Thirty Years On, How Well Do Global Warming Predictions Stand Up?

Former NASA climate scientist James Hansen famously warned Congress almost 30 years ago to the day that human activities had put the world on the path to disaster, but two scientists now say the global warming “godfather’s” predictions were wrong.

Cato Institute scientists Patrick Michaels and Ryan Maue compared Hansen’s temperature predictions to real-world observations and found his supposedly “highly unlikely” forecast with the least amount of warming was the most accurate.

“Global surface temperature has not increased significantly since 2000, discounting the larger-than-usual El Niño of 2015-16,” Michaels and Maue wrote in a Wall Street Journal op-ed.

“Assessed by Mr. Hansen’s model, surface temperatures are behaving as if we had capped 18 years ago the carbon-dioxide emissions responsible for the enhanced greenhouse effect,” the two scientists wrote. “But we didn’t. And it isn’t just Mr. Hansen who got it wrong.”

“Models devised by the United Nations Intergovernmental Panel on Climate Change have, on average, predicted about twice as much warming as has been observed since global satellite temperature monitoring began 40 years ago,” they wrote. (RELATED: Congress Demands EPA Investigate Potential Collusion With Lobbyists To Thwart Trump’s Agenda)

Climate model accuracy has become a major source of debate as scientists realized predictions diverged greatly from observations over the last 15 years or so. Governments often rely on climate models to justify climate policies or regulations, meaning inaccurate models can yield bad policies.

Hansen laid out three global warming scenarios in 1988 at an iconic congressional hearing: a high-end one where the world warms about 1 degree Celsius by 2018, a middle-range of 0.7 degrees of warming and a low-end estimate with only a few tenths of a degree of warming. The hearing was held on a hot summer day and was organized by none other than former Democratic Rep. Al Gore of Tennessee.

Hansen wished he hadn’t been so accurate in predicting future warming, contradicting Michaels and Maue, he told the Associated Press on Monday. AP claimed Hansen’s predictions had “pretty much come true so far, more or less.”

“I don’t want to be right in that sense,” Hansen said, adding he wished “that the warning be heeded and actions be taken.”

Many other scientists the AP spoke with raved about Hansen’s predictions. Berkeley climate scientist Zeke Hausfather tweeted: “Hansen’s 1988 projections have largely been borne out.”

Hansen’s 1988 projections have largely been borne out, though he predicted modestly higher climate forcings and warming in Scenario B than what occurred. His model’s climate sensitivity (4.2C/doubling of CO2) is also on the high end of current estimates. https://t.co/gtYoK0X2f5 pic.twitter.com/a693ikoy2P

— Zeke Hausfather (@hausfath) June 18, 2018

However, Michaels and Maue said Hansen’s predictions only look correct because of the strong El Nino effect, a naturally occurring warming event, that began in 2015. Global temperatures have actually come down quite a bit since El Nino subsided.

“The problem with Mr. Hansen’s models — and the U.N.’s — is that they don’t consider more-precise measures of how aerosol emissions counter warming caused by greenhouse gases,” Michaels and Maue wrote.

“Several newer climate models account for this trend and routinely project about half the warming predicted by U.N. models, placing their numbers much closer to observed temperatures,” the two wrote. “The most recent of these was published in April by Nic Lewis and Judith Curry in the Journal of Climate, a reliably mainstream journal.”

The two Cato scientists also took on Hansen’s other failed predictions, including those about the Greenland ice melt, temperatures in the U.S. Midwest, hurricanes and tornadoes.

“The list of what didn’t happen is long and tedious,” Michaels and Maue wrote.

“These corrected climate predictions raise a crucial question: Why should people world-wide pay drastic costs to cut emissions when the global temperature is acting as if those cuts have already been made?” they wrote.