What does 20 year hiatus in rise in global temperatures mean for global warming?
The mismatch between rising greenhouse-gas emissions and not-rising temperatures is among the biggest puzzles in climate science just now. It does not mean global warming is a delusion. Flat though they are, temperatures in the first decade of the 21st century remain almost 1°C above their level in the first decade of the 20th. But the puzzle does need explaining.
The mismatch might mean that—for some unexplained reason—there has been a temporary lag between more carbon dioxide and higher temperatures in 2000-10. Or it might be that the 1990s, when temperatures were rising fast, was the anomalous period. Or, as an increasing body of research is suggesting, it may be that the climate is responding to higher concentrations of carbon dioxide in ways that had not been properly understood before. This possibility, if true, could have profound significance both for climate science and for environmental and social policy. . . .
In fact, over the last 150 years there have been a number of such anomalies. Temperatures rose until the 1930s, then fell until the late 1970s, then rose again after that. How does that possibly fit in with the continually rising CO2 over that period of time? No explanation has been offered for these past inconsistencies.