There’s been a much-ballyhooed slowdown in the rise of global land surface temperatures since 1998. The so-called “hiatus,” a leveling off of the long-term surface warming trend, has been used by some to argue—incorrectly—that anthropogenic climate change has stalled. Warming in the ocean more than makes up the difference.
This modern pause is not, of course, the only hiatus on record. Yet the question examined by Maher et al. is whether that will continue to be the case—in the shadow of rampant anthropogenic warming, will we continue to see long stretches without surface warming?
Hiatus periods, defined as any 10-year stretch with a global negative trend in surface temperatures, have cropped up before and will happen again. Large volcanic eruptions, variability stemming from large climate systems such as the Interdecadal Pacific Oscillation, and even the effects of anthropogenic aerosols have all previously contributed to similar pauses in surface warming, such as those that occurred from 1937 to 1950 and from 1956 to 1968.
Based on analyses using 31 climate models, however, Maher et al. found that the era of warming hiatuses may soon be coming to an end. Anthropogenic warming, they found, will soon make it unlikely that the world will ever again see a prolonged downturn in the temperature. The authors’ calculations focused only on short-term to midterm climate drivers and ignored longer-term factors such as orbital forcing.
Running their model ensemble under two scenarios (the Intergovernmental Panel on Climate Change’s representative concentration pathway (RCP) 4.5, which sees anthropogenic emissions taper off by the end of the century, and RCP 8.5, which sees unconstrained greenhouse gas emissions), the authors found that as emissions increase, hiatus periods become increasingly rare. Under RCP 8.5, they found that past the year 2032, hiatus periods are unlikely to occur; in addition, by the end of the century, even a large Krakatoa-style volcanic eruption would be unlikely to cause enough cooling to counteract accumulated warming and trigger a hiatus. (Geophysical Research Letters, doi:10.1002/2014GL060527, 2014)
—Colin Schultz, Freelance Writer
Citation: Schultz, C. (2015), Warming hiatus periods to become increasingly unlikely, Eos, 96, doi:10.1029/2015EO022321.