8:00 AM | *The Arctic is experiencing yet another summer ice melting season with normal temperatures*
Paul Dorian
Temperature analysis in the Arctic region from the Japanese Meteorological Agency (JRA-55 Reanalysis); Courtesy Dr. Ryan Maue, weathermodels.com
Overview
In recent days, Arctic sea ice volume has been running at levels above the mean of the base period from 2004-2013 and it is above the levels seen during each of the past three years. Arctic sea ice extent has been relatively stable during the past decade or so albeit consistently at below-normal levels. This recent uptick in Arctic sea ice volume relative to prior years and the relative stability over the past decade or so in sea ice extent is related to long-term temperature trends in the Arctic region. Specifically, despite the fact that Arctic temperatures have often run at above-normal levels in the cold season during recent years, they have usually been running at nearly normal levels during the all-important summer melting season. Above-normal temperatures during the cold season in the Arctic are usually well below freezing which minimizes the overall impact on the melting of sea ice. The summer season is when temperatures are typically slightly above the freezing mark and any sustained warmer-than-normal conditions during those particular months would likely have an important impact on sea ice; however, this scenario has not been happening for many years.
Graph showing daily Arctic sea ice extent since June 2002 which has been relatively stable in the most recent ten years or so, by courtesy of Japan Aerospace Exploration Agency (JAXA). The IARC-JAXA Information System is a geoinformatics facility for satellite image analysis and computational modelling/visualization in support of international collaboration in arctic and global change research at the International Arctic Research Center (IARC) in corporation with the Japan Aerospace Exploration Agency (JAXA) and the Advanced Earth Science and Technology Organization of Japan (AESTO). The thin blue line indicates the daily Arctic sea ice extent, while the thick line indicates the running 365 day average sea ice extent. Last day shown: 11 July 2018. Credit: climate4you.com
Calculated Arctic sea ice volume as of 28 July 2018 right near the 2014 level (solid red line) and above the 2004-2013 mean level (solid dark gray line) and standard deviation (light gray band). Also, the current level is noticeably higher than the previous three years at this same time of year. The sea ice volume figures are based on calculations using DMI's operational ocean and sea ice model HYCOM-CICE.
Source: Danish Meteorological Institute (DMI).
Recent temperature trends in the Arctic
Actual temperatures in the Arctic were consistently running at above-normal levels during the winter and spring season of this year, but have been generally nearly normal during the all-important summer melting season and this follows long-term trends. In fact, the temperatures in the Arctic region have typically been nearly normal during the summer melting season going all the way back to last century despite generally featuring above-normal conditions during the cold months of the year.
Each of the past six years have featured nearly normal temperatures in the Arctic region during the summer ice melting season and generally above-normal temperatures in the other (cold) months of the year. Source: Danish Meteorological Institute (DMI), ECMWF (Arctic temperatures generated by using initialization data of the operational Euro model).
The Atlantic Multidecadal Oscillation (AMO) and its relationship to Arctic sea ice
Meteorologists track oceanic temperature cycles in the northern Atlantic Ocean through an index value known as the Atlantic Multidecadal Oscillation (AMO). The AMO flipped from negative-to-positive in the mid 1990's signaling an important long-term sea surface temperature phase shift from cold-to-warm and Arctic sea ice extent has generally been below-normal since then. Typically, oceanic temperature cycles in the Atlantic Ocean have lasted for about 20 to 30 years. The Arctic sea ice extent is likely to return to pre-mid 1990’s levels when the oceanic cycle flips back to a cold phase.
The observed Atlantic Multidecadal Oscillation (AMO) index is shown here back to the year 1870. There was an important phase shift in the AMO from cold-to-warm in the mid 1990’s (indicated by arrow). The AMO index is depicted here as the de-trended 10-year low-pass filtered annual mean area-averaged SST anomalies over the North Atlantic basin (0°N-65°N, 80°W-0°E) using HadISST dataset (Rayner, et al., 2003) for the period 1870-2015. Map courtesy NOAA/NCAR
Dramatic recent cool down in the Atlantic Ocean
One of the most important stories in recent weeks in the world of weather and climate has been the abnormally cold waters of the northern Atlantic Ocean. There has been a colder-than-normal patch of water just south of Greenland for several weeks now as well as a large stretch of colder-than-normal water across the tropical Atlantic. These are signs that there may indeed be a long-term phase shift underway or coming soon in the Atlantic Ocean, but it is just too early to say if this is the true start of a sustained changeover or just a false start.
Sea surface temperatures have dropped considerably in recent months relative to normal across much of the North Atlantic (circled region). It is still a bit early to conclude that this dramatic cool down is the beginning of a long-term cold (negative) phase – stay tuned. Credit: NOAA, tropicaltidbits.com
The impact of oceanic cycles and water vapor on Arctic temperatures
The rather consistent temperature trend in the Arctic featuring above-normal temperatures during the Arctic cold (and dry) season and near normal to below normal levels in the summer (more absolute humidity) season suggests water vapor may be playing a critical role. Water vapor is a critical greenhouse gas and even a small increase in the atmosphere can have a (positive) impact on temperatures in the very cold and dry air masses of the Arctic winter where moisture content is extremely low. In recent years, oceans around the world including in the nearby North Atlantic have been generally running at warmer-than-normal levels and this can result in the release of water vapor into the atmosphere. This uptick in water vapor, in turn, may very well be resulting in the usually seen warmer-than-normal conditions during the Arctic cold season when the air is extremely dry. However, an uptick in water vapor would have less of an impact on temperatures during the summer season when there are typically higher levels of moisture in the atmosphere and as long as the summer melting season features normal-to-below normal temperatures, Arctic sea ice volume and extent should stay relatively stable.
Meteorologist Paul Dorian
Perspecta, Inc.
perspectaweather.com
Video discussion on the big turnaround in sea surface temperatures in the North Atlantic: