Climate Denial Crock of the Week

Copernicus Climate Change Service:

• In September 2022, Greenland experienced exceptional heat and rainfall as a result of a series of atmospheric rivers, which are long bands of moisture transport in the atmosphere.
• Temperatures in September were the highest on record; up to 8°C higher than average.
• Rainfall was much higher than average across southern and western areas of the ice sheet. An area in the far southwest saw almost double the average amount of rainfall for September, a time of year when snowfall is more typical.
• The ice sheet saw record melt, with at least 23% of its area impacted at the peak of the first heatwave.
• Since the late 1990s, there has been an increase in the frequency of atmospheric rivers reaching Greenland.

Greenland’s melt season typically occurs between May and the end of August each year, so in September, the melting has usually finished for the year. However, Greenland’s climate conditions in September 2022 were far from usual.

A persistent and strong atmospheric circulation pattern connected a series of atmospheric rivers to Greenland from the subtropical and mid-latitude Atlantic. Atmospheric rivers can transport large amounts of warm, moisture-laden air poleward from the warmer lower latitudes. Together with generally more moist atmospheric conditions resulting from a warming climate, this makes heavy precipitation more likely.

Large amounts of precipitation are often produced when these atmospheric rivers reach land. The high temperatures and moisture associated with such events in September 2022 contributed to record levels of ice sheet melt.

There was also an extreme ‘piteraq’ towards the end of the month, with wind gusts above 180 km/h, leading to evacuations and damage to buildings.

September 2022 was the warmest on record for Greenland, based on multiple datasets with records going back at least 73 years. Average temperatures for the month reached up to 8°C higher than average for the 1991–2020 reference period in central areas, with temperatures over the ice sheet as a whole close to 6°C above average.

These exceptionally warm conditions were brought about by three heatwaves connected to atmospheric rivers. The most intense heatwave spanned 2–6 September, followed by another from 10–16 September and a third from 23–28 September.

During these heatwaves, temperatures were above freezing at several locations on the Greenland ice sheet. For example, a high altitude (2883 m elevation) automated weather station at the southern dome of the ice sheet recorded 39 hours with temperatures above 0°C. Previously, the only periods with temperatures above 0°C at this station were much shorter: four hours in 2003 and one hour in 2016. Another location^[3], in western Greenland, saw 325 hours with temperatures above 0°C during September. Here, melt had occurred in 18 previous years out of a 28-year record, for an average of 57 hours. The exceptional heat further impacted the ice sheet by reducing the snow albedo by up to 15%. Ice crystals vary in shape and the heat rounds the otherwise sharp ice crystal edges, reducing their albedo and accelerating melting.

In Greenland, the melting season generally lasts from May to August. During September, temperatures are typically below freezing and precipitation falls as snow, the beginning of the snow accumulation season that continues to May. In 2022, a period of record-breaking heatwaves and precipitation that fell as rainfall more often than as snow, led to the most extensive September surface melting of the ice sheet on record^[5]. On 3 September, at least 23%^[6] of the Greenland ice sheet had surface melt – an area of at least 442,000 km².

These heatwaves brought melt conditions that pushed the snow line inland and up the ice sheet, exposing a wider area of bare ice. Satellite images captured in late September show the typical return of snow cover in 2020 and the abnormally persistent bare ice conditions at lower elevations in 2022.

During September 2022, three atmospheric rivers reached Greenland, delivering heat and moisture from the North Atlantic, bringing much warmer-than-average temperatures and precipitation that fell as rain rather than snow. Rainfall reached elevations well above 2000 m across the south and west part of the ice sheet, with large rainfall anomalies across this region. Rainfall above 2000 m is rare over the Greenland ice sheet, even during summer^[7]. Total monthly rainfall peaked close to 350 mm on the south-southwestern ice sheet (Figure 5), which is almost double the average amount of rainfall for the time of year. Rainfall of more than 150 mm occurred as far north as 76° latitude on the northwestern ice sheet, an area seeing a pronounced trend towards increasing rainfall^[7].