Carbon Confusion

  • Date: 22/11/09
Although carbon dioxide released by human action enters the atmosphere it is not possible to relate that quantitatively to energy data because of our lack of understanding of carbon sinks. Some of the carbon that enters the atmosphere is sequestered naturally, but where, by how much is poorly understood, and is the efficiency of sequestration affected by growing CO2 levels? Mitigating climate change could be done through a drastic reduction in global CO2 emissions. If we can reduce the uncertainty about carbon sinks, then we could better verify the effectiveness of mitigation policies.
Two recent papers about carbon sinks came to the essentially the same conclusion, but were described by scientists and the media in very different ways.
Corinne Le Quere et al in Nature Geoscience say that the fraction of CO2 not absorbed by carbon sinks is likely to have risen suggesting a decline in the efficiency of the sink. The Nature Geoscience team, under the umbrella of the Global Carbon Project, found that over the past 50 years the average fraction of global CO2 emissions that remained in the atmosphere each year has likely increased from 40 per cent to 45 per cent.
They deduced this by analysing the global CO2 budget between 1959 -2008 and examining each component. In 2008 8.7 +/- 0.5 PgC was released they said, (1 Pg = 1 billion tons or 1000 x million tons) an increase of 2% over 2007 and an increase of 29% since 2000. The Keeling Curve over the same period shows an increase from in atmospheric CO2 concentration of 369 ppmv to 384 ppmv, an increase of 4%.
However, Le Quere et al’s conclusion is not as firm as the media, or its associated press releases, make out. Looking at their fig 2e – the residual sum of all sources and sinks between 1959 – 2008 shows that the evidence for an increase is very poor.
This did not prevent the University of East Anglia and the University of Bristol saying in press releases that it was “the strongest evidence yet that the rise in global CO2 continues to outstrip the ability of the worlds natural ‘sinks’ to absorb carbon.” The press release continuing, saying it that sinks respond to climate change and variability suggesting that if the natural carbon sinks are becoming less efficient then more man-made CO2 emission will stay in the atmosphere and contribute to global warming.
Wolfgang Knorr, also of the University of Bristol, (Geophysical Research Letters, Vol 36, L21710, Nov 2009) saw no decrease in the fraction of atmospheric CO2 being absorbed since 1850. The trend found in the airborne fraction being 0.7 +/- 1.4 % per decade, ie nothing. He also suggests that estimates of carbon emissions from land use changes probably have been overestimated.
Of the current 10 billion tonnes of carbon emitted annually as CO2 by human activities, only about 40%, (Jones and Cox, 2005) remains in the atmosphere, the difference being removed by oceans and land biota in about equal measure. This figure has been remarkably stable for at least several decades. Why this airborne fraction has remained constant is an important question.
http://www.nature.com/ngeo/journal/vaop/ncurrent/abs/ngeo689.html
http://www.bris.ac.uk/news/2009/6676.html
http://www.uea.ac.uk/mac/comm/media/press/2009/nov/homepagenews/globalcarbonproject
http://www.agu.org/pubs/crossref/2009/2009GL040613.shtml
http://www.bristol.ac.uk/news/2009/6649.html
http://www.bristol.ac.uk/news/2009/6678.htmlCarbon confusion.
Although carbon dioxide released by human action enters the atmosphere it is not possible to relate that quantitatively to energy data because of our lack of understanding of carbon sinks. Some of the carbon that enters the atmosphere is sequestered naturally, but where, by how much is poorly understood, and is the efficiency of sequestration affected by growing CO2 levels? Mitigating climate change could be done through a drastic reduction in global CO2 emissions. If we can reduce the uncertainty about carbon sinks, then we could better verify the effectiveness of mitigation policies.
Two recent papers about carbon sinks came to the essentially the same conclusion, but were described by scientists and the media in very different ways.
Corinne Le Quere et al in Nature Geoscience say that the fraction of CO2 not absorbed by carbon sinks is likely to have risen suggesting a decline in the efficiency of the sink. The Nature Geoscience team, under the umbrella of the Global Carbon Project, found that over the past 50 years the average fraction of global CO2 emissions that remained in the atmosphere each year has likely increased from 40 per cent to 45 per cent.
They deduced this by analysing the global CO2 budget between 1959 -2008 and examining each component. In 2008 8.7 +/- 0.5 PgC was released they said, (1 Pg = 1 billion tons or 1000 x million tons) an increase of 2% over 2007 and an increase of 29% since 2000. The Keeling Curve over the same period shows an increase from in atmospheric CO2 concentration of 369 ppmv to 384 ppmv, an increase of 4%.
However, Le Quere et al’s conclusion is not as firm as the media, or its associated press releases, make out. Looking at their fig 2e – the residual sum of all sources and sinks between 1959 – 2008 shows that the evidence for an increase is very poor.
This did not prevent the University of East Anglia and the University of Bristol saying in press releases that it was “the strongest evidence yet that the rise in global CO2 continues to outstrip the ability of the worlds natural ‘sinks’ to absorb carbon.” The press release continuing, saying it that sinks respond to climate change and variability suggesting that if the natural carbon sinks are becoming less efficient then more man-made CO2 emission will stay in the atmosphere and contribute to global warming.
Wolfgang Knorr, also of the University of Bristol, (Geophysical Research Letters, Vol 36, L21710, Nov 2009) saw no decrease in the fraction of atmospheric CO2 being absorbed since 1850. The trend found in the airborne fraction being 0.7 +/- 1.4 % per decade, ie nothing. He also suggests that estimates of carbon emissions from land use changes probably have been overestimated.
Of the current 10 billion tonnes of carbon emitted annually as CO2 by human activities, only about 40%, (Jones and Cox, 2005) remains in the atmosphere, the difference being removed by oceans and land biota in about equal measure. This figure has been remarkably stable for at least several decades. Why this airborne fraction has remained constant is an important question.
http://www.nature.com/ngeo/journal/vaop/ncurrent/abs/ngeo689.html
http://www.bris.ac.uk/news/2009/6676.html
http://www.uea.ac.uk/mac/comm/media/press/2009/nov/homepagenews/globalcarbonproject
http://www.agu.org/pubs/crossref/2009/2009GL040613.shtml
http://www.bristol.ac.uk/news/2009/6649.html
http://www.bristol.ac.uk/news/2009/6678.htmlCarbon confusion.

