Stabilize Climate? Zero Emissions!

” … halfway measures won’t do the job. To stabilize our planet’s
climate, we need to find ways to kick the carbon habit altogether.”

Carnegie Institution
Public release date: 14-Feb-2008

Contact: Ken Caldeira

Stabilizing climate requires near-zero carbon emissions

Now that scientists have reached a consensus that carbon dioxide
emissions from human activities are the major cause of global
warming, the next question is: How can we stop it” Can we just cut
back on carbon, or do we need to go cold turkey” According to a new
study by scientists at the Carnegie Institution, halfway measures
won’t do the job. To stabilize our planet’s climate, we need to find
ways to kick the carbon habit altogether.

In the study, to be published in Geophysical Research Letters,
climate scientists Ken Caldeira and Damon Matthews used an Earth
system model at the Carnegie Institution’s Department of Global
Ecology to simulate the response of the Earth’s climate to different
levels of carbon dioxide emission over the next 500 years. The model,
a sophisticated computer program developed at the University of
Victoria, Canada, takes into account the flow of heat between the
atmosphere and oceans, as well as other factors such as the uptake of
carbon dioxide by land vegetation, in its calculations.

This is the first peer-reviewed study to investigate what level of
carbon dioxide emission would be needed to prevent further warming of
our planet.

“Most scientific and policy discussions about avoiding climate change
have centered on what emissions would be needed to stabilize
greenhouse gases in the atmosphere,” says Caldeira. “But stabilizing
greenhouse gases does not equate to a stable climate. We studied what
emissions would be needed to stabilize climate in the foreseeable

The scientists investigated how much climate changes as a result of
each individual emission of carbon dioxide, and found that each
increment of emission leads to another increment of warming. So, if
we want to avoid additional warming, we need to avoid additional

With emissions set to zero in the simulations, the level of carbon
dioxide in the atmosphere slowly fell as carbon “sinks” such as the
oceans and land vegetation absorbed the gas. Surprisingly, however,
the model predicted that global temperatures would remain high for at
least 500 years after carbon dioxide emissions ceased.

Just as an iron skillet will stay hot and keep cooking after the
stove burner’s turned off, heat held in the oceans will keep the
climate warm even as the heating effect of greenhouse gases
diminishes. Adding more greenhouse gases, even at a rate lower than
today, would worsen the situation and the effects would persist for

“What if we were to discover tomorrow that a climate catastrophe was
imminent if our planet warmed any further” To reduce emissions enough
to avoid this catastrophe, we would have to cut them close to zero –
and right away,” says Caldeira.

Global carbon dioxide emissions and atmospheric carbon dioxide
concentrations are both growing at record rates. Even if we could
freeze emissions at today’s levels, atmospheric carbon dioxide
concentrations would continue to increase. If we could stabilize
atmospheric carbon dioxide concentrations, which would require deep
cuts in emissions, the Earth would continue heating up. Matthews and
Caldeira found that to prevent the Earth from heating further, carbon
dioxide emissions would, effectively, need to be eliminated.

While eliminating carbon dioxide emissions may seem like a radical
idea, Caldeira sees it as a feasible goal. “It is just not that hard
to solve the technological challenges,” he says. “We can develop and
deploy wind turbines, electric cars, and so on, and live well without
damaging the environment. The future can be better than the present,
but we have to take steps to start kicking the CO2 habit now, so we
won’t need to go cold turkey later.”


Source: Matthews, H. D., and K. Caldeira (2008), Stabilizing climate
requires near-zero emissions, Geophysical Research Letters,
doi:10.1029/2007GL032388, in press.

Ken Caldeira is a climate scientist in the Carnegie Institution
Department of Global Ecology at Stanford University. Damon Matthews
is a climate scientist in the Concordia University Department of
Geography, Planning, and Environment in Montreal, Canada.

The Carnegie Institution ( has been a pioneering force in
basic scientific research since 1902. It is a private, nonprofit
organization with six research departments throughout the U.S.
Carnegie scientists are leaders in plant biology, developmental
biology, astronomy, materials science, global ecology, and Earth and
planetary science. The Department of Global Ecology, located in
Stanford, California, was established in 2002 to help build the
scientific foundations for a sustainable future. Its scientists
conduct basic research on a wide range of large-scale environmental
issues, including climate change, ocean acidification, biological
invasions, and changes in biodiversity.


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