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Q. The current “message” about global warming is that it is entirely caused by man-made greenhouse gas emissions, predominantly CO2. But there is an alternative view that increasing CO2 levels are a consequence of solar flares, which are causing the sea temperature to rise and releasing dissolved CO2. Also, the amount of CO2 which is attributable to mankind is 10% of the global increase and we in Britain generate just 2% of global CO2 emissions. Please can you comment on these alternative views, quoting the references that you rely on in giving your answers? (Paul Thorne, by e-mail)
A. The "alternative views" are opinions held by some people, but they are not backed up by scientific evidence. You appear to have been told part of the story, but not all of it!
Changes in the sun have exerted only a minor warming influence (Lean, 2000; see also http://ipcc-wg1.ucar.edu/wg1/Report/AR4WG1_Pub_Ch02.pdf, section 2.71 for a state-of-the-art discussion) and cannot account for the measured rise in sea temperatures (Stott et al, 2000; see also http://ipcc-wg1.ucar.edu/wg1/Report/AR4WG1_Pub_Ch09.pdf). There is a two-way exchange of CO2 between the ocean waters and the atmosphere: about 90 billion tonnes of carbon per year are released from the oceans to the atmosphere, but (and this is the bit you seem not to have been told!) this is more than offset by an uptake of about 92 billion tonnes of carbon per year from the atmosphere by the oceans (Le Querre et al, 2005; Manning and Keeling 2006; Sarmiento and Gruber, 2006; see also http://ipcc-wg1.ucar.edu/wg1/Report/AR4WG1_Pub_Ch07.pdf). The fact that CO2 is overall being absorbed by ocean waters rather than released is further demonstrated by the fact that ocean waters are becoming slightly more acidic (CO2 is a weak acid which reacts with water to produce carbonic acid which, after further chemical reactions, ultimately results in proportionally more H+ ions remaining in solution in the water, which increases acidity. The pH of surface ocean waters has decreased by 0.1 pH units since the industrial revolution (lower pH means greater acidity). (http://ipcc-wg1.ucar.edu/wg1/Report/AR4WG1_Pub_Ch07.pdf).
In actual fact, there are more than enough CO2 emissions attributable to mankind to account for the global increase in atmospheric CO2. We are emitting just over 7 billion tonnes of carbon per year by fossil fuel emissions and cement production (Marland et al, 2006), and approximately a further 2 billion tonnes through deforestation (Houghton, 2003). If all the fossil fuel CO2 remained in the atmosphere, the atmospheric CO2 concentration would be rising by over 3 parts per million per year (Marland et al, 2006). However, the measured rise in CO2 is only about 1.7 parts per million per year (Keeling and Whorf, 2005). This is because the ocean waters and natural land ecosystems are actually removing some of the CO2 from the atmosphere, buffering us from the full effect of our CO2 emissions (again see http://ipcc-wg1.ucar.edu/wg1/Report/AR4WG1_Pub_Ch07.pdf). Without this ecosystem service, the past CO2 rise (and hence past global warming) would have been larger.
So the alternative views you quote are not supported by the evidence, they are based on incomplete information.
References:
Houghton, R.A., 2003a: Revised estimates of the annual net flux of carbon to the atmosphere from changes in land use and land management 1850-2000. Tellus, 55B(2), 378–390.
Keeling, C.D., and T.P. Whorf, 2005: Atmospheric CO2 records from sites in the SIO air sampling network. In: Trends: A Compendium of Data on Global Change. Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, U.S. Department of Energy, Oak Ridge, TN, http://cdiac.esd.ornl.gov/trends/co2/sio-keel-flask/sio-keel-flask.html.
Le Quéré, C., et al., 2005: Ecosystem dynamics based on plankton functional types for global ocean biogeochemistry models. Global Change Biol., 11, doi:10.1111/j.1365-2486.2005.001004.x.
Lean, J., 2000: Evolution of the sun’s spectral irradiance since the Maunder Minimum. Geophys. Res. Lett., 27, 2425–2428.
Manning, A.C., and R.F. Keeling, 2006: Global oceanic and land biotic carbon sinks from the Scripps atmospheric oxygen flask sampling network. Tellus, 58B(2), 95–116.
Marland, G., T.A. Boden, and R.J. Andres, 2006: Global, regional, and national CO2 emissions. In: Trends: A Compendium of Data on Global Change. Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, U.S. Department of Energy, Oak Ridge, TN, http://cdiac.esd.ornl.gov/trends/emis/tre_glob.htm.
Sarmiento, J.L., and N. Gruber, 2006: Ocean Biogeochemical Dynamics. Princeton University Press, Princeton, NJ, 503 pp.
Stott et al (2000) External control of 20th century temperature by natural and anthropogenic forcings. Science, 290, 2133-2317
The web links are to relevant chapters of the IPCC Fourth Assessment Report, which themselves contain a wealth of further references to other peer-reviewed literature.
