Groups and Networks

As regards the greenhouse gases carbon dioxide (CO₂) and methane (in particular), the link of these to climate is now firm. The ice-cores not only preserve a detailed and reproducible record of global temperature (deduced from isotope ratios); they also contain a record of atmospheric composition, now going back three-quarters of a million years, as bubbles of gas trapped in the ice layers (see Sources listed above). As temperatures rose and fell, so did the levels of these gases in the atmosphere.

It is also undoubted that levels of CO₂ are now some 30% higher than at any time over the past 750 000 years, (with levels of methane having more than doubled). CO₂ levels are now increasing, seemingly inexorably, by nearly 1% a year, and the trend is accelerating. It is also beyond doubt that these increases are due to human activity, particularly the burning of fossil fuels, rather than being due to, say, volcanic activity. Levels of human-sourced emission dwarf anything produced by even the largest recent eruptions (e.g. Krakatoa) and the ice-core record shows that, while records of past massive eruptions are preserved as layers rich in volcanic dust and sulphur dioxide, there are no CO₂ ‘spikes’ of eruptive origin.

Sources
Recent assessments of the global CO₂ balance, including figures on anthropogenic emissions include:

• Quay, P. 2002. Ups and downs of CO₂ uptake. Science, vol. 298, p. 2344.
• Sarmiento, J.L. & Gruber, N. 2002. Sinks for anthropogenic carbon. Physics Today (August 2002), pp. 30-36.
• Page, J.L. et al. 2002. Amount of carbon released from peat and forest fires in Indonesia during 1997. Nature, vol. 420, pp. 61-65 (and also discussed on pp. 29-30 of the same issue)