Efforts to limit the global temperature increase to 1.5 degrees under the Paris climate agreement may not go far enough to save the world’s ice sheets from melting and causing profound changes to coastlines, scientists have concluded.
Research led by Durham University in the UK suggests the target should instead be closer to 1 degree to avoid significant losses from polar ice sheets and to prevent further acceleration in sea level rise.
The team reviewed evidence including satellite imagery to examine the effect that the 1.5-degree target would have on immense ice sheets in Greenland and Antarctica, which together store enough ice to raise global sea levels by almost 65 metres.
The mass of ice lost from these ice sheets has quadrupled since the 1990s and they are currently losing about 370 billion tonnes of ice a year, they show – with current warming levels of about 1.2 degrees above pre-industrial temperatures (the mid-19th century) based on the latest United Nations (UN) Intergovernmental Panel on Climate Change report.
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Further warming to 1.5 degrees – on a 20-year average – “would likely generate several metres of sea level rise over coming centuries as ice sheets melt in response to both warming air and ocean temperatures”.
This would make it very difficult and far more expensive to adapt to rising sea levels, “causing extensive loss and damage to coastal and island populations and leading to widespread displacement of hundreds of millions of people”, they conclude.
Policymakers and governments need to be more aware of 1.5-degree rise could have on ice sheets and sea levels, said the researchers.
Currently, about 230 million people live within one metre of sea level and melting ice represents an existential threat to those communities, including several low-lying countries, they said.
Avoiding this would require a global average temperature cooler than that of today, which the researchers suggest is closer to 1 degree above pre-industrial levels – or possibly even lower.
The research, including inputs from other experts in the UK and US, was published in Communications Earth and Environment on Tuesday.
“We’ve known for a long time some sea level rise is inevitable over the next few decades to centuries, but recent observations of ice sheet loss are alarming, even under current climate conditions,” said lead author Prof Chris Stokes.
“Limiting warming to 1.5 degrees would be a major achievement and this should absolutely be our focus. However, even if this target is met or only temporarily exceeded, people need to be aware sea level rise is likely to accelerate to rates that are very difficult to adapt to – rates of one centimetre per year are not out of the question within the lifetime of our young people”.
“We are not necessarily saying all is lost at 1.5 degrees, but we are saying every fraction of a degree really matters for the ice sheets – and the sooner we can halt the warming the better, because this makes it far easier to return to safer levels further down the line,” he said.
“We only have to go back to the early 1990s to find a time when the ice sheets looked far healthier,” Prof Stokes said.
Global temperatures were about 1 degree above pre-industrial times back then and carbon dioxide concentrations were 350 parts per million, which others have said is a much safer limit for Earth. Carbon dioxide concentrations are currently around 424 parts per million and continue to increase.
Co-author Prof Rob DeConto of University of Massachusetts Amherst said that even if the Earth returns to its pre-industrial temperature, it will still take hundreds to perhaps thousands of years for ice sheets to recover.
“If too much ice is lost, parts of these ice sheets may not recover until the Earth enters the next ice age. In other words, land lost to sea level rise from melting ice sheets will be lost for a very, very long time. That’s why it is so critical to limit warming in the first place,” he said.
