Earth May Take Decades to Cool After We Cut Emissions

Earth May Take Decades to Cool After We Cut Emissions
Students watch a presentation at an event sponsored by NASA to celebrate Earth Day on April 22, 2016, in Washington, DC. (Photo: Brendan Smialowski / AFP, Getty Images)

Imagine an alternate reality where world leaders finally listened to the science and implemented measures to reduce greenhouse gases right now. Well, a new paper shows that at least a decade would pass before the world begins to cool down as a result. Depending on the level of emissions reduction, we may have to wait until 2046 to see global temperatures drop.

Published in Nature Communications on Tuesday, the new paper shows how the planet could respond to global efforts to address the climate crisis. While severe emission cuts are “necessary and urgent,” author Bjørn Hallvard Samset, a senior researcher at the Centre for International Climate Research in Norway, told Earther in an email, the impacts won’t be immediate.

To calculate how long it’ll take to see global warming noticeably reverse, the team of scientists used climate models to assess how long the world would take to cool down over several climate scenarios. What’s novel about their research, however, is that they didn’t stop there.

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The team ran model experiments to see when the climate would significantly react to dropping different types of emissions to zero in 2020 as well as what would happen with a 5% per year reduction. They also looked at following the trajectory of RCP2.6, a common climate model scenario that’s consider the best case for humanity. In addition, the study explored specific types of emissions — including carbon dioxide, black carbon, and methane — to suss out whether a shortcut of sorts was hiding among them that might quickly reduce the rate of warming and “give ourselves some much needed good news,” Samset said. This way, the team could see how strongly one source of emissions affects global temperature.

As it turns out, there is no easy shortcut. The best solution forward remains to cut carbon emissions. Focusing solely on reducing carbon dioxide emissions, the world would avoid more than 0.7 degrees Celsius (1.3 degrees Fahrenheit) warming by 2100. Only cutting black carbon, on the other hand, would only result in 0.09 degrees Celsius (0.16 degrees Fahrenheit) of heating avoided, though the limited cooling benefits would accrue much faster.

The timeframes for when we would see a noticeable dip in the global average temperature vary for each source of heating. If carbon dioxide emissions were to magically zero out by 2020, we wouldn’t see the global surface temperature significantly reflect that until 2033, according to the paper. Under RCP2.6, the impact wouldn’t emerge clearly until 2047. In the 5% per year reduction approach — the most realistic scenario according to Samset — 2044 is the year we’ll see global warming begin to notably reverse if we cut carbon dioxide emissions.

“This is useful as it can allow us to suggest combined emission mitigation strategies that can have a rapid effect on the warming,” Samset said. “Beyond this, however, we’re hoping that being upfront about how noisy global temperature really is — and that there’s a chance we’ll see increasing temperatures for up to a decade even if we make very strong cuts — will help avoid confusion in the future. We will be able to show that cuts are having an effect, but maybe not in terms of global temperature, which is what most people today are paying attention to.”

Naomi Goldenson, an assistant researcher at the University of California, Los Angeles’ Centre for Climate Science who did not work on this paper, told Earther in an email that these findings are “no surprise.” This delay in temperature response is “inevitable” as carbon dioxide carries a long lifetime when in our atmosphere.

Climate deniers may try to use this cooling delay to further their agenda — something Samset worries about — but researchers are steps ahead of them. “We will of course see a reduction in warming after cuts, but it may take several election cycles,” he said.

The public should see through those lies and know that, as Samset said, “cuts are effective from day one.”