The Hiatus

Has the climate stopped warming?

Carbon dioxide in atmosphere shows steady rise, so why are temps not higher?

The steadily increasing concentrations of carbon dioxide in the atmosphere since 1998 have not led to the predicted rise in average global temperatures, and this discrepancy has fuelled arguments against climate change as well as confused the public.

Scientists point out that the lack of global temperature rise does fit within their predictions for two possible reasons: surface temperature fluctuations over periods of ten to fifteen years are common, and 1998 was a particularly hot year, making it possibly not the best year for statistical comparison.

Others have put forth a number of alternative explanations.

A US-Australian study published in February suggests that unusually strong Pacific trade winds over the past two decades have been powerful enough to push warm surface water much deeper than previously thought, limiting the amount of heat that goes into the atmosphere, a phenomenon that the models have missed.

Mexican researcher Francisco Estrada points to positive changes such as the ban on chlorofluorocarbons in the atmosphere and the drop in microbial sources of methane as a result of greater use of synthetic fertilizers and more efficient water use to grow rice in Asia.

Climate modellers Benjamin Santer and friends suggest an increase in sulphur aerosols from volcanoes may play a role – or a drop in sea surface temperatures across the eastern equatorial Pacific Ocean due to La Nina. Others argue insufficient data from frequently under sampled parts of the world, in particular the poles and Africa, may be the cause.

Meanwhile, Ocean University of China researcher Xianyao Chen argues in a fresh paper published in Science magazine in August that the heat is being sunk instead in the Southern and Atlantic Oceans, and that the trapped heat in the Pacific is insufficient to account for the pause.

Finally, a commentary in Nature in March brings most of this together to conclude that a gaggle of factors, including volcanic eruptions, the concentration of aerosols in the atmosphere and solar activity, all conspired to dampen warming trends and make the climate modellers look bad.

Ocean researcher Martin Visbeck’s comments in Nature Geoscience that regional fluctuations stress the coping strategies of the developing world.

If you want to read more, researchers John Fyfe, Nathan Gillett and Francis Zwiers of the Canadian Centre for Climate Modelling and Analysis offer a comprehensive commentary, as does Caitlyn Kennedy of the National Oceanic and Atmospheric Administration. For a more popular take on the same topic, Chris Mooney writes up the issue in Mother Jones magazine.