Research shows that Arctic warming has tripled compared to global patterns

Global warming is a pervasive problem, with widespread initiatives to reduce emissions and mitigate emissions against the International Panel on Climate Change’s worst-case scenario projections of 3.2°C of warming by 2100 (relative to from pre-industrial levels). Current measurements indicate a warming of 1.1°C across the globe, but the polar regions are experiencing greater surface warming compared to the rest of the planet.

Quantifying this amplification of warming in the Arctic (>65°N) compared to global averages, and the mechanisms behind this, is the subject of new research published in Natural Geosciences.

Dr. Wenyu Zhou, from the Pacific Northwest National Laboratory, US, and colleagues examined previous reports of Arctic amplification factors of two to four since 1979, and determined that a factor of three is more likely, based on Earth’s natural variability modulating temperature change.

“Natural variability is like noise,” explains Dr. Zhou out. “Even in the absence of external influences (such as changes in greenhouse gases), the state of the climate system can fluctuate due to the coupled dynamics of the ocean, atmosphere and land. Such variability can occur on different time scales (interannual, decadal, multiple). -decadal) depending on the corresponding ‘mode’.

“The observed Arctic strengthening therefore consists of two parts: the part that is forced by external forces and the part that is due to natural variability (which leads to the temporal anomaly in the rate of Arctic strengthening).

“The alarming fourfold strengthening of the Arctic in recent decades challenges our previous beliefs and is rarely reproduced by climate models,” says Dr. Zhou.

“It remains elusive whether this discrepancy reflects a temporal anomaly due to natural variability or a forced Arctic warming that is systematically underestimated by models.”

To investigate this, the research team compared observational data with model simulations, finding that the difference in amplification factor between the two could be explained by natural variability, specifically certain ocean and climate patterns associated with the region. This includes the Interdecadal Pacific Oscillation and the Arctic Internal Mode.

The Interdecadal Pacific Oscillation is a 20- to 30-year pattern of climatic and oceanographic changes in both hemispheres of the Pacific Ocean, where positive phases see warming in the east and cooling in the west, alternating during negative phases.

The negative phase is the most important because it is associated with a higher frequency of La Niña events (trade winds push warm water toward Asia, resulting in the upwelling of cool, nutrient-rich water along the U.S. coastline, which often increases the severity of hurricane season here enlarged), and it has been found that it has had a reducing effect on Arctic warming since 2000.

Meanwhile, the Arctic’s internal mode has been found to have experienced increased warming since 2005. This refers to positive phases resulting in warming over the Kara Sea, with anticyclonic climate patterns bringing moisture to the area, absorbing longwave radiation and heating the surface. , leading to the melting of sea ice.

A sharp decline in sea ice results in ice-albedo feedbacks that lead to further warming. This process occurs because melting sea ice reduces the amount of ‘white’ reflective surface for incoming solar radiation, but instead increases the surface area of ​​the relatively ‘dark’ ocean to absorb radiation, warming the environment and increasing the sea ice continues to melt. continues a runaway feedback loop.

Over the entire study periods of 1970–2004 and 1980–2014, overall, based on observational data, the Arctic enhancement was found to be 2.09 and 3.98, respectively, changing to 2.28 and 3.33 with the removal of the Interdecadal Pacific Oscillation, and then to 2.85 and 2.94 after additional research. removing the effect of the internal Arctic mode.

Consequently, a consistent amplification factor of three is identified, corresponding to that used in Coupled Model Intercomparison Projects (CMIP6), supporting its reliability for predicting future climate change.

“Here we provide clear evidence to show that the previously reported four-fold Arctic amplification is an anomaly caused by dominant modes of natural variability and that the degree of forced amplification is consistently around three throughout the historical period.”

This research is important because it highlights the sensitivity of climate change modeling and the conclusions drawn to predict future patterns of global warming. By taking natural variability into account and identifying an amplification factor of three instead of four, future mitigation strategies may not need to be as severe in the coming decades.

Dr. Zhou and colleagues suggest that in the coming decades, the internal mode in the Arctic is likely to shift to a negative phase and the Interdecadal Pacific Oscillation to a positive phase, which would lead to a reduction in the Arctic amplification factor, perhaps even as low as two.

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