Climate change and extreme weather linked to high pressure over Greenland
By John Cappelen, DMI
April 27th 2016
- Climate change and extreme weather – including extreme weather patterns over northwest Europe – linked to high pressure weather systems over Greenland
- Study finds increase in atmospheric high pressure systems since 1980s throughout all seasons
- High pressure weather systems drag unusually warm air over Greenland’s Ice Sheet
Greenland is one of the fastest-warming regions of the world. New research from a team of climate change experts led by Professor Edward Hanna at the University of Sheffield has identified changes in weather systems over Greenland that have dragged unusually warm air up over the western flank of Greenland’s Ice Sheet. These weather systems are also linked to extreme weather patterns over northwest Europe. The team also includes climate scientist John Cappelen from the Danish Meteorological Institute.
Blocking over Greenland
The study analysed changes in weather systems over Greenland since 1851, using a measure called the Greenland Blocking Index (GBI). The index measures the occurrence and strength of atmospheric high pressure systems, which tend to remain stationary when they occur, causing long runs of relatively stable and calm weather conditions. The high pressure also blocks storm systems from moving in on the region. The previous available version of the GBI only extended back to 1948.
The team of climate change experts have found an increase in the occurrence of atmospheric high pressure ‘blocking’ systems over Greenland since the 1980s throughout all seasons, which relates to a significantly strong warming of the Greenland and wider Arctic region compared with the rest of the world.
The team also found an especially strong recent increase in the occurrence of Greenland ‘blocking’ weather systems in summer, which is linked to a more northward-meandering branch of the atmospheric jet stream. This has resulted in warmer air more often moving north into the region in recent years.
The research has also found an increase in the incidence of high pressure weather systems remaining stationary over Greenland since the 1980s, which is exerting a significant impact on extreme weather and climate change in the region.
Related to sea ice decrease?
These weather systems are occurring in the area more often because of strong Arctic warming and changes in the atmospheric jet stream in recent years.
This is resulting in an increase in the occurrence of warm air in the region and it is also affecting weather systems downstream of Greenland, such as over northwest Europe. Recent wet summers in Denmark, for instance, can be linked to these stationary high pressure systems over Greenland.
The research team found that Greenland ‘blocking’ pressure systems have become much more variable from year to year in December in recent decades. This reflects an increasing destabilisation of atmospheric weather systems in late autumn and early winter, which the team believe may be related, at least in part, to dramatic declines in sea-ice coverage in the Arctic region.
Sea-ice coverage throughout the Arctic has significantly reduced in recent years, which we already know is having an amplifying effect on warming in the region. What this study now tells us is that changes in stationary high pressure over Greenland are adding to the change in polar climate.
This research has more than doubled the timespan of data analysed on Greenland ‘blocking’ weather systems and is a useful measure of changes in North Atlantic atmospheric circulation. The results can enable an improved understanding of the links between mid-latitude and high-latitude climate change when combined with other climatological studies.
Findings from the research are published in the International Journal of Climatology on 27 April 2016
Greenland Blocking Index 1851-2015: a regional climate change signal
Hanna, E., Cropper, T., Hall, R. and Cappelen, J. (2016) Greenland Blocking Index 1851-2015: a regional climate change signal. International Journal of Climatology.
We present an extended monthly and seasonal Greenland Blocking Index (GBI) from January 1851- December 2015, which more than doubles the length of the existing published GBI series. We achieve this by homogenising the Twentieth Century Reanalysis version 2c-based GBI and splicing it with the NCEP/NCAR Reanalysis-based GBI. For the whole time period there are significant decreases in GBI in autumn, October and November, and no significant monthly, seasonal or annual increases. More recently, since 1981 there are significant GBI increases in all seasons and annually, with the strongest monthly increases in July and August. A recent clustering of high GBI values is evident in summer, when seven out of the top eleven values in the last 165 years – including the two latest years 2014 and 2015 - occurred since 2007. Also, 2010 is the highest GBI year in the annual, spring, winter and December series but 2011 is the record low GBI value in the spring and April series. Moreover, since 1851 there have been significant increases in GBI variability in May and especially December. December has also shown a significant clustering of extreme high and low GBI values since 2001, mirroring a similar, recently identified phenomenon in the December North Atlantic Oscillation index, suggesting a related driving mechanism. We discuss changes in hemispheric circulation that are associated with high compared with low GBI conditions. Our GBI time series should be useful for climatologists and other scientists interested in aspects and impacts of Arctic variability and change.
Keywords: Blocking; climate change; GBI; Greenland; NAO; pressure