From Miami to Shanghai: 3C of warming will leave world cities below sea level

An increased level of climate change would lock in sea-level rises that can not be reversed. This will affect hundreds of millions of people, Guardian data analysis shows.

Hundreds of millions of people living in cities around the world face their cities being submerged by rising sea waters. The latest UN warning says that the world is on course for 3C of global warming, according to a Guardian data analysis.

Data from the Climate Central group of scientists  shows that 3C of global warming would lock in irreversible sea-level rises of perhaps two metres. Cities from Shanghai to Alexandria, and Rio to Osaka will be the worst affected. Miami would be under water – as would the entire bottom third of the US state of Florida.

The Guardian has found that local preparations for a 3C world are as little as international efforts to prevent it from happening. At six of the coastal regions most likely to be affected, government planners have done very little to deal with the problem – and in some cases have done nothing.

This comes ahead of the latest round of climate talks in Bonn next week. Negotiators will work on ways to monitor, fund and increase national commitments to cut CO2 so that temperatures can rise on a safer path of between 1.5 and 2C. This is the goal of the Paris agreement reached in 2015.

The momentum for change is currently too slow, according to the UN Environment Programme. In its annual emissions gap report, released on Tuesday, the international body said government commitments were only a third of what was needed. Non-state actors such as cities, companies and citizens can only partly fill this void, which leaves warming on course to rise to 3C or beyond by the end of this century, the report said.

The UN’s environment chief, Erik Solheim, said progress in the year since the Paris agreement has been inadequate. “We are not doing nearly enough to save hundreds of millions of people from a miserable future,” he said.

Nature’s ability to help may also be diminishing. On Monday, the World Meteorological Organisation said concentrations of carbon dioxide in the atmosphere rose last year at a record speed to reach 403.3 parts per million. This level has not seen since the Pliocene era three to five million years ago.

A 3C rise would lead to longer droughts, fiercer hurricanes and lock in sea-level rises. Depending on the speed at which icecaps and glaciers melt, this could take decades or more than a century. Colin Summerhayes of the Scott Polar Research Institute in Cambridge said three-degrees of warming would melt ice much further and faster than currently expected. This may potentially raise sea levels by two metres by 2100.

At least 275 million people live in vulnerable areas. The majority of them in Asian coastal megacities and industrial hubs such as Shanghai, Shenzhen, Bangkok and Tokyo.

Japan’s second biggest city, Osaka, is projected to lose its business and entertainments districts of Umeda and Namba unless global emissions are forced down or flood defenses are built up. Officials are slowly accepting they must now put more effort into the latter.

“In the past our response was focused on reducing the causes of global warming, but given that climate change is inevitable, according to the Intergovernmental Panel on Climate Change (IPCC), we are now discussing how to respond to the natural disasters that will follow,” said Toshikazu Nakaaki of the Osaka municipal government’s environment bureau.

In Miami, there is a sense of urgency at city hall. Commissioners are asking voters to approve a “Miami Forever” bond in the November ballot. This includes $192m for upgrading pump stations, expanding drainage systems, elevating roads and building dykes.

Elsewhere, there is less money for adaptation and a weaker sense of urgency. In Rio de Janeiro, a 3C rise would flood famous beaches such as Copacabana, the waterfront domestic airport, and many of the sites for last year’s Olympics. But the cash-strapped city has been slow to prepare. 

In Egypt, even a 0.5m sea-level rise is predicted to submerge beaches in Alexandria and displace 8 million people on the Nile Delta unless protective measures are taken, according to the IPCC. But local activists say the authorities see it as a distant problem. “As far as I’m concerned, this issue isn’t on the list of government priorities,” said Ahmed Hassan, of the Save Alexandria Initiative.

The impacts will also be felt on the economy and food production. Among the most vulnerable areas in the UK is Lincolnshire, where large areas of agricultural land are likely to be lost to the sea.

“We’re aware that climate change is happening faster than expected so we are trying to mitigate and adapt to protect people and property. We can’t stop it, but we can reduce the risk.” said Alison Baptiste, director of strategy and investment at the UK Environment Agency. She said the measures in place should protect most communities in the near and medium term, but 50 years from now the situation will become more challenging. “If climate change projections are accurate, we’re going to have to make some difficult decisions.”

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