Arctic warming could increase isoprene emissions

Isoprene is a naturally occurring compound that’s produced mainly by plants. Once emitted, it forms tropospheric ozone and secondary organic aerosols, which can have a significant—though poorly understood—impact on climate.

Although most isoprene is emitted by Earth’s boreal and tropical forests, researchers estimate that the Arctic and subarctic tundra could become a larger source of this compound in the future. According to a new study, tundra vegetation could emit up to 41% more isoprene than current levels if temperatures in these regions rise by an additional 2 °C (Proc. Natl. Acad. Sci. U.S.A. 2022, DOI: 10.1073/pnas.2118014119).

If that happens, this isoprene increase could alter the rate of Arctic warming in unexpected ways. Ozone is a greenhouse gas, and aerosols can either absorb or scatter radiation depending on their composition. Yet models rarely account for isoprene’s impacts when attempting to predict how the Arctic climate will look in the future, says Riikka Rinnan, an ecologist at the University of Copenhagen. In the new study, Rinnan and her colleagues calculate that even models that account for isoprene could vastly underestimate how much its emission rate will increase as temperatures continue to rise.

According to coauthor Roger Seco, an ecologist who was at the University of Copenhagen during the study, this discrepancy is due to a lack of Arctic measurements. Not only is working in these cold, barren environments difficult, but scientists thought until recently that isoprene couldn’t be produced in large enough quantities there. Rinnan initially pushed back on this idea in the early 2000s, after she decided to measure subarctic isoprene on a whim during an unrelated project. “Some colleagues thought we would be below detection limits,” she recalls. Instead, “isoprene was the dominant compound.”

In the current study, Rinnan and Seco—now a researcher at the Institute of Environmental Assessment and Water Research—used a technique called eddy covariance, which combines isoprene measurements with wind data. The method allowed the researchers to directly measure how much of the compound was being emitted from two field sites, in Sweden and Norway. This technique is different from the methodology used in earlier studies, which artificially perturbed vegetation and were prone to significant biases, explains Hélène Angot, a scientist at Swiss Federal Institute of Technology, Lausanne (EPFL), who wasn’t involved in the work.

Despite the different measurement methods, however, Rinnan and Seco’s new findings generally agree with past results, Angot says. That makes her and other researchers confident that models aren’t accurately capturing how much isoprene the Arctic will produce in the future.

“We don’t understand everything yet about Arctic climate change,” Rinnan says, so it’s important to understand these additional factors, which are often overlooked.