30 july 2020

Extra 23 million people could face coastal flooding within 30 years, even with emission cuts, study says

* Human-caused sea level rise, storm surges and high tides will put trillions of dollars of assets at risk around the world by the end of the century
* Even with relatively ambitious emission cuts, millions more people around the world will experience coastal flooding within the next 30 years, a study has found.

Graham Readfearn, The Guardian, July 30, 2020

The combined impacts of human-caused sea level rise, storm surges and high tides could expose an extra 23 million people to coastal flooding within the next 30 years, even with relatively ambitious cuts to greenhouse gas emissions, a new global study has found.

In a worst-case scenario where emissions continue to rise and no efforts are made to adapt to the rising sea levels, coastal assets worth US$14.2tn – about 20% of global GDP – could be at risk by the end of the century.

Rising sea levels caused by global heating that expands the oceans and melts land-based ice could mean that one-in-100-year floods occurring now would become one-in-10-year floods by the end of the century. As much as 4% of the world’s population could be affected by flooding.

The study, published in the journal Scientific Reports, identified “hotspot” regions at risk of extensive flooding.

South-eastern China, Australia’s north, Bangladesh, West Bengal and Gujarat in India were especially at risk. In the United States, North Carolina, Virginia and Maryland were considered to be most exposed, as were the UK, northern France and northern Germany.

But the study also shows how the risk of damage from rising sea levels and storm surges will continue to rise even if emissions are kept to a level that would keep the global temperature rise to well below 2C by the end of this century.

The new study builds on findings published by the United Nations Intergovernmental Panel on Climate Change in 2019 that predicted extreme sea level events could be near annual occurrences by the middle of this century on many coastlines.

Prof Ian Young, a co-author of the study at the University of Melbourne, said: “We certainly need to mitigate our greenhouse gases but that won’t solve this problem.

“The sea level rise is already baked in – even if we reduce emissions today the sea level will continue to rise because the glaciers will continue to melt for hundreds of years.”

According to the study, about 148 million people globally are exposed to flooding events today.

If greenhouse gas emissions rise moderately – the equivalent of 1.8C of global warming by the end of the century – a further 54 million people will be exposed. But if emissions are allowed to spiral in a worst-case scenario, then this number rises to 77 million.

About US$10.2tn of coastal assets are exposed to coastal flooding in 2100, even with emissions kept at moderate level, according to the study.

All the figures modelled in the study assume that no adaptive measures are taken, illustrating the benefits of taking early action to reduce the impact of flooding events.

Young said: “When most people think of sea level rise they think about 3 or 4mm per year, but when flooding occurs it happens it’s when you also have a storm.

“That happens today and we have seen that on the coast of New South Wales last week. Sea level rise exacerbates the magnitude – and increases the frequency – of these flooding events.

‘There are significantly larger areas of land flooded and that will have significant economic impacts on infrastructure.

“Even if we mitigate greenhouse gases it does not make much effect. We have to adapt to this – it is going to happen so we have to look at either hard engineering solutions, or do we look at planned retreat and move populations and that’s incredibly difficult, or there are nature-based coastal defence systems.”

Ebru Kirezci, the lead researcher, also of the University of Melbourne, said: “We need to adapt to sea level rise and climate change.

“Adaptation is the only way out and we need to adopt some risk mitigation strategies like sea walls and dykes and develop forecasting and warning systems, or coastal retreat, which means the relocation of coastal communities to safer places.”

Prof John Church, a leading expert on sea level rise at the Climate Change Research Centre at the University of New South Wales, who was not involved in the study, said the findings were valuable.

He said the study had brought together several elements to estimate extreme impacts, but there was more work to be done to understand additional impacts from changes to the severity of storms and waves.

He said there was also likely to be significant impacts along estuaries and it was important to note that “sea level rise will not stop in 2100 under any scenario”.

He said: “With more emissions the higher the [sea level] rises, with commitments of metres of sea level rise over coming centuries with the higher scenarios. The impacts to 2100 are the introduction to the future.”

While coastal flooding could impact 20% of global GDP this, he said, was a reflection of a society that “love the coast”.

“We need more thoughtful and forward-looking planning.”

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