Researchers combined fossil data with climate simulations to find out exactly how cold the Last Glacial Period was 20,000 years ago.
A study led by the University of Arizona estimates that Earth’s average temperature during the Last Glacial Period (approximately 20 thousand years ago) was 7.8ºC.
Recently published in the journal Nature, the article may help climatologists better understand the relationship between the average global temperature and the current increase in carbon dioxide in the atmosphere.
According to the study’s results, the average global temperature during the Ice Age was 6 ºC colder than that of the last century, which was 14 ºC.
“In your own personal experience that might not sound like a big difference, but, in fact, it’s a huge change,” said Jessica Tierney, associate professor in the UArizona Department of Geosciences and the study’s lead author.
According to Tierney, although the Last Glacial Period has been extensively studied, finding out exactly what the temperature was at that time was still a challenge.
To put an end to this mystery, she and her team developed a model capable of deducing sea-surface temperatures based on data from plankton fossils.
Using a data assimilation technique, they combined the fossil information with models of climate simulations of the time.
The Last Glacial Maximum was characterized by the formation of large glaciers that covered half of North and South America, as well as Europe and parts of Asia.
“But the biggest cooling was in high latitudes, such as the Arctic, where it was about 14 C (25 F) colder than today,” Tierney said. At that time, flora and fauna that were adapted to low temperatures thrived.
The article’s conclusions are compatible with what is known about how the poles react to temperature changes.
“Climate models predict that the high latitudes will get warmer faster than low latitudes,” Tierney explained. “When you look at future projections, it gets really warm over the Arctic. That’s referred to as polar amplification. Similarly, during the LGM, we find the reverse pattern. Higher latitudes are just more sensitive to climate change and will remain so going forward.”
The researchers intend to use the same models to learn more about the warm periods of the past, providing a clearer picture of the consequences of current global warming.
“If we can reconstruct past warm climates, then we can start to answer important questions about how the Earth reacts to really high carbon dioxide levels, and improve our understanding of what future climate change might hold,” Tierney said.
Studying the past is key to understanding what the future may hold
Knowing the temperature of the last Ice Age is important to broaden our understanding of the sensitivity of the planet’s climate, especially in relation to changes in temperature in response to carbon dioxide in the atmosphere.
According to the new study, for each doubling of atmospheric carbon, the global temperature should increase by 3.4 ºC – a value compatible with the average predicted by other climatic models, which is between 1.8 and 5.6 ºC.
During the Ice Age, carbon dioxide levels were around 180 parts per million, which is very low. Before the Industrial Revolution, they were already at 280 parts per million. Today, there are at 415 parts per million.
“The Paris Agreement wanted to keep global warming to no larger than 2.7 F (1.5 C) over pre-industrial levels, but with carbon dioxide levels increasing the way they are, it would be extremely difficult to avoid more than 3.6 F (2 C) of warming,” Tierney said. “We already have about 2 F (1.1 C) under our belt, but the less warm we get the better, because the Earth system really does respond to changes in carbon dioxide.”