Sea levels could rise by a metre by 2100, according to the latest landmark UN report which warns that many serious impacts of climate change are already inevitable, whether emissions are curbed or not.
Already 1C of warming has made the oceans hotter and more acidic, while melting glaciers and ices sheets are causing sea levels to rise at worrying rates, scientists say.
Extreme surges and flooding events that occur once a century could happen every year by mid-century, according to experts behind the latest Intergovernmental Panel on Climate Change (IPCC) report. Hundreds of millions of people worldwide who live in low-lying coastal areas, from villages to megacities, will experience more intense tropical cyclones and storms, extreme storm surges and flooding.
In the report, more than 100 authors from 36 countries drew on around 7,000 scientific publications that looked at two major elements of the climate – the oceans and the cryosphere, or frozen areas.
“With increasing climate change, it is becoming extremely hard for the planet to retain its naturally-occurring reservoirs of ice – known to climate scientists as the cryosphere,” said Dr Helene Hewitt, head of the Ocean Modelling group at the Met Office.
“Meltwater from glaciers and ice sheets entering the ocean has now become the dominant source of global sea level rise, overtaking the thermal expansion of water as the principal driver of rising sea levels.
“Under all greenhouse gas emission scenarios, sea levels are expected to continue rising. Although projections show there is an obvious reduction in rise following the greatest cuts in emissions.”
Several metres of sea-level rise is predicted for 2300 in a high-emissions world, meaning billions of people would be displaced.
Annual coastal flood damages are projected to increase 100 to 1,000 times by 2100, and some island nations are “likely to become uninhabitable”.
While sea level has risen globally by around 15cm during the 20th century, it is currently rising more than twice as fast, at 3.6mm per year, and speeding up as Greenland and Antarctic ice sheets melt.
Sea levels could rise by around 30cm to 60cm by 2100 even if greenhouse gases are rapidly cut and global warming is kept to well below 2C above pre-industrial levels, but around 60-110cm if emissions continue to increase, the study said.
“The result is that ice is going to disappear faster than ever: some mountain regions such as the Alps could be almost completely deglaciated by 2100,” said Professor Jonathan Bamber, director of the Bristol Glaciology Centre at the University of Bristol.
“Sea level rise is projected to continue whatever the emission scenario and for something like business-as-usual the future for low lying coastal communities looks extremely bleak. The consequences will be felt by all of us.”
The report also says marine heatwaves have very likely doubled in frequency since 1982 and are increasing in intensity. Wildfires are set to increase across the tundra and cold northern forests, as well as some mountain regions.
The oceans have helped limit the impact of greenhouse gases so far, absorbing much of the extra heat and carbon dioxide, but that has affected the survival of fish stocks and wildlife such as corals, a situation set to worsen.
And the melting permafrost contains large stores of greenhouse gases which could be released into the atmosphere as the frozen ground thaws, adding to global warming.
Professor Peter Wadhams, professor of ocean physics at the University of Cambridge, said the report did not mention the “very serious threat” of methane coming from the seabed of the Arctic continental shelf as its permafrost thaws – which could release large amounts of the greenhouse gas.
The latest report comes after a major study from the UN science body last year said unprecedented and rapid action was needed to keep global warming to 1.5C above pre-industrial levels and avoid the worst impacts of climate change.
Hoesung Lee, chairman of the IPCC, said: “The open sea, the Arctic, the Antarctic and the high mountains may seem far away to many people.
“But we depend on them and are influenced by them directly and indirectly in many ways – for weather and climate, for food and water, for energy, trade, transport, recreation and tourism, for health and wellbeing, for culture and identity.
“If we reduce emissions sharply, consequences for people and their livelihoods will still be challenging, but potentially more manageable for those who are most vulnerable.”
Nearly half of the world’s coastal wetlands, which protect from erosion and flooding and are important carbon stores, have been lost over the last 100 years, as a result of human activity, sea level rises, warming and extreme events.
Urgent and ambitious emissions reductions are needed alongside coordinated, sustained and increasingly ambitious action to help people adapt to the changes that are taking place, researchers found.
Rod Downie, chiefpolar adviser at WWF, said: “I like to think of ice as one of humanity’s best investments. It’s a bit like having capital in your bank account. And we want it to stay there.
“We want the ice to remain in the polar regions. But instead we’re eating into it, we’re dissolving it. We’re spending that capital and that has really dramatic consequences for people in the Arctic, and for people across the world, including here in the UK.”
Additional reporting by PA
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