Carbon Cycle2

8/13/2019 Carbon Cycle2

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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

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