The Arctic has warmed ‘nearly four times faster’ than the global average

“Arctic amplification” may be stronger than previously thought, according to new research.

The phenomenon means Arctic temperatures are rising much faster than the global average, with previous estimates finding the region is warming two times as quickly.

However, new research published in Communications Earth and Environment suggests that the Arctic has warmed nearly four times faster than the global average over the past four decades.

The authors find that climate models “struggle” to accurately simulate Arctic amplification, consistently underestimating its value. However, scientists not involved in the research note that there are uncertainties in observations of Arctic warming for the regional definition chosen, and advise caution in this conclusion.

The study is “inspirational”, a scientist not involved in the study tells Carbon Brief, adding that it will raise awareness about the “limitation of current climate models in fully capturing some critical physical processes that drive Arctic Amplification in the real world”.

Arctic amplification
Global temperatures have already increased by around 1.3C due to human activity. However, warming is not consistent across the planet – some regions have warmed significantly faster than others. The Arctic is a hotspot for global warming, and has seen local temperatures rise much faster than the global average in recent decades – a phenomenon known as Arctic amplification.

In this study, the authors use observational data to investigate how temperatures in the Arctic circle have changed since 1950. The plot below shows temperatures in the Arctic circle (dark lines) and global average temperatures (faded lines), compared to the average 1981-2010 temperature. Each colour represents a different dataset of observations.

Temperature anomaly in the Arctic (dark lines) and for the global average (faded lines) compared to the 1981-2010 average
Temperature anomaly in the Arctic (dark lines) and for the global average (faded lines) compared to the 1981-2010 average. Source: Rantanen et al (2022).
The graph shows that temperatures in the Arctic have warmed 3.8 times faster than the global average since the late 1970s.

This value is much higher than the numbers cited by previous studies. The latest report from the Intergovernmental Panel on Climate Change says “it is very likely that the Arctic has warmed at more than twice the global rate over the past 50 years”. Meanwhile, the recent Arctic Monitoring and Assessment Programme report says that the Arctic is warming three times faster.

It can be tricky to estimate the rate of Arctic amplification, because uncertainty in Arctic warming is inherently high in models, Dr Matthew Henry – a postdoctoral research fellow at the University of Exeter, who was not involved in the study – tells Carbon Brief:

“The uncertainty in the magnitude of Arctic warming is inherently larger than that of global warming. Global warming uncertainty is mainly due to cloud feedbacks, whereas Arctic warming uncertainty arises from sea ice, cloud, aerosol, and atmospheric and oceanic heat transport processes.”

Rapidly rising Arctic temperatures are driven by a range of processes, including the “surface albedo feedback”, in which melting sea ice uncovers the darker water beneath. This reflects less of the sun’s rays back into space, allowing further warming and melting. Arctic amplification is strongest in the late autumn and early winter, when the ice-free ocean releases heat into the atmosphere.

The Arctic circle
The lack of consensus on Arctic amplification in existing literature is partly because there is no fixed definition of where the Arctic begins and ends. The Arctic can be defined using the area poleward of a given latitude – 60N, 65N and 70N are often used – but there are also definitions not based on latitude, the study notes.

This is important because warming is not uniform across the Arctic. The maps below show warming per decade (left) and Arctic amplification across the northern polar region (right), using the average of four observational datasets. The Arctic circle – defined at 66N latitude – is shown by the dotted line.

Darker colours in the map on the left indicate faster decadal warming. In the map on the right, values above one indicate that the area is warming faster than the global average. For example, a value of two means the area is warming twice as fast as the global average.

The authors investigate how changing the regional definition and the time window used affects Arctic amplification. Each box in the figure below shows Arctic amplification for a single region and time window. Darker colours indicate a higher Arctic amplification and the star shows the region and time window chosen in this study.

Moving up the chart moves the boundary used to define the Arctic region closer to the pole. Meanwhile, moving from left to right increases the time window over which Arctic amplification is calculated. For example, 10 years on the x axis corresponds to the trend calculated over 2011–21, and 30 years corresponds to 1991-2021.

Dr Judah Cohen – director of seasonal forecasting at Atmospheric and Environmental Research (AER), who was also not involved in the study – tells Carbon Brief that “most amplified warming is over the ocean”. As such, the high Arctic amplification found in this study is in part because the regional definition excludes most of the Arctic lands, he says.

The authors find that using a shorter, more recent time window results in a lower Arctic amplification – indicating that in recent decades, the Arctic has warmed at a similar speed to the rest of the planet. This could mean that warming in the Arctic has slowed down, or warming in the rest of the world has sped up, Rantanen tells Carbon Brief.

This finding “highlights the importance of exploring the sensitivity of Arctic amplification to its definition”, Prof Karen Smith – an assistant professor at the University of Toronto Scarborough, who was not involved in the study – tells Carbon Brief.

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