How quickly is sea level going to rise? More than 700 million people desperately need an accurate answer.

“For low-lying coastal cities like Lagos, New Orleans, and Bangkok, fast sea level rise could submerge them and displace millions of people, whilst slower sea level rise would give time to adapt,” says Fred Richards.

The 2018 Schmidt Science Fellow and Assistant Professor of Earth Sciences has recently been awarded a €1.5M European Research Council (ERC) grant to improve the accuracy of sea-level forecasts.

Under the worst-case scenario – if the West Antarctic and Greenland ice sheets undergo runaway melting – it is estimated that global sea level could rise by nearly 2m by 2100, threatening dozens of major cities, including London and New York, and obliterating low-lying island nations such as the Marshall Islands in the Pacific Ocean.

But under more moderate scenarios, the rise could be much slower, giving us centuries to prepare, mitigate, and adapt.

How quickly we get a grip on carbon emissions will undoubtedly play a role in which path we follow, but perhaps what is less intuitive is the impact that Earth’s slowly churning mantle and restless crust may play.

This relationship between deep-Earth processes and ice-sheet stability is not well understood.

To address this knowledge gap, Fred’s ERC-supported project – known as Earth2Sea – will reconstruct how the Earth’s mantle has evolved over the last 50 million years and integrate this with past ice sheet data.

“By better constraining mantle movements and ice sheet behaviour from the past, we can better calibrate our ocean and ice sheet models and narrow the uncertainty in their future sea level predictions,” says Fred, who is based at Imperial College London.

Such information is urgently needed by decision makers to better protect the 700 million people living along flood-threatened coasts and the critical infrastructure we all depend on.

Trained as a geophysicist at the University of Cambridge, Fred started his research career by studying how the flow of hot rock within Earth’s interior influenced surface topography.

With the support of Schmidt Science Fellows, he pivoted to environmental science to explore how those same deep-Earth processes interact with Earth’s climate system.

Working backwards from the present day, Fred and colleagues modeled how shallow mantle structure had changed underneath Australia as far back as 3 million years ago – a warm time in Earth’s history and a good analogue for today.

“We used to think that it took thousands of years for the Earth to rebound after an ice sheet had melted, but GPS measurements from Greenland and Antarctica are showing it can happen on annual to decadal timescales”

They found that mantle flow beneath this region had evolved much faster than previously thought, pushing the land up significantly in the past.

Accounting for this vertical motion resulted in lower estimates of sea level 3 million years ago, calling into question some more extreme models of future ice sheet retreat and sea-level rise.

And this is not the only way the deep Earth impacts surface processes.

In 2023, Fred received a Schmidt Science Fellows Catalyst Grant, small-scale funding that supports collaboration between Fellows.

He teamed up with 2019 Schmidt Science Fellow and glacial geomorphologist, Sasha Montelli, to reconstruct the movements of the West Antarctic Ice Sheet and connect them to spatial variations in heat flow from the Earth’s deep interior.

“Ice sheets flow much faster if there is a lubricating layer of water at their base, allowing them to slide along the bedrock,” explains Fred. “Heat flow dictates whether the ice sheet’s base is frozen onto the bedrock or melted and moving.”

The early findings from the Catalyst Grant work influenced the objectives of the ERC project.

Another process that seems to act on shorter timescales than previously thought is glacial isostatic adjustment: the way the Earth and sea surface deforms in response to changing ice and water loads.

“We used to think that it took thousands of years for the Earth to rebound after an ice sheet had melted, but GPS measurements from Greenland and Antarctica are showing it can happen on annual to decadal timescales,” says Fred.

And if rebound does occur quickly, in the future it could lift the West Antarctic and Greenland ice sheets out of the water more rapidly, reducing the area in contact with warm seawater and slowing the rate of melt and retreat.

Understanding the interplay between these different processes and the timescales over which they operate is key to the Earth2Sea project.

Collaborating with colleagues in the UK, Canada, and Australia, Fred will reconstruct mantle movements and heat flow changes over the last 50 million years.

The aim is to produce reliable sea-level projections that can capture regional and local level variations as well as globally averaged trends.

For example, in Greenland sea level will fall as the ice melts and the land rebounds, whereas small island nations in the Pacific will see above-average sea-level rise.

“These are extreme examples, but refining these local effects is key, and at the moment we can’t do it very well,” says Fred.

It is an ambitious and important project that could improve the future of coastal communities worldwide.

Fred’s team aims to produce its first sea-level projections within five years.