Matt Ridley uses a Wall Street Journal column to ask an inconvenient question for climate alarmists: Whatever happened to global warming?

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.