Climate variability

Researchers compare global temperature variability during ice ages and interglacials – sciencedaily


Based on a unique global comparison of data from core samples taken from the ocean floor and polar ice caps, AWI researchers have now shown that although climate change has indeed diminished in the world between ice ages and interglacials, the difference is by no means as pronounced as previously assumed. Until now, it was believed that ice ages were characterized by extreme temperature variability, while interglacial periods were relatively stable. Researchers publish their advanced findings online in the journal Nature.

If you want to know how the climate will change in the future, you have to look at the past. By looking at the climate changes that took place thousands of years ago, we can improve predictions for the future climate. Comparing layers of ice core samples and ocean sediments allowed researchers to infer, for example, how the average temperature on Earth has changed over time, as well as the extent of variability. From the height of the last Ice Age 21,000 years ago to our current interglacial period, the Earth has warmed by an average of five degrees Celsius. In view of future global warming, it is vital for today’s global population to know whether temperatures will rise steadily or whether there will be sudden and significant fluctuations. The frequency of extreme events is an essential benchmark for climate change adaptation measures, because when it comes to flood protection, transport and building materials, we need to prepare for the worst-case scenario, and not just “medium” changes.

Climatology researchers from the Helmholtz Young Investigators Group ECUS at the Alfred Wegener Institute Helmholtz Center for Polar and Marine Research (AWI) in Potsdam have now investigated how temperature variability has changed as the Earth has warmed over the past period glacial to the present interglacial period. Temperatures to date have been assumed to vary considerably during the last glacial, while the current interglacial was largely characterized by small variations in temperature. This interpretation was based on water isotopic data from ice cores from central Greenland.

The team, led by Dr Kira Rehfeld and Dr Thomas Laepple, compared data from Greenland with those from sediments collected from several ocean regions around the world, as well as from ice core samples collected in the Antarctic. They demonstrate that the phenomenon of large temperature fluctuations during ice ages was by no means manifested uniformly throughout the world, but rather varied from region to region. For example, in the tropics, temperature variations were three times more intense than today at the height of the last ice age, while ice cores from Greenland show variations 70 times more intense. “Greenland ice cores are undoubtedly an important key to understanding the climate of the past. That being said, our study confirms that the conclusions for Greenland are not always representative of the whole world, ”explains Laepple, leader of the Young Investigators Group. , who also heads the ERC-funded SPACE group of young researchers.

The feat of first author Kira Rehfeld and colleagues: for the first time they gathered and compared data from various climate archives and a total of 99 research sites. In the climate research community, ice cores are generally considered the gold standard because their layers are very cohesive, unlike layers of sediment on the seabed, which are frequently marred by tectonic changes, currents or marine organisms. AWI researchers have developed mathematical methods that allow them to estimate uncertainties and potential sources of error when evaluating various paleoclimate records, and to take these factors into account in their analyzes. “As such, we can compare sediment samples with ice cores for different epochs in the history of the planet,” says Laepple.

The more intense variations during ice ages are due to the greater temperature difference between the ice-covered polar regions and the tropics, which produced a more dynamic exchange of hot and cold air masses. “If we then follow this idea to its logical conclusion, it tells us that the variations will continue to decrease as global warming progresses,” says Rehfeld, simply because the temperature difference between the north and the warming tropics will decrease. “However, our data covers time periods spanning centuries and millennia – we can’t zoom in on just a handful of years, which means we can only draw indirect conclusions about the extreme events that shape time,” explains climatologist Rehfeld, who is currently pursuing research with the British Antarctic Survey (BAS).

Climate modelers had previously postulated the mechanism of reduced variability under warmer climate conditions in 2014. Yet, with their analysis, Rehfeld, Laepple and colleagues are the first to bolster this theory with global climate data from the past. AWI researchers describe their next effort as follows: “We plan to study in detail changes in short-term variations in the past and their relationship to long-term climate change. To do this, we need reliable climate records and to improve our understanding of how they work. ”Increasing accuracy to a level at which paleo-records can also reflect extreme events will likely be one of the greatest challenges for researchers. years to come.