Arctic temperatures are rising four times faster than global warming

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A new analysis of observed temperatures shows that the Arctic is warming more than four times faster than the rate of global warming. The trend has risen sharply twice in the past 50 years, a conclusion missed by all but four of the 39 climate models.

“Thirty years is considered the minimum to represent climate change,” said Petr Chylek, a physicist and climate researcher at Los Alamos National Laboratory and lead author of the study in Geophysical Research Letters. “We narrowed the time interval to 21 years. At this smaller timescale, and unlike previous investigations which found that the Arctic Amplification Index increases steadily, we observed two distinct stages, a in 1986 and a second in 1999.”

Since the episodic decadal trend identified by Chylek and his collaborators affects global climate and sea levels, accurately projecting future climate change within shorter timeframes is critical to planning any mitigation of its impacts and developing coping strategies. The Arctic influences the world’s climate and weather, and the melting of the Greenland Ice Sheet is causing sea level rise that threatens many coastal communities.

The amplification index in the study is the ratio of a 21-year arctic temperature trend to a global 21-year temperature trend.

The study calculated that the Arctic Amplification Index was greater than 4 in the first decades of the 21st century, four times faster than the global average and considerably faster than previous published research had determined. using time intervals of 30 to 40 years. These earlier studies set the index between 2 and 3.

From 39 climate change models from the widely used CMIP6 collection of the Coupled Model Intercomparison Project, the international research team found four that reproduced the first stage reasonably well around 1986, but none that reproduced the second stage. in 1999. CMIP is an international collaboration of climate models using a common set of parameters. CMIP6 was used to create the recent Intergovernmental Panel on Climate Change assessment report.

“We attributed the first stage to increasing concentrations of carbon dioxide and other pollutants in the atmosphere, because several models do this correctly,” Chylek said, “but we think the second stage is due to climate variability because none of the models can reproduce the second stage.”

Short-term climate variability is generally not detected by climate models with their time scales of more than 30 years.

The study does not identify a cause for these relatively sudden increases, but the authors speculate that contributing causes are likely sea ice and water vapor feedbacks combined with changes in how atmospheric heat and oceanic moves into the Arctic. Future increases in the Arctic Amplification Index will likely be smaller as the temperature difference between the Arctic and the tropics decreases.

Useful for projecting change in the Arctic

Chylek said the research team will then study future Arctic climate projections using the four models that come closest to the observed warming trend, with the spikes.

“Because all four models correctly reproduce at least the first step, we assume they are somewhat better for future climate projections,” Chylek said. “People usually average all models and assume that the ensemble is more reliable than any single model. We show that averaging doesn’t work in this case.”

The research team downloaded publicly available temperature data for the Arctic from the Internet and used simulations from climate models in the CMIP6 collection.

“People are not only interested in long-term climate change, but they are also interested in the next 10 years, 20 years, 30 years. For the decadal forecast, our observation that the amplification index has changed in stages in the past is quite significant”. Chylek said.

The research team included members from Los Alamos, University of East Anglia, PAR Associates, University of Washington, Pacific Marine Environmental Laboratory and Dalhousie University.

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More information:
Petr Chylek et al, Annual Mean Arctic Amplification 1970–2020: Observed and Simulated by CMIP6 Climate Models, Geophysical Research Letters (2022). DOI: 10.1029/2022GL099371

Provided by Los Alamos National Laboratory

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Teresa H. Sadler