One other summer time of near-normal temperatures within the Arctic area – Arctic sea ice reveals resilience – Watts Up With That?

By KLIMA-DEPOT

By Marc Morano

https://arcfieldweather.com/blog/2024/7/30/715-am-another-summer-with-nearly-normal-temperatures-in-the-arctic-region-continues-a-long-term-trend- during their melt season

By meteorologist Paul Dorian

As long as temperatures in the Arctic remain close to normal during the summer season (grey area), there will likely be a limit to the melting of sea ice. The graph shown here shows the actually Temperature trend until mid-July (orange) compared to mean Temperatures in the Arctic region (blue) and indeed temperatures were close to normal during the summer, continuing a long-term trend. Data courtesy of the Danish Meteorological Institute

overview

Summer is already more than halfway over in the Arctic and overall temperatures this season are repeating a pattern that began many years ago by running at near-normal levels that happen to be quite close to freezing. The cold season in the Arctic has been characterized by above-average temperatures, a pattern that has been very consistent over the past few years as well. However, temperatures during the summer months of June, July and August are the most important when it comes to Arctic sea ice extent, as this is the melting season in this part of the world. As long as temperatures remain near-normal during the summer (melting) season, the likelihood of further significant sea ice declines is low. Given this consistent summer temperature trend over the past few years, Arctic sea ice has actually proven resilient in both extent and volume. One possible explanation for this persistent temperature pattern throughout the Arctic region, with near-normal summer conditions and warmer-than-average temperatures during the other nine months of the year (i.e., the cold season), is increased water vapor levels in the atmosphere.

Arctic temperatures and the impact on sea ice

Temperatures in the Arctic have followed a consistent trend in recent years, dating back to the beginning of the 21st century. Temperatures were particularly close to normal during the important summer (melt) season in June, July and August, and were usually well above normal during the remaining nine months of the year.

The +80N mean temperature index anomaly is shown here back to 1960, compared with the climate (annual average minus the corresponding climate value). The “all-year anomaly” is shown by the black line and has been increasing since the mid-1990s. The “summertime” anomaly of June, July and August is shown by red and has remained at near-normal levels. An important shift in the Atlantic Multidecadal Oscillation (AMO) occurred in the mid-1990s, when it changed from a “negative to a positive” phase. Reference climate is ECMWF-ERA40 1958-2002. Graph courtesy of the Danish Meteorological Institute

Near-normal temperatures during the summer months of June, July, and August are usually near or just above freezing, and as long as they stay there during the melt season (summer), the likelihood of significant Arctic sea ice decline is low. Well-above-normal temperatures during the other nine months of the year have minimal impact on Arctic sea ice melting, as they are usually well below freezing. In fact, with this reliable temperature trend, Arctic sea ice has been quite resilient in recent years, both in extent and volume.

The daily moving average of Arctic sea ice (shown in green) has remained fairly constant since 2007, as have the annual maximums (red) and minimums (below). Map courtesy of NOAA, realclimatescience.com

Arctic sea ice extent has been below normal since the mid-1990s, when a major shift in the Atlantic Multidecadal Oscillation (AMO) occurred toward a time when sea surface temperatures in the North Atlantic are warmer than normal. Arctic sea ice extent declined steadily after this shift, reaching its lowest level in 2012 with values ​​never before seen during the satellite era, which stretches back to the late 1970s. Since then, Arctic sea ice extent has remained fairly stable, with a general sideways trend during the last decade.

Arctic sea ice volume estimated by the University of Washington's PIOMAS numerical model shows some resilience with a “sideways trend” over the past decade. Model output data is updated monthly and shown here through June 2024. Details of the PIOMAS model can be found here.

In addition to sea ice extent, sea ice volume is an important climate indicator that needs to be monitored because it depends on both ice thickness and ice extent. Arctic sea ice volume is difficult to monitor continuously because observations from satellites, submarines, and field measurements are limited in space and time. Therefore, one of the best ways to estimate sea ice volume is to use numerical models that use all available observations. One such computer model comes from the University of Washington and is called the Pan-Arctic Ice Ocean Modeling and Assimilation System (PIOMAS, Zhang and Rothrock, 2003). This model-based Arctic sea ice volume shows a steady downward trend from the mid-1990s until its low point in 2012. Since then, Arctic sea ice volume has shown resilience, with a general sideways trend over the last few years.

Relative humidity (left) and surface temperatures (right) have been higher than normal on average during winter in the Arctic region over the past decade (2013-2023) (marked with arrows). Increases in water vapor (and relative humidity) during the Arctic's cold, dry cold season can have a much larger impact on air temperatures than during the warmer summer (melt) season. Maps courtesy of NOAA/NCAR

Possible role of water vapor

One possible explanation for the temperature behavior in the Arctic during the last decades has to do with the increased amount of water vapor in the atmosphere. Overall, the water vapor content in the Arctic has been higher than normal during the last decades, mainly due to the above-average sea surface temperatures in both the North Atlantic (positive AMO) and the Pacific (several El Niño events).

Given the above-average sea temperatures, there has been increased evaporation, which in turn leads to a higher total amount of water vapor in the atmosphere. An increase in water vapor has a much larger impact on temperatures in very cold and dry atmospheres, but less so in warmer and wetter environments. In other words, an increase in total water vapor could well lead to above-average temperatures in the Arctic during cold seasons, when it is normally very cold and dry, and would likely have little or no effect during the warmer, wetter summer season (melt season).

Meteorologist Paul Dorian
Arcfield
arcfieldweather.com

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