The average global temperature during the last Ice Age 20,000 years ago was 46°F (7.7°C) — 11°F (6°C) colder than today — a study has reported.
Researchers from the US combined data from tiny marine fossils with climate models to forecast the weather during the so-called Last Glacial Maximum (LGM).
During this chilly period, the Earth’s ice sheets and glaciers had spread to cover around half of Europe, North America and South America — and much of Asia.
According to the researchers, the difference in the average temperatures between the last Ice Age and now represents a ‘huge change’.
The findings will help experts understand the link between changes in atmospheric carbon levels and global temperature shifts — and predict future climate change.
The average global temperature during the last Ice Age 20,000 years ago was 46°F (7.7°C) — 11°F (6°C) colder than today — a study has reported. Pictured, a map of air temperatures during the last glacial maximum in comparison with those of before the industrial period
‘We have a lot of data about this time period because it has been studied for so long,’ said paper author and geoscientist Jessica Tierney of the University of Arizona.
‘But one question science has long wanted answers to is simple: How cold was the ice age?’
To answer this question, Professor Tierney and colleagues analysed the fossilised remains of tiny ocean plankton — which preserve evidence of sea-surface temperatures at the times at which they were alive.
They then combined this data with climate simulations of the Last Glacial Maximum using a technique also employed by weather forecasters, called ‘data assimilation’.
‘What happens in a weather office is they measure the temperature, pressure, humidity and use these measurements to update a forecasting model and predict the weather,’ Professor Tierney said.
The team, she added, used a National Center for Atmospheric Research, Colorado, model ‘to produce a hindcast [or historical forecast] of the LGM, and then we update this hindcast with the actual data to predict what the climate was like.’
Researchers from the US combined data from tiny marine fossils with climate models to forecast the weather during the so-called Last Glacial Maximum (LGM). During this chilly period, the Earth’s ice sheets and glaciers (like that pictured) had spread to cover around half of Europe, North America and South America — and much of Asia
As well as predicting the average global temperatures, the researchers also created maps to show how figures varies in different regions of the world.
She and her team also created maps to illustrate how temperature differences varied in specific regions across the globe.
‘In North America and Europe, the most northern parts were covered in ice and were extremely cold. Even here in Arizona, there was big cooling,’ Professor Tierney said.
‘But the biggest cooling was in high latitudes, such as the Arctic, where it was about 14°C (25°F) colder than today.’
‘Climate models predict that the high latitudes will get warmer faster than low latitudes,’ Professor Tierney added.
‘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.’
With their initial study complete, the team are looking to apply a similar hindcast technique to recreate the conditions experienced in Earth’s warmer periods.
‘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,’ explained Professor Tierney.
This, she added, could ‘improve our understanding of what future climate change might hold.’
Knowing the temperatures of the Earth during the Last Glacial Maximum allows researchers to get a better idea of the climate sensitivity — or, in other words, how much the global temperature changes in response to atmospheric carbon.
The team concluded that, for every doubling of the level of carbon in the atmosphere, the global temperature is liable to rise by 6.1°F (3.4°C) — a figure roughly in the middle of the range predicted by the latest climate models.
During the last ice age, atmospheric carbon dioxide levels were at around 180 parts per million — but today they have increased to 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,’ said Professor Tierney.
‘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.’
‘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.’
The full findings of the study were published in the journal Nature.