What carbon sinks are saturating? A recent and persistent increase in winds (photo, British Antarctic Survey) “over the Southern Ocean, caused by greenhouse gases and ozone depletion, has led to a release of stored CO2 into the atmosphere and is preventing further absorption of the greenhouse gas”(original Science article here).
Let me quote one key, sobering paragraph from the new study:
Growth in Atmospheric CO2. Global average atmospheric CO2 rose from 280 ppm at the start of the industrial revolution (circa 1750) to 381 ppm in 2006. The present concentration is the highest during the last 650,000 years and probably during the last 20 million years. The growth rate of global average atmospheric CO2 for 2000–2006 was 1.93 ppm. This rate is the highest since the beginning of continuous monitoring in 1959 and is a significant increase over growth rates in earlier decades: the average growth rates for the 1980s and the 1990s were 1.58 and 1.49 ppm respectively.
What is particularly novel about this Proceedings of the National Academy of Sciences paper is that the authors provide the first quantitative explanation I have seen for this accelerated growth rate:
The growth rate of atmospheric CO2 depends on three classes of factors: global economic activity (generated from the use of fossil fuels and land-use change), the carbon intensity of the economy, and the functioning of unmanaged carbon sources and sinks on land and in oceans. Since 2000, a growing global economy, an increase in the carbon emissions required to produce each unit of economic activity, and a decreasing efficiency of carbon sinks on land and in oceans have combined to produce the most rapid 7-year increase in atmospheric CO2 since the beginning of continuous atmospheric monitoring in 1959. This is also the most rapid increase since the beginning of the industrial revolution.
We estimate that 35% of the increase in atmospheric CO2 growth rate between 1970–1999 and 2000–2006 was caused by the decrease in the efficiency of the land and ocean sinks in removing anthropogenic CO2 (18%) and by the increase in carbon intensity of the global economy (17%). The remaining 65% was due to the increase in the global economy.
The longer we delay, the deeper we will have to cut emissions to stabilize concentrations, especially because the carbon sinks are saturating.
The study’s lead author, Dr Pep Canadell, executive director of the Global Carbon Project, explained “Fifty years ago, for every tonne of CO2 emitted, 600kg were removed by natural sinks. In 2006 only 550kg were removed per tonne and that amount is falling.”
The authors, from the Global Carbon Project, have put online a great PPT presentation here. Kudos to the GCP for their work.