked to
fire suppression and recovery of forests from
historical harvest
Carbon management in the US West is
linked to watershed management
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Land management activities can play a critical role
in limiting the build-up of carbon dioxide in the
atmosphere, especially in the near-term
To stabilize the atmospheric concentration of
carbon dioxide (Article 2 of the Convention) will
require significant emissions reductions globally,
which can only be achieved by either reducing
energy emissions or by capture and storage ofenergy emissions
K M
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Key Messages Human activities (fossil fuel use and land-use) perturb the carbon cycle -
- increasing the atmospheric concentration of carbon dioxide
The current terrestrial carbon sink is caused by land managementpractices, higher carbon dioxide, nitrogen deposition and possibly recent
changes in climate
This uptake by the terrestrial biosphere will not continue indefinitely.
The question is when will this slow down, stop or even become a source?
Land management results in the sequestration of carbon in three mainpools -- above and below ground biomass and soils
Monitoring systems can be put in place to monitor all three pools of
carbon
Land management buys time to transform energy systems to lower GHGemitting systems, but will allow more fossil carbon to transferred to the
more labile biological pools, hence avoiding a tonne of carbon emissions
is better than creating a tonne of sinks