“Fever diagnosis” of a special kind: A study documents how clearly global warming is also affecting the remote highlands in the middle of the Greenland ice sheet. The years 2001 to 2011 were 1.5 degrees Celsius warmer than the 20th century average, according to the analysis of ice cores. It was also the warmest decade in this 1,000-year glimpse of regional climate history. The researchers were also able to link the warming to a significant increase in ice melt in Greenland.
Everywhere in the world, climate change is threateningly noticeable – but a particularly anxious look is directed at the largest island on earth: Because the ice sheet of Greenland, which is up to three kilometers thick, plays an important role in the global climate system and the possible melting of the gigantic ice masses Concrete catastrophe potential: At the current emission rates of greenhouse gases, it is estimated that Greenland alone could contribute 50 centimeters to global sea level rise by the year 2100. The warming there and its consequences are already documented by measurements taken from the Greenland coast. So far, however, it has remained unclear to what extent the areas in the middle of the ice sheet, some of which are over 3000 meters high, are also affected. Because analysis data from ice cores, which were obtained in the 1990s in the region, did not allow any clear conclusions.
But together with the new data that a German-Danish research team is now presenting, a clear picture emerges. They come from analyzes of ice cores that were obtained in the winter of 2011/2012 in the northern area of the central high plateau of Greenland. This is how a reliable climate archive was created, which the researchers say goes back about 1000 years. The detection of stable oxygen isotopes was used to reconstruct the temperature in the layer structures of the drill cores. The scientists explain that their concentrations clearly reflect the temperatures that once prevailed on the high plateau.
Millennium heat record
They found that the reconstructed temperature for 2001-2011 was, on average, 1.7 degrees Celsius warmer than the 1961-1990 period and 1.5 degrees warmer than the entire 20th century. The researchers assume that, in addition to natural fluctuations, these increased values are fundamentally due to the global warming trend that has been emerging since industrialization. A closer look at the icy climate archive makes this clear: In the last thousand years, it has never been as warm on the Greenland plateau as it was between 2001 and 2011. “The warming in this phase clearly differs from the natural fluctuations of the last 1000 years. We feared that in view of global warming, but the clarity and conciseness is unexpected,” says lead author Maria Hörhold from the Alfred Wegener Institute, Helmholtz Center for Polar and Marine Research (AWI).
As part of the study, the team also investigated possible connections between temperatures at high altitudes and meltwater runoff. To do this, the researchers combined their data with information from regional climate models for the period 1871 to 2011 and satellite observations of ice mass change for the years 2002 to 2021. The results illustrated the increase in melting since the 2000s and pointed to connections: “We were amazed at how The temperature in the middle of the ice sheet is closely related to the meltwater runoff across Greenland, which occurs on the coasts, i.e. the edges of the ice sheet,” says Hörhold. According to the researchers, this could help to understand the melting dynamics of the ice sheet and ultimately clarify what we have to be prepared for with sea level rise.
Climatically decoupled
The study has also shown that Greenland is characterized by special climate processes, the researchers report. This emerged from comparisons of the current temperature reconstructions with Arctic-wide data. It became clear that the climatic processes in the island’s ice-covered heights are partially decoupled from the circumpolar regions. “We would have actually expected that the time series would correlate relatively well with the warming of the Arctic region. But our reconstruction of the development of the temperature over Greenland shows its own dynamics,” says senior author Thomas Laepple from the AWI. Apparently, the high altitude of the ice sheet strongly affects atmospheric circulation patterns over Greenland, the researchers explain. According to them, this emphasizes the importance of regionally resolved temperature time series in order to better capture climate change in the far north of the world.
Source: Alfred Wegener Institute Helmholtz Center for Polar and Marine Research, specialist article: Nature, doi: 10.1038/s41586-022-05517-z