Climate change and the carbon cycle

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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 Influenceon the
Atmosphere during the Industrial Era
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Variations of the Earths surface temperature
for the past 1,000 years
SPM 1b
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Variations of the Earths surface temperature
for the past 140 years
SPM 1a
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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)
BW 7
Karl et al. 1996
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The carbon cycle
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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)
The biosphere buys time
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Measuring carbon uptake
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Carbon uptake in the US
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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 of energy emissions

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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 management practices, 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 main pools -- 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 GHG emitting 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