Sea levels are rising as climate change warms the atmosphere and oceans, melting ice trapped in the Arctic and Antarctica. But knowing exactly what that means for coastal, marine and island communities, is an urgent question facing science.
Research that Cosmos reported on last week warns that, if global warming is not restricted to 1.8°C, then melting polar ice sheets alone will see sea levels rise around 1.4 metres by the year 2150.
But as Jun-Young Park from South Korea’s Pusan National University, lead author of the study published in Nature Communications says: “A one-metre sea level rise in 2100 CE could threaten more than 400 million people.”
It is these threshold events scientists need to understand to adequately warn people and explain how they should prepare. “If we do not restrict warming to below 1.8 degrees, many cities near the coastal line will be inundated by sea level rise,” says Park.
Park tells Cosmos that “ice sheet melting and corresponding sea level rise will accelerate over several more centuries. This would be clearly an irreversible situation that would challenge future generations.”
“Every 0.1 degree matters and there are thresholds that are critically important.”
“Globally, low-lying Pacific Islands and large estuaries (e.g. in Bangladesh) are most at risk,” head of Monash University’s School of Earth, Atmosphere and Environment professor, Andrew Mackintosh told Cosmos. “Many large cities (e.g. Shanghai, New York) currently lie close to sea level. Wealthier countries will have more capability to adapt to the projected changes.”
“Sea level rise in Australia will cause increased inundation of low-lying areas, coastal erosion and storm surges affecting coastal communities and ecosystems.
“Australia’s population is dominantly located at the coast, and sea level rise of 1.1 m will put more than 200 billion dollars of infrastructure at risk.”
“It’s not just sea level rise that will have a huge impact: when you couple sea level rise with storm surges and high tide it’s a recipe for disaster for coastal environments and society. For reference, the Maldives is on average ~1.2 m above sea level.”
According to McCormack, the 1.8°C threshold refers to a specific emissions scenario – (Shared Socioeconomic Pathway) SSP1-1.9 – used in the latest (Intergovernmental Panel on Climate Change) IPCC report where SSP1 represents a shift towards a sustainable future.
“Temperature thresholds are used to help us to explain the different scenarios in layman’s terms – it’s much easier to understand 1.8 degrees of warming compared with an increase of 2.6 W/m2 of climate forcing,” McCormack notes.
“Ice sheets are inherently a threshold-driven system, so thresholds matter.
“The problem is that we do not know the exact thresholds for ice sheets yet, but studies like these ones help us to get closer to discovering the them.
“What we do know is that crossing thresholds can result in profoundly different outcomes – with staying under resulting in more restricted sea level rise, while crossing will result in many metres. And sea level rise is likely to continue unabated if thresholds are crossed. It’s critical that we identify the thresholds and act on emissions accordingly.”
Read more: On thin ice: Melting of the doomsday glacier in Antarctica could raise sea levels by 65 centimetres
Dr Felicity McCormack, senior lecturer at Monash University, and investigator with the Australian Research Council’s Special Research Initiative Securing Antarctica’s Environmental Future, also spoke with Cosmos quoting globally renowned Australian climate scientist Professor Will Steffen who died last month, aged 75.
“As Will Steffen put it, every fraction of a degree of avoided warming matters. There’s no acceptable level of warming – the warming that we’ve already seen is already having unacceptable impacts on human, species and ecosystem survival.”
“With advances in technologies for measuring and modelling Antarctica and Greenland, we are getting more confident in how these ice sheets will respond to climate change,” McCormack adds. “But the essential message remains the same: we must do all we can to limit further warming and we must do it now.”
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