Early Climate Change Models Held Up Better Than You Think

Climate models have come a long way. The earliest attempt to estimate what an increase in carbon dioxide could do to surface temperatures on Earth was published in 1896. More projections began to crop up in the ‘60s and ‘70s, at a time when many scientists believed the Earth was actually cooling.

But when atmospheric scientists approximated the effect of rising carbon dioxide and other greenhouse gases, they found a different story: that the world would warm as we continued to burn fossil fuels. In 1967, Syukuro Manabe and Richard. T. Wetherald published their paper “Thermal Equilibrium of the atmosphere with a given distribution of relative humidity,” finding that a doubling of carbon dioxide could lead to a 2.4ºC temperature rise. It’s since been cited over 1,700 times and is considered the first major study to predict global warming.

Those models were far simpler than today’s, missing a lot of the nuances of how the oceans, ice, and atmospheric chemistry interact with increasing emissions. Some climate deniers, wishing to sow doubt, say these early models fail to match reality because their predicted temperatures are higher than what we actually experienced.

Hausfather says that although there had been analyses of how individual models performed, his team’s is potentially the first to systematically evaluate a larger sample. In their study, they included 17 model outputs published between 1970 and 2007. These included ‘70s and ‘80s era models by Manabe and James Hansen, as well as reports by the International Panel on Climate Change.

When comparing temperature across time between projections and reality, most of the models did pretty well. 10 of the projections matched observed temperatures, meaning that the global average surface temperature they predicted in a given year was virtually the same as what we actually recorded. Of the remaining, four predicted more warming than we had and three predicted less.

However, Hausfather says doing just a basic comparison of temperature and time doesn’t do those climate scientists justice. It’s important to realize that climate models not only have to predict how the world works—the physics of greenhouse gases in the atmosphere—but also people’s decisions. Researchers in the ‘70s and ‘80s had to make their best guesses about how much greenhouse gases humans would put into the atmosphere in the future. But Hausfather notes those guesstimates could be as basic as assuming that carbon dioxide would increase by one percent a year. “Today, we have this whole parallel world of energy system models … those modellers then use to run climate models,” says Hausfather. “Back in the ‘70s and ‘80s, none of that existed.”

By – Abhishek Singh

Content -  https://www.popsci.com/story/environment/early-climate-models-correct/