May 4, 2017

Scientists finally have an explanation for the global warming ‘hiatus’

While scientists are in near-universal agreement that climate change is a thing and that humans played a significant role in causing it to happen, there is one area that has caused some confusion and fueled climate skeptics – the so-called warming “hiatus” that lasted from 1998 to 2012.

Now, however, new research published online this week in the journal Nature has attempted to provide answers by explaining that part of the confusion stemmed from short-term changes, the amount of unaccounted for heat stored in oceans, and incomplete observational data.

Another factor, according to Buzzfeed and the Los Angeles Times, is the fact that three different definitions have been used, scientifically, for the term hiatus: one suggesting that there had been no detectable warming or a period of cooling between 1998 and 2012, one indicating that the rate of warming had slowed down during that span, and one suggesting that there had been warming, but that it was less significant than computer models had predicted.

Thus, whether or not there was a warming hiatus depended largely upon which definition and which dataset that an individual referenced when making the argument, lead researcher Dr. Iselin Medhaug of the Institute for Atmospheric and Climate Science at ETH Zurich and his colleagues explained. In their new report, they set out to reconcile those discrepancies.

Among climate scientists, the so-called hiatus was viewed as a short-term variation which had little to no impact on long-term warming trends, but it nonetheless became a hot-button issue in the media and among politicians, particularly those who deny or are skeptical of climate science and referenced it when presenting their arguments against greenhouse gas regulation.

Authors ‘confident’ that humans are responsible for climate change

In early drafts of Intergovernmental Panel on Climate Change (IPCC)  reports being prepared at the time, the study authors said, “the global warming hiatus was considered to be consistent with natural variability, and hence not in need of a detailed explanation.” That, coupled with the lack of scientific studies on the phenomenon at the time, caused the issue to be largely dismissed.

“The interest of the media and public grew, and groups with particular interests used the case to question the trust in both climate science and the use of climate models,” they wrote. So in their new study, Dr. Medhaug’s team set out to analyze existing research and data and explain exactly what happened to the climate between 1998 and 2012.

What they found, according to the Times, is that predictions of warming did not match the data from the time period because researchers failed to include poorly-understood, short-term climate factors – meaning that the data was incomplete. For example, data from heavily affected regions in the Arctic is limited, they said, and while ocean temperatures are accounted for in global mean temperature readings, they typically were not included in model-based predictions.

Furthermore, as The Guardian noted,  higher-than-average wind speeds were observed during the hiatus period, meaning that some warming was not recorded in surface measurements. The researchers also found that climate models failed to perfectly characterize factors, such as how much solar radiation was actually emitted during a given year, or the degree to which volcanic activity and human-produced aerosols played a role in causing conditions to become cooler.

“A combination of changes in forcing, uptake of heat by the oceans, natural variability, and incomplete observational coverage reconciles models and data,” the authors wrote. “Combined with stronger recent warming trends in newer datasets, we are now more confident than ever that human influence is dominant in long-term warming.”


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