With climate hazards set to uproot millions of vulnerable families and send them flocking to cities for refuge, mayors worldwide are demanding action to strengthen urban resilience—and to limit global warming to 1.5°C.

The intensity of climate migration will increase with rising temperatures, finds a new report by C40 Cities. By 2050, up to eight million people could migrate to just 10 cities identified in the study, all of them in the Global South. “That’s on top of economic and political refugees, and migrants from other countries,” writes Bloomberg News.

While most climate migrants head to cities, conversations around climate migration have focused on national-level impacts, says C40. That leaves a “critical gap” in the understanding of how cities are affected.

C40 used data from 10 cities in Bangladesh, Brazil, Colombia, Ghana, Jordan, Pakistan, and Sierra Leone to see how climate hazards like flooding, drought, low crop yields, and sea-level rise will influence migration.

In Bangladesh, capital city Dhaka, which already has 12 million residents, could receive 3.1 million internal migrants by 2050 due to severe flooding. In Colombia, nearly 600,000 displaced people are expected to settle in Bogotá, which already struggles with water shortages.

These vulnerable migrants often trade one set of climate risks for another, says C40. In cities, they may be crowded into informal settlements, facing deadly heatwaves, devastating landslides, and dangerous levels of air pollution.

Vital Role for Cities

But C40 says cities “are not just passive recipients of climate migrants; they are active players in shaping the outcomes.” To successfully accommodate newcomers, leaders must adopt inclusive policies that address the needs of migrants while enhancing urban wellbeing for all. Cities can also “leverage green transition opportunities” to provide accessible, decent, green jobs for all.

Locally-led, proactive interventions will be key to managing rapid urbanization, preventing sprawl, and reducing pressure on municipal services, C40 adds. But cities will need more financial support to adapt to the challenges.

“Only 8% of the US$5 trillion required annually for urban climate action is available,” C40 Cities Co-Chair Yvonne Aki Sawyerr, Mayor of Freetown, Sierra Leone, said in a release.

Paris Targets Keep Millions at Home

C40 urges international cooperation to rein in emissions and slow the increase in climate migration. The report says cities must do their part to reduce fossil fuel dependence—but adds that national governments too must “follow the lead of many cities” and meet the International Energy Agency’s call to halve global fossil fuel use by 2035.

Limiting warming to 1.5°C will help keep millions of potential migrants safe at home, C40 says. Three times fewer internally displaced people will struggle to put down stakes in Bogotá, Rio de Janeiro, and Karachi if the Paris agreement’s goals are met.

“The biggest issue we need to address to reduce the impacts of climate migration on cities is to reduce emissions,” Jazmin Burgess, director for inclusive climate action at C40, told Bloomberg. “And that responsibility doesn’t sit exclusively with cities. It demands action from everyone.”