Greenland’s Fate Depends on How Quickly We Can Lower Global Temperatures

Greenland is home to the world’s second-largest ice sheet, which covers about 80% of the island and holds enough water to raise global sea levels by about seven metres. But what will happen to this massive ice sheet if we fail to limit global warming to 1.5 °C above pre-industrial levels, as agreed in the Paris Agreement? And what if we manage to lower the temperatures after overshooting this target?

A new study published in the journal Nature explores these questions and shows that the worst-case scenario of ice sheet collapse and sea-level rise can be avoided – and even partly reversed – if we manage to reduce the global temperatures projected for after 2100.

Greenland’s Fate Depends on How Quickly We Can Lower Global Temperatures
Greenland’s Fate Depends on How Quickly We Can Lower Global Temperatures

The Greenland Ice Sheet is Highly Sensitive to Climate Change

The Greenland ice sheet is losing more than 300 billion cubic metres of ice per year, currently driving global sea levels up by a little less than a millimetre per year. This ice loss is mainly caused by increased surface melting and runoff, as well as enhanced ice flow and calving of icebergs into the ocean.

One of the major concerns is that further warming could trigger feedback processes that amplify the ice loss and make it irreversible. For example, as the air warms, more ice melts, lowering the elevation of the ice surface and exposing it to warmer air temperatures and more melting. This is known as the elevation feedback.

Another feedback process involves the albedo, or reflectivity, of the ice surface. As more ice melts, it exposes darker areas of bare rock or sediment, which absorb more solar radiation and heat up the surface, leading to more melting. This is known as the albedo feedback.

These feedbacks could push the ice sheet past critical thresholds, or tipping points, beyond which it would be impossible to stop or reverse its decline. Scientists estimate that these thresholds could be crossed if global warming exceeds 1.5 °C to 2 °C above pre-industrial levels.

Computer Models Can Simulate How the Ice Sheet Responds to Warming

To predict how the Greenland ice sheet will respond to future warming, researchers use computer models that simulate the physical processes that govern its behaviour. These models divide the ice sheet into thousands of segments and calculate how each segment changes over time, based on factors such as climate change, ice thickness, ice slope, and the temperature of the ice interior and base.

However, these projections are subject to uncertainties, as some of these factors are difficult to measure or predict. For example, it is hard to know exactly how the ice moves over the bedrock, or how the atmospheric and oceanic circulations will change over thousands of years.

To account for these uncertainties, a team of researchers led by Nils Bochow of the Arctic University in Norway used two independent state-of-the-art computer models that were able to simulate how the Greenland ice sheet would respond to various scenarios of global warming over tens of thousands of years.

The Study Shows That Reducing Temperatures After 2100 Can Save Greenland

The researchers considered scenarios where global temperatures peak at different levels above 1.5 °C and then stabilise or decline to lower levels by 2300. They found that if temperatures peak at 2 °C or higher and remain there, then the models predict substantial ice sheet collapse and sea-level rise after several thousands of years.

However, if warming is mitigated after 2100 and temperatures are brought back down to 1.5 °C or lower by 2300, then the models show that the ice sheet can survive and even partially recover. The lower and sooner the temperatures fall, the more chance there is of minimising the ice loss and sea-level rise.

The study also shows that reducing temperatures after 2100 can prevent crossing some of the tipping points that would otherwise lead to irreversible ice sheet decline. For example, one of these tipping points is when the area of the ice sheet exposed to summer melting exceeds 45%. The models show that this can be avoided if temperatures are lowered below 1.5 °C by 2300.

The Study Highlights the Importance of Climate Action

The study provides some hope that Greenland’s fate is not sealed yet, and that we can still prevent or limit its contribution to sea-level rise by taking action to reduce greenhouse gas emissions and lower global temperatures. However, this does not mean that we can relax our efforts to meet the Paris Agreement goals.

As the authors point out, their study does not account for some of the uncertainties and complexities that could affect the ice sheet’s response to warming, such as changes in snowfall, cloud cover, or ocean circulation. Moreover, their scenarios assume that warming is gradually reversed after 2100, which may not be realistic given the current trends and challenges of climate action.

The study also highlights the urgency of meeting the Paris Agreement goals, as the longer we delay, the more likely we are to overshoot the 1.5 °C target and trigger irreversible changes in the ice sheet. Even if we manage to lower temperatures later, the damage done by higher temperatures may not be fully undone.

As the authors conclude, “Our results imply that even if global warming were reversed to pre-industrial levels or below, the Greenland ice sheet would not regrow to its original state within a foreseeable future. Therefore, rapid near-term mitigation is essential to limit Greenland ice sheet mass loss and associated sea-level rise.”

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