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Will COVID’s Cleaner Skies Muddy Climate Models?

Reduced greenhouse gas emissions for a year or two won’t slow down climate change, but they may throw off scientists’ ability to model short-term phenomena.

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The year 2020 is anomalous for many reasons, but the COVID-19 pandemic that has slowed normal day-to-day activities to nearly a halt stands out.

Earth’s atmosphere has noticed.

In May, a team of international researchers published a paper showing that carbon dioxide emissions had dropped nearly 8% in March and April. And even as the world begins to relax stay-at-home measures and emissions rise once more, the team suggests that the cumulative emissions for this year will remain 4%–7% lower than usual.

In terms of slowing the effects of climate change itself, this year won’t make much of a difference, scientists say. The effects of climate change, like higher sea surface temperatures, more intense rainfall, and retreating glaciers, have more to do with the amount of carbon dioxide that has accumulated in the atmosphere over decades, and one anomalous year won’t affect that.

But will this anomalous year affect the sophisticated models that scientists use to study potential future outcomes of our current levels of greenhouse gas emissions?

How We Model Climate

Scientists feed climate models an enormous amount of data from the tippy top of the stratosphere to the deepest reaches of the ocean. These data include air temperatures, wind speed and direction, cloud properties, concentrations of aerosols and greenhouse gases (like carbon dioxide and methane), ice cover, glacier extent, sea surface temperatures and salinity, current, nutrient cycling, and more.

But what happens to these models if one year is thrown off by an event that affects the world so much that we observe an unprecedented drop in a major variable like carbon emissions?

A team at the University Corporation for Atmospheric Research (UCAR) in Boulder, Colo., is trying to answer that question. Although the drop in emissions has been relatively small, it is still significant, Jean-Francois Lamarque, director of the Climate and Global Dynamics (CGD) Laboratory at UCAR, told Eos. Over the next year or so, “how will it translate into a climate signal that we can observe? That’s a real question [the answer to which] we just don’t know.”

Diverging Timelines

Basically, the team wants to know how different climate projections will be as a result of the pandemic. It’s like seeing a timeline suddenly split, said Gokhan Danabasoglu, a senior scientist in the CGD Laboratory. There exists a set of emissions “as usual,” but now a new timeline has emerged—emissions during a pandemic.

For long-term models, like those modeling the outcomes over the next century of anthropogenic emissions of greenhouse gases and aerosols, the reduction this year probably won’t make a difference, said Qiang Fu, a professor of atmospheric science at the University of Washington in Seattle who is not involved in the UCAR project.

But this anomalous year might affect our ability to model shorter-term and regional climate phenomena, Lamarque said. If the difference in carbon emissions between this year and last year—due to the pandemic—is statistically significant, then that might affect how scientists forecast shorter-term phenomena, like a hurricane season.

But the UCAR team doesn’t have the answer yet. The team has only just begun asking the questions and designing experiments.

One thing is for certain. “Maybe this very unfortunate event is giving us the opportunity to gain an understanding of how the [climate] system responds” to sudden changes in carbon dioxide emissions, Lamarque said.

—JoAnna Wendel (@JoAnnaScience), Science Writer

Citation: Wendel, J. (2020), Will COVID’s cleaner skies muddy climate models?, Eos, 101, https://doi.org/10.1029/2020EO146323. Published on 02 July 2020.
Text © 2020. The authors. CC BY-NC-ND 3.0
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