9:15 AM | *Arctic temperatures running nearly normal in the summer (melting) season continuing a trend this century…Arctic sea ice showing resiliency in recent years*
Paul Dorian
We are now several days into the month of July and temperatures in the Arctic region are running at nearly normal levels averaging slightly above the freezing mark. As long as temperatures remain nearly normal in the summer months, there will likely be a limit as to the melting of Arctic sea ice. Indeed, with nearly normal summertime temperatures in recent years, Arctic sea ice has been rather resilient in terms of both extent and volume. Data courtesy Danish Meteorological Institute (last updated July 9th, 2023)
Overview
Temperatures are running at nearly normal levels this summer in the Arctic region and this has been a very consistent trend in the 21st Century during the months of June, July and August. Meanwhile, temperatures during the remaining nine months of the year have been regularly measured at well above-normal levels in the Arctic region. It is the summer season, however, that is especially important with respect to Arctic sea ice as this is the melting time of year in the region. Temperatures during the summer season in the Arctic typically average just slightly above the freezing mark whereas during the rest of the year - though usually well above the climatological averages - they usually are way below freezing with minimal impact on ice melt. As long as Arctic temperatures remain nearly normal during the summer (melting) season, the chance for a significant drop off in sea ice will be limited. Indeed, given this consistent temperature trend in recent decades, Arctic sea ice has shown resiliency both in terms extent and in volume. One possible explanation of this reliable temperature pattern across the Arctic this century has to do with increased levels of water vapor in the atmosphere.
These yearly plots going back to 2017 show the daily mean temperature north of the 80th northern parallel as a function of the day of year. The general temperature pattern in this six-year time period (as well as in the current year of 2023) has featured nearly normal temperatures in the summer (melting) season and well above-normal values in the nine months before and after. In fact, this kind of annual temperature pattern has persisted since the beginning of the 21st Century. Temperature data is estimated from the average of 00Z and 12Z analysis for all model grid points. The ERA40 reanalysis data from the ECMWF has been applied to calculate daily mean temperatures for the period of 1958-2002. Data plots courtesy Danish Meteorological Institute (DMI). More information on this data can be found here.
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 often at well above-normal levels during the remaining nine months of the year. (Interestingly, one exception to this non-summertime temperature trend in the Arctic actually took place this year as temperatures during the month of May were well below-normal in the region).
Nearly normal temperatures in the summer months of June, July and August are typically at levels just slightly above the freezing mark and as long as they remain there during this the melting season, 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 - even though they may average at well above-normal levels - they are generally way 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.
This plot shows the annual Atlantic Multidecadal Oscillation (AMO) detrended index values from the 1850’s to the present. There was an important shift in the AMO during the middle 1990’s from negative-to-positive (indicated by arrow on plot) associated with a warming of sea surface temperatures in the Northern Atlantic Ocean. The thin blue line indicates 3-month averages and the thick blue line represents the 11-year rolling average. Data source: NOAA’s Earth System Research Laboratory, last full year shown is 2022, diagram updated January 2023
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 ten years or so.
Graph showing monthly Arctic sea ice extent since the year 2000. The area covered by sea ice is defined as having at least 15% sea ice cover. Thin blue line shows monthly values, and the thick blue line shows the running 13-month average. The red line shows the 1979-2021 average. After a steady decline between year 2000 and the low point reached in 2012, Arctic sea ice extent has been rather stable in the last ten years or so and has actually trended up some in the most recent couple of years. Data provided by the National Snow and Ice Data Center (NSIDC). Last month shown: May 2023. Latest figure update: 9 June 2023.
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.
Arctic sea ice volume as estimated by the University of Washington’s PIOMAS numerical model (Note – this model output data is updated on a monthly basis, details on the PIOMAS model are available here.
Importance 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).
Relative humidity and surface temperatures have averaged higher-than-normal during the wintertime in the Arctic region (indicated with arrow) for the last ten years (2012-2022). An increase in water vapor (and relative humidity) in the cold, dry winter season of the Arctic can have an important impact on surface temperatures. Maps courtesy NOAA/NCAR
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 atmospheric conditions 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 when it is typically very cold and dry, and it would likely have little, if any, impact during the warmer, more humid summer (melting) season.
Meteorologist Paul Dorian
Arcfield
arcfieldweather.com