More than 100,000 years ago, global sea levels rose an estimated 6 to 9 meters (20 to 30 feet) higher than today, with as much as half of that derived from Greenland’s ice sheet melting – an outcome we may see in today’s world given the current state of our rapidly changing climate.
Using marine and terrestrial geological archives, researchers have created a century-by-century timeline of climatic conditions throughout the last 100,000 years. These showed that after an early period of peak warmth, some centuries during the Last Interglacial (between 129,000 and 116,000 years ago) were much warmer than others, resulting in southern Europe experiencing dry spells and cold water spreading through the North Atlantic. This led to a relatively unstable climate that saw “abrupt” changes in oceanic currents, rainfall, and ice melting.
For the study, published in Nature Communications, researchers pulled samples from Greenland ice cores and compared them to both deep-sea sediment samples taken at the Portuguese Margin and to mineral deposits found in a cave in Italy. Together, these samples revealed that certain centuries experienced more rapid sediment buildup than others, indicating periods of higher ice runoff due to a dryer, warmer climate.
“We know from independent evidence that part of the Greenland ice sheet melted during the LIG, contributing higher mean global sea level than present,” lead author Chronis Tzedakis, from University College London, told IFLScience.
Based on these climate model experiments, Tzedakis suggests Greenland’s ice-melt and runoff could have contributed to a weakening of the Atlantic meridional overturning circulation (AMOC), ultimately creating a cooling effect in the North Atlantic and an arid climate in southern Europe.
AMOC is a system of ocean currents in the North Atlantic that act as a conveyer belt to move water and air, essentially influencing weather systems. Previous research indicates climate change is slowing down the Atlantic’s ocean currents by as much as 15 percent since the mid-20th century. This is in part, Tzedakis notes, due to more freshwater entering the North Atlantic from ice melting. Continued warming is expected, which could potentially put our world in a similar scenario of a subpolar North Atlantic and a dry southern Europe.
Today, we’re experiencing a rapid change in climate due to anthropogenic causes. Periods of warming during the LIG, on the other hand, were caused by stronger solar radiation in northern latitudes during the summer months simply because Earth was closer to the Sun. This led to intense Arctic warming with surface air temperatures estimated at 3-11°C above pre-Industrial levels. These temperatures are comparable to high-latitude warming scenarios for the end of this century. Although not caused by humans, dry and cool periods during the LIG are anomalous in that they represent a departure from normal warm interglacial conditions with a strong AMOC.
“So even though it is not a perfect analog for current and future warming caused by greenhouse gas emissions, the LIG can provide insights into climate processes during a period of excess warmth,” explained Tzedakis. “A simple precautionary principle would suggest that curbing anthropogenically-induced global warming, which is expected to be amplified in the Arctic, would be wise.”