Billions of people in big cities around the world face increasing climate-related risks, from heat waves to energy shortages. Here, a street scene in Dhaka, the capital of Bangladesh. Credit: Kevin Krajick/Earth Institute

Billions of people in thousands of cities around the world will soon be at risk from climate-related heat waves, droughts, flooding, food shortages and energy blackouts by mid-century, but many cities are already taking action to blunt such effects, says a new report from a consortium of international organizations.

The report, called The Future We Don't Want, estimates that by 2050,

1.6 billion people living in more than 970 cities will be regularly exposed to extreme high temperatures.

Over 800 million living in 570 cities will be vulnerable to sea-level rise and coastal flooding.

650 million, in over 500 cities, will be at risk of water shortages.

2.5 billion people will be living in over 1,600 cities where national food supplies will be threatened.

The power supply to 470 million people, in over 230 cities, will be vulnerable to sea-level rise.

215 million poor urban residents living in slum areas in over 490 cities will face disproportionate climate risks.

The report was assembled by C40 Cities, a group of big cities working to face climate change; the Global Covenant of Mayors for Climate & Energy, which has signatories in thousands of cities representing some 700 million people; the Urban Climate Change Research Network (UCCRN), a global consortium of institutions and experts based at Columbia University's Earth Institute; and the UK-based consultant group Acclimatise. It was presented this week at the Adaptation Futures conference in Cape Town, South Africa, where representatives of cities around the world are sharing ideas on how to become more resilient to changing climate.

"For decades, scientists have been warning of the risks that climate change will pose. Now we have the clearest possible evidence of just what these impacts will mean for [the] world's cities," said Mark Watts, executive director of C40 Cities. "Our research should serve as a wake-up call."

The report features steps that major urban areas already taking to adapt. Cynthia Rosenzweig, co-chair of the UCCRN and head of the climate impacts group at Columbia's Center for Climate Systems Research, said that if such efforts are scaled up and widely adopted, they would stem some of the worst effects.

Some of the efforts covered by the report include:

To battle extreme heat, Seoul has planted 16 million trees and expanded its green space by 3 square kilometers. The city has also set up shaded cooling centers for those unable to access air conditioning.

New York City is improving coastal flood mapping, strengthening large-scale coastal defenses and building smaller, strategically placed local storm surge barriers around the city.

São Paulo has set up reward schemes to encourage citizens to use less water, while investing in the city's pipeline system to reduce water leakage.

Paris plans to establish more than 80 acres of urban agriculture within the city's boundaries by 2020. By 2050, 25 percent of the city's food supply will be produced in the metropolitan region.

London is improving drainage to ensure that key infrastructure can withstand heavy flooding, The city is also encouraging decentralized energy supplies to reduce the risk of widespread blackouts if any one power source is damaged.

Lima has created a poverty map of the city to help policy makers focus resources on the most vulnerable and under-served areas, where people are most exposed to extreme heat.

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Provided by Earth Institute, Columbia University

This story is republished courtesy of Earth Institute, Columbia University http://blogs.ei.columbia.edu.