Avoiding climate catastrophe will probably require going to near-zero net emissions of greenhouse gases this century. That is the conclusion of a new paper in Geophysical Research Letters (subs. req’d) co-authored by one of my favorite climate scientists, Ken Caldeira, whose papers always merit attention. Here is the abstract:

Current international climate mitigation efforts aim to stabilize levels of greenhouse gases in the atmosphere. However, human-induced climate warming will continue for many centuries, even after atmospheric CO2 levels are stabilized. In this paper, we assess the CO2 emissions requirements for global temperature stabilization within the next several centuries, using an Earth system model of intermediate complexity. We show first that a single pulse of carbon released into the atmosphere increases globally averaged surface temperature by an amount that remains approximately constant for several centuries, even in the absence of additional emissions. We then show that to hold climate constant at a given global temperature requires near-zero future carbon emissions. Our results suggest that future anthropogenic emissions would need to be eliminated in order to stabilize global-mean temperatures. As a consequence, any future anthropogenic emissions will commit the climate system to warming that is essentially irreversible on centennial timescales.

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According to the new U.S. study, North America released 1,856 million metric tons of carbon into the air in 2003 — 85 percent from the United States, 9 percent from Canada and 6 percent from Mexico.

At the same time, growing vegetation and other sources took in about 500 million metric tons of carbon.

This is the first net carbon report for the region, said Tony King, lead researcher on the report and chief scientist at Oak Ridge National Laboratory.

A group of U.S. researchers have found that wildfires — fuelled by climate change — may be turning boreal forests into sources of carbon dioxide.

The boreal forests — found in northern Canada, Alaska, Siberia, China, Scandinavia and elsewhere — make up the second largest type of forest in the world behind the tropical rainforest.

Scientists have historically believed that the boreal forests act as a carbon sink, as trees absorb carbon emissions and reduce them in the atmosphere.

But new research from the University of Wisconsin-Madison, published in the Nov. 1 issue of the journal Nature, has found that the forests may be emitting more carbon than they are absorbing.

“Moreover, even this seemingly unreachable 60% cut by 2050 is still nowhere near enough. The
latest science indicates that a cut of no less than 90% is necessary by the much earlier date
of 2030 if we are to keep carbon concentrations in the atmosphere below 430 parts per million.
The significance of this threshold is that above this level we may not be able to prevent some of
the potentially catastrophic feedback processes from kicking in: such as the dieback of the
Amazon rainforest, the release of billions of tons of methane hydrates from the ocean floor, or the
collapse of the Greenland and Antarctica ice sheets. After that, nature takes over and the
biosphere becomes the primary producer of carbon. The global warming process takes on a
momentum of its own, beyond our control” (Meacher 2007).

Many of the works surveyed in this report express this urgent view, and argue that atmospheric
greenhouse gases should be reduced from the current level of 430ppm to 350-400pmm CO2e
(Meinshausen 2005, Retallack 2005, Harvey 2006a), requiring further emission cuts to near zero.
Britain’s Environment minister David Miliband says “essentially, by 2050 we need all activities
outside agriculture to be near zero carbon emitting if we are to stop carbon dioxide levels in the
atmosphere growing” (Miliband 2006).

“This is the climate equity challenge, and it must now be set in the context of largely non-negotiable global emissions reductions on the order of 80 percent by 2050. As an organisation that advocates on behalf of the world’s poorest communities, Christian Aid supports the least risky and therefore most stringent pathway to decarbonisation. Therefore, step one in defining climate equity is to set a global carbon budget, within which all countries, industrialised and developing, have a legal obligation to remain.”

Pendleton leads the climate change policy work at Christian Aid.

Andrew Weaver and colleagues at the University of Victoria in Canada say this means going well beyond the reduction of industrial emissions discussed in international negotiations.

Weaver’s team used a computer model to determine how much emissions must be limited in order to avoid exceeding a 2°C increase. The model is an established tool for analysing future climate change and was used in studies cited in the IPCC’s reports on climate change.

They modelled the reduction of industrial emissions below 2006 levels by between 20% and 100% by 2050. Only when emissions were entirely eliminated did the temperature increase remain below 2°C.

A 100% reduction of emissions saw temperature change stabilise at 1.5°C above the pre-industrial figure. With a 90% reduction by 2050, Weaver’s model predicted that temperature change will eventually exceed 2°C compared to pre-industrial temperatures but then plateau…
“People are easily misled into thinking that 50% by 2050 is all we have to do when in fact have to continue reducing emissions afterwards, all the way down to zero,” Lenton says.”

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