Global Temperatures May Take Decades to Respond to Emissions Reductions: Study

This June 19 photo shows the land surface temperature in the Siberia region of Russia. (ECMWF Copernicus Climate Change Service via AP)

(CN) — A warming planet will not shake off centuries of human-caused pollution overnight, according to a new study that cautions reductions in human-caused emissions now will take decades to show detectable changes in global surface temperatures. 

While the peak of the ongoing pandemic helped to mitigate global carbon emissions, policymakers will need to be patient with the follow-through, according to researchers from the Center for International Climate and Environmental Research, also known as CICERO.

“This paper is about managing our expectations,” the study led by Bjørn Samset from CICERO in Oslo, Norway, begins.

There is near universal agreement among the scientific community that human activity is responsible for a warming planet. But the results of current attempts to mitigate climate change or a timeframe for when such results will be expected remain unknown.  

“For climate mitigation efforts to maintain public support, it is therefore likely crucial to be able to document the benefits,” the study’s authors wrote in the paper, which was published Tuesday in the journal Nature Communications.

“The question facing us is therefore how to determine that progress has been made towards the ambitions of the Paris Climate Agreement, and that this is a consequence of changes in anthropogenic influence on the climate,” the researchers wrote. 

Samset said the hope was to break the problem of measuring climate change and reductions into smaller parts.

“We confirmed that strong cuts in CO2 emissions is still our best bet for slowing own climate change, although emissions of methane and black carbon are also important,” Samset said in an email.

Through various projection scenarios with sudden reductions in carbon dioxide, methane and black carbon, the study shows detectable changes could take place decades after those reductions are put into effect.

“Consider a year in the future, say 2050,” the study states. “At that time, we will have had 30 measurements of annual mean temperature since 2021.”

A pair of simulations, one featuring a scenario that curbs global emissions and another that keeps things at the same pace, could follow similar paths for decades and not see any discernible fork for some time.

“We were surprised at just how long we risk seeing rising temperatures even under drastic emission cuts, if natural variability drives the climate in that direction,” said Samset. “It was somewhat surprising to see that even in the unrealistic case of totally removing CO2 emissions today, it would likely take a decade or more for the effects to be visible in terms of global temperature. For optimistic but still realistic mitigation scenarios, it would take even longer, simply because there is so much variability from year to year.”

Still, the researchers say that while the results may not be immediately measurable it is still important to try and achieve the goals set in the Paris Climate Agreement.

“Rigorous detection and attribution of the impacts of even very strong mitigation efforts on global mean surface temperature will, for a long time, be challenging,” the study’s authors wrote. “It is therefore imperative that the scientific community explores and clearly communicates the expectations we have in terms of quantifiable, observable impacts.”

The most significant contributions to the planet would come from reductions in carbon dioxide, methane and black carbon, according to the researchers. The coming decades will see change, it is just a matter of being patient. Whether or not that means a cooler planet depends on how human’s answer today.

According to Samset, cuts to emissions are effective from the first day but the delayed response means that researchers should focus on quantifying the emissions themselves along with concentrations of greenhouse gases and not simply relying on global surface temperature.

“It took us a while to prove conclusively that global warming was happening,” said Samset. “Now, when this has been known for decades, it’s going to take us a while to prove conclusively that we’re managing to do something about it. This should of course not stop us from cutting. It should, however, remind us to curb our expectations.”

Tuesday’s study coincides with the monthly report from the European Union’s climate monitoring network, which revealed last month is in a dead heat for the warmest June on record globally — driven largely by blistering heat waves in Siberia and throughout the Arctic Circle.

Hourly temperature records for the month were set in Verkhoyansk in northeastern Russia, which saw a peak of nearly 99 degrees on June 21 according to the Copernicus Climate Change Service. Another weather station in the town registered 100.4 degrees at one point in the day.

The service also warned fire danger across Siberia and the Arctic Circle is high and “intense activity” in the coming weeks is likely. Additionally, “zombie” blazes that have been smoldering throughout the winter since 2019 — a record year for wildfires across the region — may have reignited, the service said.

Globally, June was nearly 1 degree warmer than the 1981-2010 average for the month, more or less tied with June 2019 as the warmest on record.


Agence France-Presse contributed to this report.

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