Although carbon dioxide released by human action enters the atmosphere it is not possible to relate that quantitatively to energy data because of our lack of understanding of carbon sinks. Some of the carbon that enters the atmosphere is sequestered naturally, but where, by how much is poorly understood, and is the efficiency of sequestration affected by growing CO2 levels? Mitigating climate change could be done through a drastic reduction in global CO2 emissions. If we can reduce the uncertainty about carbon sinks, then we could better verify the effectiveness of mitigation policies.

Two recent papers about carbon sinks came to the essentially the same conclusion, but were described by scientists and the media in very different ways.

Corinne Le Quere et al in Nature Geoscience say that the fraction of CO2 not absorbed by carbon sinks is likely to have risen suggesting a decline in the efficiency of the sink. The Nature Geoscience team, under the umbrella of the Global Carbon Project, found that over the past 50 years the average fraction of global CO2 emissions that remained in the atmosphere each year has likely increased from 40 per cent to 45 per cent.

They deduced this by analysing the global CO2 budget between 1959 -2008 and examining each component. In 2008 8.7 +/- 0.5 PgC was released they said, (1 Pg = 1 billion tons or 1000 x million tons) an increase of 2% over 2007 and an increase of 29% since 2000. The Keeling Curve over the same period shows an increase from in atmospheric CO2 concentration of 369 ppmv to 384 ppmv, an increase of 4%.

However, Le Quere et al’s conclusion is not as firm as the media, or its associated press releases, make out. Looking at their fig 2e – the residual sum of all sources and sinks between 1959 – 2008 shows that the evidence for an increase is very poor.

Quere_fig_2e

This did not prevent the University of East Anglia and the University of Bristol saying in press releases that it was “the strongest evidence yet that the rise in global CO2 continues to outstrip the ability of the worlds natural ‘sinks’ to absorb carbon.” The press release also says that that carbon sinks respond to climate change and variability suggesting that if the natural carbon sinks are becoming less efficient then more man-made CO2 emission will stay in the atmosphere and contribute to global warming.

Wolfgang Knorr, also of the University of Bristol, Geophysical Research Letters (press release) saw no decrease in the fraction of atmospheric CO2 being absorbed since 1850. The trend found in the airborne fraction being 0.7 +/- 1.4 % per decade, ie nothing. He also suggests that estimates of carbon emissions from land use changes probably have been overestimated. Press release discussing both papers.

Of the current 10 billion tonnes of carbon emitted annually as CO2 by human activities, only about 40%, (Jones and Cox, 2005) remains in the atmosphere, the difference being removed by oceans and land biota in about equal measure. This figure has been remarkably stable for at least several decades. Why this airborne fraction has remained constant is an important question.

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