Speeding up detection of climate change response to emission reductions

If humans decrease their greenhouse gas emissions to the atmosphere, how quickly would we detect a slowdown in global warming?

In a recent study published in Nature Communications, Lawrence Livermore National Laboratory (LLNL) climate scientist Mark Zelinka and collaborators developed a novel approach to more quickly see the temperature response to strong emissions reductions.

“Global temperature has very clearly risen over the past 100 years or so, but superimposed on that is a lot of year-to-year variations,” Zelinka said. “These are related to things like El Niño and La Niña events that happen every couple of years that can make one year substantially warmer or cooler than the one before.” 

These natural climate fluctuations create significant “noise” that can mask the underlying “signal” of human-caused temperature changes. This complicates the seemingly simple task of detecting a change in the global warming rate, especially on short timescales of a decade or less.

“We used a tool developed here at LLNL that allows us to filter out these short-term contributions to the global warming rate,” Zelinka explained. “Not only does this allow us to more clearly see the steady upward trend in temperature caused by past greenhouse gas emissions, but we can also use it to better detect a change in the warming rate caused by future emissions reductions,” he added.

While sharp emission reductions will immediately affect global climate evolution, the noise from internal variations mean that — up until now — verification in measurements could take up to 20 years. The new climate variability filter cuts this time in half.

“This will provide crucial confirmation that emission reductions are having an observable effect on the global climate system — information that might otherwise be masked by the noise of natural climate fluctuations,” noted lead author Bjørn Samset, from the CICERO Center for International Climate Research in Norway.

Tools such as these promise a faster way for policy makers to understand the impact of emission reductions on global climate — crucial information for tracking progress towards avoiding dangerous levels of climate change. It also is timely, in light of the just-released Intergovernmental Panel on Climate Change AR6 WG3 report, which highlights the urgency of emissions reductions and provides roadmaps for doing so. 

Other collaborators include researchers from Nanjing University in China, the Max Planck Institute for Meteorology in Germany and Universität Hamburg in Germany. LLNL’s research is funded by the Department of Energy, Office of Science, Regional and Global Model Analysis program area within the Earth and Environmental Systems Modeling Program.