Study finds Arctic warming three times greater than global trends

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

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

Dr. Wenyu Zhou of the Pacific Northwest National Laboratory in the United States and colleagues studied previous reports of amplification factors of two to four in the Arctic since 1979 and determined that a factor of three was more likely to be based on Earth’s natural variability that modulates temperature change.

“Natural variability is like noise,” says Dr. Zhou. “Even in the absence of external forcing (such as changing 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 at different time scales (interannual, decadal, multi-annual-decadal) depending on the corresponding “mode”.

“Thus, the observed Arctic amplification consists of two parts: the part forced by external forcing and the part due to natural variability (which leads to the temporal anomaly of the degree of Arctic amplification).

“The alarming four-fold increase in the Arctic in recent decades challenges our previous beliefs and is rarely reproduced by climate models,” says Dr Zhou.

“It is unclear whether this discrepancy reflects a temporary anomaly due to natural variability or a forced state of Arctic warming systematically underestimated by models.”

To explore this, the research team compared observational data to model simulations and found that the difference in amplification factor between the two could be explained by natural variability, particularly by some ocean models and climate associated with the region. This includes the Pacific Interdecadal Oscillation and the Arctic Internal Mode.

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

The negative phase is the most important because it is linked to a higher frequency of La Niña events (the trade winds push warm water towards Asia, causing an upwelling of cool, nutrient-rich water along the coast American, often increasing the severity of the hurricane season here). , and has been shown to have had a reducing effect on Arctic warming since 2000.

At the same time, it is determined that the Arctic internal mode has increased since 2005. This is linked to positive phases leading to warming of the Kara Sea, with anticyclonic climate patterns bringing moisture into the area, which promotes the absorption of long-wave radiation and heating of the surface. , leading to the melting of sea ice.

Strong sea ice decline results in ice-albedo feedbacks that lead to further warming. This process occurs due to melting sea ice, reducing the amount of “white” reflective surface area for incoming solar radiation, instead increasing the relatively “dark” ocean surface area to absorb the radiation, thereby warming the surrounding environment and causing further melting of sea ice which continues an uncontrollable feedback loop.

Overall, over the study periods of 1970 to 2004 and 1980 to 2014, the Arctic amplification was determined to be 2.09 and 3.98, respectively, from observational data, increasing to 2.28 and 3.33 with the removal of the Pacific Interdecadal Oscillation, then to 2.85 and 2.94 after the removal of the Pacific Interdecadal Oscillation. removed the effect of internal Arctic mode.

Therefore, a consistent amplification factor of three is identified, which matches that used in the Coupled Model Intercomparison Projects (CMIP6), confirming its reliability for predicting future climate change.

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

This research is important because it highlights the sensitivity of climate change modeling and the conclusions drawn to predict future global warming trends. Accounting for natural variability and identifying an amplification factor of three instead of four means that future mitigation strategies may not need to be as severe in coming decades.

Indeed, Dr. Zhou and colleagues suggest that the Arctic internal mode will likely shift to a negative phase and the Pacific interdecadal oscillation to a positive phase in the coming decades, leading to a reduction in the amplification of the Arctic, perhaps even as small. like two.

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