“But even if this target is met,” he added, “sea level rise is likely to accelerate to rates that are very difficult to adapt to.”
Some 230 million people live on land within one metre (3.2 feet) of sea level, and more than a billion reside within 10 metres.
The 2015 Paris climate treaty calls for capping global warming at “well below” 2°C, and 1.5°C if possible.
“If you want to slow sea level rise from ice sheets, you clearly have to cool back from present-day temperatures,” Stokes told AFP.
“To slow sea level rise from ice sheets to a manageable level requires a long-term temperature goal that is close to +1°C, or possibly lower.”
Even if countries defy the odds and keep global warming to the ambitious 1 to 5 degrees Celsius target, rising seas will put humanity’s resilience to the test in the second half of the twenty-first century and beyond, researchers said Tuesday.
According to a study, the rate of ocean-level rise has doubled in the last three decades and is expected to double again by 2100, reaching a rate of roughly one centimeter per year.
Chris Stokes, the lead author and professor at Durham University in England, told AFP that “limiting global warming to 1.5°C would be a major achievement” and prevent many negative climate effects.
“But even if this target is met,” he continued, “the rate of sea level rise is likely to accelerate to levels that are extremely challenging to prepare for.”. “.”.
Previous studies have indicated that if sea walls and other protective measures are not implemented, an extra 20 centimeters (7.8 inches) of sea level rise by 2050—the width of a letter-sized sheet of paper—would result in approximately $1 trillion in flood damage every year in the 136 largest coastal cities worldwide.
Approximately 230 million people reside on land that is one meter (3.02 feet) above sea level, and over a billion people live within ten meters.
The melting of mountain glaciers and ice sheets, as well as the growth of warming oceans that absorb over 90% of the excess heat brought on by climate change, are the two main causes of sea level rise.
In the journal Communications Earth and Environment, Stokes and colleagues pointed out that the Earth’s surface temperature is currently 1 to 2 degrees Celsius warmer than it was before industrialization, which is already sufficient to raise the ocean watermark by several meters over the ensuing centuries.
By the end of the century, global temperatures are expected to increase by 2 to 7°C.
Tipping points.
Stokes and his team reviewed the scientific literature since the last major climate assessment by the Intergovernmental Panel on Climate Change (IPCC), which is mandated by the UN. They concentrated on the increasing role of ice sheets in sea level rise.
Depending on how quickly humanity reduces greenhouse gas emissions, the IPCC gave a “likely” sea level rise of 40 to 80 centimeters by 2100 in 2021. However, because of uncertainty, they did not include ice sheets in their models.
Since then, the picture has become much clearer.
“We are most likely moving toward the higher numbers in that range, if not higher,” Stokes stated.
Starting with what has been observed and measured thus far, the scientist and his team examined three baskets of evidence.
With enough frozen water to raise oceans by about 65 meters, satellite data has shown that ice sheets are far more vulnerable to climate change than previously thought.
Over the past three decades, the amount of ice that melts or breaks off into the ocean from West Antarctica and Greenland has quadrupled, surpassing runoff from mountain glaciers. It currently averages about 400 billion tonnes annually.
Estimates of the amount of global warming required to push diminishing ice sheets past tipping points—points beyond which they can no longer be recovered—have also changed.
According to Stokes, “we used to think that Greenland wouldn’t do anything until the world warmed 3°C.”. “Right now, 1 to 5°C is thought to be the tipping point for West Antarctica and Greenland. “,”.
The 2015 Paris Climate Accord aims to keep global warming “well below” 2°C, and ideally between 1 and 5°C.
With similar temperatures and atmospheric concentrations of CO2, the primary cause of global warming, the scientists also examined new data from the three most recent epochs in Earth’s history.
Even though the average global temperature was slightly lower and there was much less CO2 in the air (287 parts per million compared to 424 ppm today), sea levels were two to nine meters higher than they are today, roughly 125,000 years ago, during the previous “interglacial” between ice ages.
Oceans were 6–13 meters higher during a slightly warmer time 400,000 years ago, when CO2 concentrations were around 286 parts per million.
Additionally, sea levels were 10–20 meters higher three million years ago, which is when CO2 levels were at their lowest point in Earth’s history.
In conclusion, researchers examined current forecasts regarding the future behavior of ice sheets.
Stokes told AFP, “It is obvious that you need to cool back from current temperatures if you want to slow sea level rise from ice sheets.”.
“A long-term temperature goal of about +1°C, or possibly lower, is necessary to slow sea level rise from ice sheets to a manageable level. “..”.
