Ash plume from Eyjafjallajokull Volcano over the North Atlantic on April 17, 2010.
Photo: © NASA Goddard Space Flight Center

Why global warming is taking a break

Mean global warming has hardly increased over the last 16 years. Scientists from the ETH Zurich have identified the reasons for this. They stress that climate warming will soon start up again.

Climate change and global warming are currently taking a break. Whereas global temperatures significantly rose right into the 1990s, global warming has only risen slightly since 1998, despite the fact that greenhouse gas emissions into the atmosphere continued to increase and scien-tific climate models hence projected pronounced global warming. 

In a study published in Nature Geoscience in 2014, scientists from the ETH Zurich (Eidgenö-ssische Technische Hochschule Zürich) conclude that two major reasons were equally responsi-ble for the hiatus.

One major reason is, of course, climate variability. Being a year with a pronounced El-Niño-effect, 1998 was especially warm, say the scientists. The opposite phenomenon, La Niña, how-ever, made recent years colder than they would have been without this phenomenon.

Although climate models basically take such fluctuations into account, it is not possible to pro-ject which years the phenomena will occur.

The second major reason for the global warming hiatus is, according to the study, that in recent years solar radiation was less intensive than forecast. This has to do with the fact that the known fluctuations in the solar radiation intensity are currently atypical. Whereas in the past there was an eleven year sunspot cycle, for unknown reasons the last period of weaker solar radiation lasted 13 years. Moreover, several volcanic eruptions such as the Eyjafjallajökull erup-tion in Iceland in 2010 caused an increase in atmospheric aerosol. This further reduced solar radiation onto the earth’s surface.

But the scientists note that despite the break in global warming there is no reason to question the existing calculations on the climate activity of greenhouse gases or the recent climate mod-els. Global warming will start up again as soon as solar activity and aerosol concentrations in the atmosphere and the climate phenomena such as El Niño return naturally to the levels of early decades.

Study: Huber M, Knutti R: Natural variability, radiative forcing and climate response in the re-cent hiatus reconciled. Nature Geoscience, Online- Published 17 August 2014, doi: 10.1038/ngeo2228

(ETH/ile)