David Whitehouse: The Global Warming Hiatus Is Real

  • Date: 23/06/17
  • David Whitehouse, Financial Post

The global warming ‘hiatus’ is the most talked about and researched topic in climate science

Few things illustrate the poor state of the communication of climate science better than the reaction to Environmental Protection Agency Administrator Scott Pruitt’s comments about global temperatures in the past 20 years. It was made in written comments to the Senate following his confirmation hearing. He wrote, “over the past two decades satellite data indicates there has been a leveling off of warming.” Has the temperature increase of the Earth’s surface and lower atmosphere “stalled” in the past 20 years or so? Does this change our view of climate change?

Condemnation of these comments was swift. A study was quickly put together for the journal Nature Scientific Reports to disprove Pruitt’s comments. It looked at satellite measurements of the temperature of the atmosphere close to the ground back to when such data first became available in 1979. It concluded that Pruitt was wrong and many media outlets reported that conclusion.

But had reporters looked a little deeper into the data, and talked to more scientists, they would have uncovered a far more fascinating story more in keeping with the way science actually works, as climate scientists attempt to decipher real-world climate data. They would have discovered that Pruitt has a point: The world’s surface has not been warming as expected in the past two decades. A great many scientists accept what the data are saying and are seeking to explain it. Others are sure there has been no slowdown, but the problem is they are often not even-handed in their analysis.

The Nature Scientific Reports study reached its erroneous conclusion by considering short-term natural fluctuations to be part of long-term global warming. We have just experienced a few years of strongly elevated global surface and lower atmospheric temperatures due to an El Nino.

El Ninos are natural quasi-periodic events originating in the equatorial Pacific that have worldwide consequences. This is not global warming. However, its elevated temperatures at the end of a temperature-data set skews estimates of how much long-term warming is taking place, making it seem more dramatic than it actually is. Taking this into account, and not assuming that the global temperature increase since 1979 has been constant at the same rate, allows the remarkable stability of the lower tropospheric temperature, and the surface temperature as measured by weather stations and ocean buoys, to become apparent.

Although many prominent climate scientists will not countenance its existence, the so-called “hiatus” is the most talked about and researched topic in climate science. It is a significant mystery for which there have been many explanations proposed with a growing suspicion that perhaps the oceans are involved in some way.

Writing in the journal Nature recently, Gerald Meehl, of the U.S. National Center for Atmospheric Research, said the many adjustments of the surface temperature data sets — adjustments that invariably eliminate the hiatus — have not been as definitive as some suggest. He says the claims of “no hiatus” rest on questionable interpretations of forced climate change due to greenhouse gasses and their relationship with inter-decadal and decadal natural climate variability. The hiatus is clear, he says, and not an artifact of the data.

This means that in the past 20 years or so the anthropogenic warming signal is being obscured by decadal climatic variability and it could be several decades before man’s influence emerged and exceeded nature. As the journal Nature Climate Change said recently, “Longer-term externally forced trends in global mean surface temperatures are embedded in the background noise of internally generated multidecadal variability.” Pruitt’s comments recognize that.

Some are adamant that the “hiatus” does not and never has existed, and will never change their minds. But the evidence is irrefutable. As a large number of influential climate scientists have just said in the journal Nature Geoscience, since the turn of the century there has been a substantial slowdown in warming that computer climate models did not predict or can explain. In fact, such models predict a warming twice that observed. This confirms what Pruitt has said. If anyone tells you that the science is settled tell them that this is just the start of climate science and not its end.

Some scientists and campaigners may find it inconvenient and uncomfortable but the EPA’s Pruitt has a point backed-up by science.

David Whitehouse is a writer and broadcaster, and science editor of the Global Warming Policy Foundation.

Financial Post, 23 June 2017



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