We now know how much emissions have delayed the next glacial period
Changes in Earth’s orbit drive long-term glacial cycles, but a new forecast suggests this ancient pattern is being disrupted for tens of thousands of years due to human-induced global warming
By James Dinneen
27 February 2025
Earth during a glacial period
Zoonar/Alexander Savchuk/Alamy
Without human-induced climate change, Earth may have been on track to plunge into another glacial period within 11,000 years. This long-term forecast of the planet’s “natural” climate is based on a new analysis of how wobbles in the shape of its orbit and the tilt of its axis combine to change the amount of solar energy reaching the planet.
For millions of years, these orbital oscillations – known as Milankovitch cycles – brought the planet in and out of glacial periods about every 41,000 years. But the past 800,000 years have seen these glacial cycles, also known as ice ages, occur only every 100,000 years or so. The term ice age can be used to refer to any time there was ice at Earth’s poles, as there is now, though it is also commonly means periods of widespread glaciation.
Ambiguities in the record of when ice sheets advanced and retreated meant it wasn’t possible to explain how orbital changes were involved in driving this longer cycle, a mystery known to palaeoclimatologists as the “100 thousand year problem”.
Advertisement
Read more
Is climate change accelerating after a record year of heat?
Where previous studies tried to link changes in orbit to specific periods like the onset of an ice age, Stephen Barker at Cardiff University, UK and his colleagues took a new tack. They looked at the overall patterns of how glacial periods, also called ice ages, fade and return during the intervening “interglacials”. This enabled them to link changes in orbit with changes in ice – despite fuzziness in the ice record over the past million years.
They found these 100,000-year cycles appear to follow a straightforward rule. For the past 900,000 years, every interglacial has occurred after Earth’s axis wobbled at its furthest point from the sun as the planet was also tilting closer towards the sun, following the most circular phase of its orbit.
