Economist Ross McKitrick

Economist Ross McKitrick
The dire climate prediction made by former NASA scientist James Hansen "significantly overstates the warming" observed in the real world since the 1980s, according to an analysis.

Economist Ross McKitrick and climate scientist John Christy found observed warming trends match the low-end of what Hansen told Congress during a hearing on global warming organized by then-Congressman Al Gore.

"Climate modelers will object that this explanation doesn't fit the theories about climate change," the two wrote. "But those were the theories Hansen used, and they don't fit the data. The bottom line is, climate science as encoded in the models is far from settled."

Cato Institute climate scientists Patrick Michaels and Ryan Maue wrote that "surface temperatures are behaving as if we had capped 18 years ago the carbon-dioxide emissions responsible for the enhanced greenhouse effect."

"But we didn't. And it isn't just Mr. Hansen who got it wrong," Michaels and Maue wrote in The Wall Street Journal in June.

The WSJ op-ed set off a fierce debate over the accuracy of Hansen's predictions. Several media reports interviewing climate scientists claimed Hansen's predictions - issued in 1988 - were pretty much correct.

Hansen's dire global warming predictions turned 30 this year, sparking fawning media coverage of their accuracy. The so-called "godfather" of global warming even told The Associated Press "I don't want to be right in that sense."

Some scientists moved the goalposts and argued even though Hansen's temperature predictions were off, he got the radiative forcing from greenhouse gas emissions correct.

However, McKitrick and Christy's analysis takes into account such objections, pointing out that Hansen's prediction of carbon dioxide emissions were actually close to what was observed - there just wasn't much warming.

It turns out Hansen's middle-of-the-road projection of global warming, known as Scenario B, only takes carbon dioxide emissions into account, but still showed too much warming, McKitrick and Christy wrote.

"What really matters is the trend over the forecast interval, and this is where the problems become visible," McKitrick and Christy wrote, noting Hansen's top two scenarios "significantly overstates the warming."

Hansen's predictions also did not include the incredibly strong El Nino warming events, including the most recent one that peaked in 2016. Likewise, Hansen's predictions also included volcanic eruptions that depressed global temperatures.

"Thus, to make an apples-to-apples comparison, we should remove the 2015 volcanic cooling from Scenarios B and C, and add the 2015/16 El Nino warming to all three Scenarios," McKitrick and Christy wrote. "If we do that, there would be a large mismatch as of 2017 in both A and B."