While the present policy debate on climate change focuses on 2020, 2050 and 2100 targets, our present use of fossil fuels will continue to affect the atmosphere and the oceans for many, many thousands of years.
David Archer and Victor Brovkin (2008: 292) point out, “the notion that global warming will last only a few centuries is widespread in the popular and even in the scientific literature on climate change. This misconception may have its roots in an oversimplification of the carbon cycle.”
The IPCC (2007: 515) illustrated the carbon cycle in the 1990s in the following diagram of carbon reservoirs and main annual fluxes (pre-industrial ‘natural’ fluxes in black and anthropogenic fluxes in red):
[Note: Reservoir and main annual fluxes are in Gigatonnes of carbon. These may be converted to CO2 figures by multiplying by 44/12].
In a significant revision of its earlier reports, the IPCC (2007) concluded that natural processes in the carbon cycle will be slow to remove the current levels of CO2 from the atmosphere. Following perturbation of the natural Carbon Cycle about 50% of an increase in atmospheric CO2 will be removed within 30 years, a further 30% will be removed within a few centuries and the remaining 20% may remain in the atmosphere for many thousands of years (IPCC 2007: 514).
Archer and Brovkin (2008) reviewed long-term carbon cycle models from the recently published literature. They noted, “carbon cycle models respond to a release of new CO2 into the atmosphere in a series of several well-defined stages lasting for many millennia.” In the first stage, fossil fuel CO2 released into the atmosphere equilibrates with the ocean, which takes centuries or a millennium due to the slow overturning circulation of the ocean.
Archer and Brovkin (2008: 284) noted that the lifetime of individual CO2 molecules released into the atmosphere may only be a few years because of the copious exchange of carbon with the ocean and the land surface. However, the CO2 concentration in the air remains higher than it would have been, because of the larger inventory of CO2 in the atmosphere/ocean/land carbon cycle.
That is, the equilibrium processes removing fossil fuel CO2 emissions from the atmosphere operate at a system-wide level and individual CO2 molecules do not last for millennia in the atmosphere. Thus today’s fossil fuel CO2 emissions will not be “in” the atmosphere (literally) for a long period but they will continue to “affect” the atmosphere, the climate, and the oceans for many thousands of years.
The equilibrium processes have a major negative side for the oceans. A consequence of the oceans acting as a “sink” for CO2 emitted from burning fossil fuels is ocean acidification, discussed in several recent posts here.
Archer and Brovkin (2008: 288) point out, “after the invasion of fossil fuel CO2 into the ocean, the acidity from the CO2 provokes the dissolution of CaCO3 from the sea floor. … In the models it takes thousands of years for this imbalance to restore the pH of the ocean to a natural value.”
After fossil fuel CO2 in the atmosphere equilibrates with the oceans, atmospheric CO2 will still remain about 20-25% higher than pre-industrial levels. Archer and Brovkin (2008: 287) note that, “eventually, the excess CO2 will be consumed by chemical reactions with CaCO3 and igneous rocks, but this takes thousands of years.”
In an earlier publication, Archer (2005) found that the immense longevity of the tail on the lifetime of CO2 released into the atmosphere means 7% released by burning fossil fuels today will still be affecting the atmosphere in 100,000 years, and the mean lifetime of CO2 in the atmosphere is 30,000-35,000 years. He suggested an appropriate approximation of the lifetime of CO2 released by the burning of fossil fuels for public discussion is “300 years, plus 25% that lasts forever”.
We commonly think of our children and grandchildren to appreciate the consequences of our present actions but as our present emissions of fossil fuel will continue to affect the atmosphere for over 100,000 years, we should appreciate the decisions on climate policies today will affect the next 5,000 generations of humanity and beyond.
Archer D (2005), “Fate of Fossil Fuel in Geologic Time” 110 Journal of Geophysical Research C09S05, doi: 10.1029/2004/2004JC002625
Archer D and Brovkin V (2008), “The millennial atmospheric lifetime of anthropogenic CO2” Climatic Change 90:283-297 DOI 10.1007/s10584-008-9413-1, available at http://geosci.uchicago.edu/~archer/reprints/archer.2008.tail_implications.pdf
IPCC (2007), Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the IPCC (Cambridge University Press, Cambridge). References in text are to Ch 7, pp 514-515 and available at http://www.ipcc.ch/pdf/assessment-report/ar4/wg1/ar4-wg1-chapter7.pdf