Modelling the Response of the Biological Pump to Climate Change

Abstract

The concentrations of so-called “greenhouse” gases, carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O) and halocarbons and other halogenated compounds, are increasing in the atmosphere mainly due to human activities. These gases trap outgoing radiation from the Earth’s surface, causing a warming of the lower atmosphere. The fate of carbon produced from fossil fuel emissions has received a great deal of attention both in scientific circles and in the media. The present atmospheric CO2 increase is caused by anthropogenic emissions of this gas, about three quarters of which are due to fossil fuel burning which released 6.3 ± 0.4 Gt C yr-1 between 1990 and 1999 (IPCC 2001). The remainder is due to land use change. The resulting atmospheric CO2 increase is 3.2 ± 0.1 Gt C yr-1. This increase is less than the emissions because the ocean and terrestrial biosphere sequester much of the carbon. The flux from atmosphere to ocean is estimated to be 1.7 ± 0.5 Gt C yr-1 between 1990 and 1999 (IPCC 2001). The large volume of the ocean, in conjunction with the chemistry of the marine carbonate system, means that it potentially has the capacity to continue taking up CO2 of anthropogenic origin for at least several centuries.