8:00 AM | *The Arctic is experiencing yet another summer ice melting season with normal temperatures*
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.
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.
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.
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.
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
Video discussion on the big turnaround in sea surface temperatures in the North Atlantic: