7:15 AM | *Another summer with nearly normal temperatures in the Arctic region continues a long-term trend during their melting season...Arctic sea ice showing resiliency*
Paul Dorian
As long as temperatures in the Arctic region remain close-to-normal during the summer season (gray area), there will likely be a limit as to the amount of melting of sea ice. The plot shown here displays the actual temperature pattern through mid-July (orange) as compared to the mean temperatures in the Arctic region (blue) and indeed, temperatures have been nearly normal during the summertime which continues a long-term trend. Data courtesy Danish Meteorological Institute
Overview
The summer is more than half over up in the Arctic region and overall temperatures this season are repeating a pattern that began many years ago in that they are running at nearly normal levels which happens to be quite close to the freezing mark. The cold season in the Arctic has featured above-normal temperatures in the Arctic region in a pattern that has also been very consistent in recent years. It is the temperatures in the summer months of June, July, and August, however, which are the most important when it comes to Arctic sea ice extent as this is the melting season up in that part of the world. As long as temperatures remain nearly normal during the summer (melting) season, the chance for any additional significant drop off in sea ice will be limited. Indeed, given this consistent summertime temperature trend in recent years, Arctic sea ice has shown resiliency both in terms extent and in volume. One possible explanation of this persistent temperature pattern across the Arctic region with nearly normal summertime conditions and warmer-than-normal in the other nine months of the year (i.e., the cold season) is increased levels of water vapor in the atmosphere.
The temperature pattern in the Arctic region during the last many years has featured nearly normal levels during the summer (melting) season and above-normal conditions during the cold months. Data courtesy Danish Meteorological Institute
Arctic temperatures and the impact on sea ice
Temperatures have followed a persistent trend in the Arctic region during the past several years, in fact, going all the way back to the beginning of the 21st Century. Specifically, temperatures have been running at nearly normal levels during the all-important summer (melting) season of June, July, and August and then usually at well above-normal levels during the remaining nine months of the year.
Anomaly of the +80N mean temperature index is shown here back to 1960, compared with climate (annual mean minus the corresponding climate value). “All year” anomaly is illustrated with the black line and has climbed since the middle 1990s. The “summertime” anomaly of June, July, and August is illustrated with red and has held at nearly normal levels. An important shift in the Atlantic Multidecadal Oscillation (AMO) took place during the middle 1990’s when it flipped from a “negative-to-positive” phase. Reference climate is ECMWF-ERA40 1958-2002. Plot courtesy Danish Meteorological Institute
Nearly normal temperatures in the summer months of June, July and August are typically at levels near or just above the freezing mark and as long as they remain there during the melting (summer) seasons, chances for any significant drop-off in Arctic sea ice will be limited. Well above-normal temperatures in the other nine months of the year have minimal impact on the melting of Arctic sea ice as they are typically well below the freezing mark. Indeed, with this dependable temperature trend in recent years, Arctic sea ice has been rather resilient both in terms of extent and volume.
The daily moving average of Arctic sea ice (shown in green) has been rather level since 2007 and so has the yearly maximum (red) and yearly minimum (bottom) values. Map courtesy NOAA, realclimatescience.com
Arctic sea ice extent has been running at below-normal levels since the middle 1990’s at which time there was an important shift in the Atlantic Multidecadal Oscillation (AMO) to one featuring warmer-than-normal sea surface temperatures in the North Atlantic Ocean. The Arctic sea ice extent headed steadily downward after that shift and reached its lowest point in 2012 at levels not seen before during the satellite era which goes back to the late 1970’s. Since then, Arctic sea ice extent has held rather steady with a general sideways trend during the past decade or so.
Arctic sea ice volume as estimated by the University of Washington’s PIOMAS numerical model shows resilience during the last ten years or so with a “sideways” trend. This model output data is updated on a monthly basis and is shown here through June 2024. Details on the PIOMAS model are available here.
In addition to sea ice extent, an important climate indicator to monitor is sea ice volume as it depends on both ice thickness and extent. Arctic sea ice volume is difficult to monitor on a continuous basis as observations from satellites, submarines and field measurements are all limited in space and time. As a result, one of the best ways to estimate sea ice volume is through the usage of numerical models which utilizes 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-derived Arctic sea ice volume shows a steady downward trend from the middle 1990s to the low point that was reached in 2012. Since then, Arctic sea ice volume has been showing resiliency with a general sideways trend during the past several years.
Relative humidity (left) and surface temperatures (right) have averaged higher-than-normal during the wintertime in the Arctic region (indicated with arrows) for the last ten years (2013-2023). An increase in water vapor (and relative humidity) in the cold, dry cold season of the Arctic can have much more of an impact on air temperatures as compared to during the warmer summer (melting) season. Maps courtesy NOAA/NCAR
Possible role of water vapor
One possible explanation for the behavior of temperatures in the Arctic region during the past couple of decades has to do with increased amounts of water vapor in the atmosphere. Overall, water vapor content has been higher-than-normal in the Arctic region during the past couple of decades largely as the result of warmer-than-normal sea surface temperatures in both the North Atlantic (positive AMO) and the Pacific Ocean (multiple El Nino events).
Given the warmer-than-normal water temperatures, there has been increased evaporation and this, in turn, generates more overall water vapor in the atmosphere. An increase in water vapor will have a much bigger impact on temperatures in very cold and dry atmospheres and less of an impact in a warmer and more humid environment. In other words, an increase in overall water vapor could very well result in warmer-than-normal temperatures during the cold seasons in the Arctic region when it is typically very cold and dry, and likely have little, if any, impact during the warmer, more humid summer (melting) season.
Meteorologist Paul Dorian
Arcfield
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