We should believe what climate models are telling us: U of T computer scientist

Steve Easterbrook began thinking about his how his research might impact future generations shortly after he arrived at the University of Toronto. 

“I came to U of T in 1999,” says Easterbrook, now director of U of T’s School of the Environment and a professor in the department of computer science in the Faculty of Arts & Science. “My partner and I had just started a family; we became very busy with young kids.”

Having previously worked as lead scientist at NASA’s software verification research lab, where he and his team studied flight software for the Space Shuttle and International Space Station, Easterbrook took a particular interest in the role computer science and software engineering play in understanding and combatting global climate change. He decided to investigate how climate models describe our warming atmosphere – and how well they work.

In his new book, Computing the Climate, Easterbrook explains what climate models are and why we can trust them.

Put simply, climate models are computer programs that simulate the Earth’s atmosphere. Typically, they divide the atmosphere and oceans into three-dimensional blocks – some as small as 30 by 30 kilometres. Mathematical equations simulate the flow of energy, air, moisture through the atmosphere, as well as how the atmosphere interacts with the oceans and land.

To conduct his research, Easterbrook visited climate change labs around the world, including the Meteorological Office in the U.K., the Max Planck Institute for Meteorology in Hamburg, Germany, the National Center for Atmospheric Research (NCAR) in Boulder, Colo., and the Institut Pierre-Simon Laplace (IPSL) in Paris, France.

Easterbrook says he saw first-hand how climate models show with remarkable accuracy how the atmosphere works over long periods. They have provided accurate predictions of the dire consequences of pumping carbon dioxide into the atmosphere for more than a century. He says even models that predated the modern computer, like that of 19th century Swedish chemist Svante Arrhenius, were accurate.

How is it that they’re so trustworthy? According to Easterbrook’s research, it’s because they involve a rigorous global collaborative effort on the part of hundreds of scientists across many disciplines. He says that makes climate models more reliable than most software, which is typically the product of a single, relatively small team’s efforts. While commercial software is tested, it does not undergo the same thorough and rigorous review as climate models.

We should believe these models, he writes in the book, because “climate modelers have built a remarkable set of design and testing practices that look quite unlike anything I've observed in commercial software companies. If you have a large enough community of experts who run the models over and over again, treating each run as though it were a scientific experiment, treating every quirk of the model with the utmost suspicion, it's possible to produce remarkably high-quality software. The result is a quality control process that I believe is unique in the world of computational modeling.”

A high-definition animation of global air circulation by Community Climate System Model (CCSM) and NCAR.

To demonstrate how well climate models work, Easterbrook uses an impressive model developed by NCAR as an example. The model’s output appears as a moving “map” of the world, showing land masses, oceans, clouds, air circulation and precipitation – and looks very similar to animated satellite images. The model correctly simulates details like the daily pulse of rainfall in the Amazon basin and in sub-Saharan Africa, as well as typhoons forming in the western Pacific Ocean that crash into Japan and China.

“None of the patterns you see in this model are directly programmed into it, none are written in the code,” Easterbrook says. “It shows that if you get the physics right, the rotation of the planet, the heating from the sun and cooling off at night, and you run that simulation – these patterns emerge. And they match the planet’s real patterns. That blows my mind.”