Now come climate scientists' implausible explanations for why the 'hiatus' has passed the 15-year mark.
By MATT RIDLEY
Sept. 4, 2014 7:20 p.m. ET THE WALL STREET JOURNAL
On Sept. 23 the United Nations will host a party for world leaders in New York to pledge urgent action against climate change. Yet leaders from China, India and Germany have already announced that they won't attend the summit and others are likely to follow, leaving President Obama looking a bit lonely. Could it be that they no longer regard it as an urgent threat that some time later in this century the air may get a bit warmer?
In effect, this is all that's left of the global-warming emergency the U.N. declared in its first report on the subject in 1990. The U.N. no longer claims that there will be dangerous or rapid climate change in the next two decades. Last September, between the second and final draft of its fifth assessment report, the U.N.'s Intergovernmental Panel on Climate Change quietly downgraded the warming it expected in the 30 years following 1995, to about 0.5 degrees Celsius from 0.7 (or, in Fahrenheit, to about 0.9 degrees, from 1.3).
Even that is likely to be too high. The climate-research establishment has finally admitted openly what skeptic scientists have been saying for nearly a decade: Global warming has stopped since shortly before this century began.
First the climate-research establishment denied that a pause existed, noting that if there was a pause, it would invalidate their theories. Now they say there is a pause (or "hiatus"), but that it doesn't after all invalidate their theories.
Alas, their explanations have made their predicament worse by implying that man-made climate change is so slow and tentative that it can be easily overwhelmed by natural variation in temperature—a possibility that they had previously all but ruled out.
When the climate scientist and geologist Bob Carter of James Cook University in Australia wrote an article in 2006 saying that there had been no global warming since 1998 according to the most widely used measure of average global air temperatures, there was an outcry. A year later, when David Whitehouse of the Global Warming Policy Foundation in London made the same point, the environmentalist and journalist Mark Lynas said in the New Statesman that Mr. Whitehouse was "wrong, completely wrong," and was "deliberately, or otherwise, misleading the public."
We know now that it was Mr. Lynas who was wrong. Two years before Mr. Whitehouse's article, climate scientists were already admitting in emails among themselves that there had been no warming since the late 1990s. "The scientific community would come down on me in no uncertain terms if I said the world had cooled from 1998," wrote Phil Jones of the University of East Anglia in Britain in 2005. He went on: "Okay it has but it is only seven years of data and it isn't statistically significant."
If the pause lasted 15 years, they conceded, then it would be so significant that it would invalidate the climate-change models upon which policy was being built. A report from the National Oceanic and Atmospheric Administration (NOAA) written in 2008 made this clear: "The simulations rule out (at the 95% level) zero trends for intervals of 15 yr or more."
Well, the pause has now lasted for 16, 19 or 26 years—depending on whether you choose the surface temperature record or one of two satellite records of the lower atmosphere. That's according to a new statisticalcalculation by Ross McKitrick, a professor of economics at the University of Guelph in Canada.
It has been roughly two decades since there was a trend in temperature significantly different from zero. The burst of warming that preceded the millennium lasted about 20 years and was preceded by 30 years of slight cooling after 1940.
This has taken me by surprise. I was among those who thought the pause was a blip. As a "lukewarmer," I've long thought that man-made carbon-dioxide emissions will raise global temperatures, but that this effect will not be amplified much by feedbacks from extra water vapor and clouds, so the world will probably be only a bit more than one degree Celsius warmer in 2100 than today. By contrast, the assumption built into the average climate model is that water-vapor feedback will treble the effect of carbon dioxide.
But now I worry that I am exaggerating, rather than underplaying, the likely warming.
Most science journalists, who are strongly biased in favor of reporting alarming predictions, rather than neutral facts, chose to ignore the pause until very recently, when there were explanations available for it. Nearly 40 different excuses for the pause have been advanced, including Chinese economic growth that supposedly pushed cooling sulfate particles into the air, the removal of ozone-eating chemicals, an excess of volcanic emissions, and a slowdown in magnetic activity in the sun.
The favorite explanation earlier this year was that strong trade winds in the Pacific Ocean had been taking warmth from the air and sequestering it in the ocean. This was based on a few sketchy observations, suggesting a very tiny change in water temperature—a few hundredths of a degree—at depths of up to 200 meters.
Last month two scientists wrote in Science that they had instead found the explanation in natural fluctuations in currents in the Atlantic Ocean. For the last 30 years of the 20th century, Xianyao Chen and Ka-Kit Tung suggested, these currents had been boosting the warming by bringing heat to the surface, then for the past 15 years the currents had been counteracting it by taking heat down deep.
The warming in the last three decades of the 20th century, to quote the news release that accompanied their paper, "was roughly half due to global warming and half to the natural Atlantic Ocean cycle." In other words, even the modest warming in the 1980s and 1990s—which never achieved the 0.3 degrees Celsius per decade necessary to satisfy the feedback-enhanced models that predict about three degrees of warming by the end of the century—had been exaggerated by natural causes. The man-made warming of the past 20 years has been so feeble that a shifting current in one ocean was enough to wipe it out altogether.
Putting the icing on the cake of good news, Xianyao Chen and Ka-Kit Tung think the Atlantic Ocean may continue to prevent any warming for the next two decades. So in their quest to explain the pause, scientists have made the future sound even less alarming than before. Let's hope that the United Nations admits as much on day one of its coming jamboree and asks the delegates to pack up, go home and concentrate on more pressing global problems like war, terror, disease, poverty, habitat loss and the 1.3 billion people with no electricity.
Mr. Ridley is the author of "The Rational Optimist" (HarperCollins, 2010) and a member of the British House of Lords.