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Climate models have been right all along, new study says

A study of past climate models found they were accurate compared to what we've observed.

A study of past climate models found they were accurate compared to what we've observed

An oil refinery is pictured at work in Germany. For decades, climate scientists have been sounding the alarm about the effect of greenhouse gases on the atmosphere. (Martin Meissner / The Associated Press)

A recent study of computer climate models detailing back to the 1970s found that they were very accurate when compared to what actually happened in the following decades. This boosts confidence in modern models that predict further change in the future.

In the 1970s, climate scientists began raising a red flag about the increasing amount of carbon dioxide (CO2) being pumped into the atmosphere and its greenhouse effect on warming it. There was also a concern about the rising level of aerosol particles or smog produced by vehicles that could act as a reflector, bouncing sunlight back into space and cooling things down.

To help forecast the long-term climate of the planet, and which way the climate might go, computer models were constructed that took into account the physical characteristics of the atmosphere and how it responds to increased carbon dioxide, methane and other greenhouse gases.

Most models got the physics right

These models were crude by today's standards, but when researchers from the University of California, Berkeley, Massachusetts Institute of Technology and NASA compared the predictions of 17 models published between the early 1970s and the late 2000s to what actually happened, 14 of them were correct. 

The metric used to track the accuracy of the models is the Global Mean Surface Temperature (GMST) that has been tracked by observational surface temperature records for decades. This is the average temperature of the globe over a long period of time, which is the definition of climate. It doesn't predict the day-to-day weather.

The accuracy of the models shows that the climate scientists have been right in their predictions of climate change, and accusations that computer models are inaccurate are false.

One reason some skeptics doubted the models is that they didn't seem to be able to predict how carbon emissions from human activity would change in the future. Those factors are driven by human behaviour rather than atmospheric science. Predicting human behaviour or political decisions is filled with uncertainty. Policies can be put in place to reduce emissions, or things can continue business as usual. It often depends on which government is in power.

Hard to predict future emissions

One famous case of a prediction about climate change that seemed to be wrong was NASA scientist Prof. James Hansen, who reported to the U.S. Senate in 1988. Hansen's climate model predicted that between 1988 and 1997, the average global temperature would rise by 0.45 C. But later, the UN Intergovernmental Panel on Climate Change reported that the climate had warmed by 0.11 C, four times less than Hansen's model predicted. This received huge criticism in the public press.

What really happened is that Hansen's model presented three different scenarios, each with a different result. He reported the worst case of emissions continuing to accelerate, but there was also a best case, where emissions are rapidly reduced. There was also a third case with an outcome in the middle. It turns out that his middle prediction —  and the response of the atmosphere to carbon emissions — was accurate. 

More confidence in today's climate models

This recent study showing that climate models from the past were accurate raises confidence in current models which are far more sophisticated, taking into account much more physics and chemistry of the atmosphere, clouds, oceans and land.

This week, more than 25,000 delegates are gathering in Madrid for the COP25 Climate Conference to discuss ways to implement the goals set out in the Paris Agreement.

Attending is young climate activist Greta Thunberg with a message of urgency on the issue. Much of that urgency comes from computer models that are predicting drastic changes for the climate if something is not done soon.

Now we can believe that those predictions are very likely to come true. 


  • An earlier version of this story stated that the metric used to test the computer climate models is the Global Mean Surface Temperature (GMST) that had been tracked by satellites for decades. In fact, the data came from surface temperature datasets.
    Dec 10, 2019 4:24 PM ET


Bob McDonald is the host of CBC Radio's award-winning weekly science program, Quirks & Quarks. He is also a science commentator for CBC News Network and CBC-TV's The National. He has received 12 honorary degrees and is an Officer of the Order of Canada.