Half a century ago, before the first Apple computer was even sold, climate scientists started making computer-generated forecasts of how Earth would warm as carbon emissions saturated the atmosphere (the atmosphere is now brimming with carbon).
It turns out these decades-old climate models — which used math equations to predict how much greenhouse gases would heat the planet — were pretty darn accurate. Climate scientists gauged how well early models predicted Earth’s relentless warming trend and published their research Wednesday in the journal Geophysical Research Letters.
Most importantly, the results underscore that climate scientists were always right about how greenhouse gases like carbon dioxide trap heat and warm the surface. It was, and is, well-understood science.
“The earliest models were so skillful because the fundamental science behind the greenhouse effect and global warming is well established and fairly straightforward,” said Henri Drake, a Ph.D. candidate researching ocean circulations and climate at MIT. Drake worked on this project for three years.
“The main takeaway is that climate models have, since the 1970s, accurately predicted the future global warming that has occurred since the respective climate model projections were originally published,” Drake added.
After a year of work our paper on evaluating performance of historical climate models is finally out! We found that 14 of 17 the climate projections released between 1970 and 2001 effectively matched observations after they were published. https://t.co/xbmOh4ZPcn 1/19 pic.twitter.com/xjez5FWwd3
— Zeke Hausfather (@hausfath) December 4, 2019
Some decades-old climate models have been labeled “inaccurate” because they either overestimated or underestimated the notoriously unpredictable factor in the warming equation: how much carbon humans might emit from cars, factories, and power plants over the course of decades. This threw off the timing (or specific years) of when models predicted certain amounts of heating might occur. But, critically, the models still did a fine job of predicting how much atmospheric carbon concentrations — the purely scientific component of the models — would actually heat the planet.
“People have for a long time criticized early forecasts for not being perfectly accurate,” said Flavio Lehner, a climate scientist at the National Center for Atmospheric Research who had no role in the new research. But now there’s a scientifically-scrutinized (aka “peer-reviewed” which is the gold standard of research) study showing just how well older models worked, Lehner emphasized.
“This is case and point,” said Lehner. “This is cased closed.”
Of 17 older climate models reviewed (used between 1970 and 2007), 14 closely predicted how much Earth would warm based on the amount of carbon floating around the atmosphere.
Scientists had all they needed to build the first climate models, decades ago. Then and now, climate models take into account how much heat greenhouse gases absorb (known from precise lab measurements), the physics of how Earths’s atmosphere warms (thermodynamics), how much human-created heat gets soaked up by the oceans (most of it), and other factors like the amount of sunlight Earth reflects back into space.
By 1979 the landmark Charney Report, produced by U.S. scientists for the National Academies of Sciences, concluded human carbon emissions were warming the planet. And they accurately projected how much warming would occur in the future. In 1988, NASA scientist James Hansen presented climate projections to Congress, warning the climate would heat up depending on the amount of greenhouse gases civilization ultimately emitted. (Hansen modeled future CO2 concentrations accurately, but overestimated other greenhouse gas influences.)
In 1982, even Exxon’s own scientists would accurately forecast Earth’s temperature increase as carbon emissions soared.
For climate scientists, predicting global temperatures is now considered rather rudimentary stuff. It’s a “pretty low bar,” said Drake. They now have bigger fish to fry.
“The questions we really want answers to are things like: How much will the height of storm surges during major hurricanes landfalls along the U.S. Gulf Coast change due to human-caused climate change?” said Drake. “Will snowstorms in Boston get worse? Which crops will grow best in Uganda in 2050?”
Decades after the first climate models started crunching numbers, atmospheric concentrations of carbon dioxide are higher than they’ve been in at least 800,000 years — though more likely millions of years.
The many consequences of this warming — melting ice sheets, worsening deluges, and crop failures — are evident and growing worse. For climate researchers, looking ahead and forecasting what’s to come is ever-salient.
“What we really want to do is move the field forward,” said Lehner. “This is an opportunity to put to rest fundamental questions about global temperatures and spend time on things we need to understand.”