Cities Will Suffer Health and Infrastructure Crisis Under 3° C vs. 1.5° C Warming, With Low-income Cities Worst Impacted

With over two-thirds of the world's population expected to live in cities by 2050, new global data on the 1,000 largest cities provides a granular view into potential climate futures - highlighting growing hazards and the urgent need for climate adaptation investment

WASHINGTON (September 19, 2024) - Under the world's current trajectory of 3 degrees C (5.4 degrees F) of warming from pre-industrial averages, cities across the globe may endure far more frequent and longer heat waves, skyrocketing demand for cooling, and more widespread disease risk, compared to 1.5 degrees C (2.7 degrees F), according to new analysis from World Resources Institute's (WRI) Ross Center for Sustainable Cities. Low-income cities and cities in sub-Saharan Africa, Latin America and Southeast Asia are likely to be hardest hit.

WRI analyzed climate hazards for 996 of the world's largest cities - home to 2.1 billion people (26% of the global population) - using estimates based on downscaled global climate models. The modeling and analysis show a sizable difference between 1.5 degrees C and 3 degrees C for urban areas, underscoring the need for city and national governments to inform their investments and policies with city-level data. This new statistical modeling method can make it easier to predict city-scale impacts from global data and points to the urgency for even more granular modeling work to enable cities to prepare for the worst effects of climate change and rally to reduce emissions faster. This work was supported by Bloomberg Philanthropies.

"The difference between 1.5 degrees C and 3 degrees C has life or death consequences for billions of people worldwide," said Rogier van den Berg, Global Director, WRI Ross Center for Sustainable Cities. "This data should serve as a wakeup call to every city and national government leader: now is the time to start preparing cities for a much hotter world, while doing everything we can to slash emissions."

At 3 degrees C, most cities can expect both longer and more frequent heat waves compared to 1.5 degrees C, with impacts on public health, labor capacity and productivity. In a 1.5 degrees C world, the longest heat wave each year may last an average of 16.3 days, with 3% of the world's largest cities experiencing heat waves lasting one month or longer annually. However, under 3 degrees C of warming, the average duration of the longest heat wave could jump to 24.5 days, with more than 16% of cities - home to 302 million people today - exposed to at least one heat wave lasting a month or longer every year.

Heat waves may also become more frequent. At 1.5 degrees C of temperature rise, the average city may experience 4.9 heat waves per year. At 3 degrees C of warming, the number rises to 6.4 heat waves per year, with an increasing number of cities facing heat waves in the double digits.

Grappling with extreme heat will significantly raise the demand for cooling - and consequently, for energy. At 1.5 degrees C, about 8.7 million people across a handful of cities could face a 100% increase in their cooling demand (compared to 1995-2014 averages). With 3 degrees C of warming, that number rises to 194 million people in cities potentially seeing their cooling demand double from historic levels. That has huge implications for energy infrastructure and access.

In terms of the spread of disease, higher temperatures create more optimal environments for mosquitos that carry arboviruses, such as dengue, Zika, West Nile, yellow fever and chikungunya in new places. Comparing 1.5 degrees C and 3 degrees C of warming, the world's largest cities could see on average 6 more days of peak arbovirus-transmission days every year. But results vary considerably by location. Brazil is already experiencing a dengue crisis, and at 3 degrees C of warming, 11 of its largest cities could see high arbovirus risk for at least six months of the year.

For malaria, the rise in global temperatures from 1.5 degrees C to 3 degrees C may reduce the number of peak malaria days globally from an average of 114 to 104.4 days in cities, as temperatures become warmer than what is optimal for malaria-transmitting mosquitos. But cities in more temperate regions like Europe and North America could also see their malaria risks increase.

These findings bear immense consequences for people's lives, cities' economies, and infrastructure and public health systems. This is especially important as cities are home to more than half the world's population - 4.4 billion people - and are expected to grow rapidly over the next two decades. By 2050, two-thirds of the global population will live in cities, with another 2.5 billion people moving to urban areas. Over 90% of urban growth will be in lower-income countries in Africa and Asia.

"Climate change has profoundly unequal impacts both across cities and within cities," said Anjali Mahendra, Director of Global Research, WRI Ross Center. "Cities in low-income countries are often more afflicted and have fewer resources to cope, which means we need to drastically increase financing for adaptation and find ways to direct it to the hardest hit cities and communities. Even within a well-resourced city, the most vulnerable populations will be disproportionately affected."

Sub-Saharan African cities may endure multiple severe climate impacts, potentially simultaneously. Comparing impacts at 1.5 degrees C vs. 3 degrees C of warming, the region ranks first on average for the largest estimated increase in heat wave frequency (up 56%, to 6.5 occurrences per year) and peak arbovirus days (25 additional days, totaling 129 annually). It also sees the third largest estimated increase in duration of heat waves (up 58%, to 20 days) and the second biggest estimated increase in energy demand for cooling (an additional 208 cooling degree days).

Latin American cities rank second on average for the greatest estimated increase in heat wave frequency (up 48%, to 7.5 occurrences annually) and have the second-highest estimated increase in the number of days optimal for arboviruses at 3 degrees C (13 additional days, to 91 days annually) compared to 1.5 degrees C.

In Southeast Asia, Indonesian cities face some of the highest compounding risks from both hotter temperatures and greater disease. Three of the four cities in the world with the greatest estimated increase in peak arbovirus days from 1.5 degrees C to 3 degrees C of warming are in Indonesia: Yogyakarta (273 day increase), Jember (151 day increase) and Padang (148 day increase).

"Better data is the key to sound decision-making, especially during this era of accelerating climate impacts and urgent need for make-or-break action," said Eric Mackres, Senior Manager, Data and Tools, WRI Ross Center. "It is our hope that city leaders will use these hazard projections to inform decisions and investments that will protect residents against the climate impacts they will face if we fail to change our current emissions path."

The new research builds on analysis released at the COP28 Local Climate Action Summit, hosted by Bloomberg Philanthropies and the COP28 Presidency with support from WRI. The Summit marked a historic moment to formally recognize the pivotal role city and other local leaders play in climate action. The Summit produced the Coalition for High Ambition Multi-level Partnerships, an initiative endorsed by over 70 national governments to drive a new approach to updating Nationally Determined Contributions by harvesting the best ideas for climate action from the local level, with the goal of ensuring the next round of national climate targets are as ambitious and inclusive as possible.

"This research makes it clear that we can't afford to delay action on climate change any longer as dire consequences await cities in a 3 degrees C world," said Antha Williams, who leads the Bloomberg Philanthropies' Environment program. "For over a decade, we've helped support mayors' forward thinking and bold leadership in the fight against climate change. Now it's more important than ever for national and local governments to come together to accelerate progress and protect the millions of lives in urban communities from the threatening impacts of climate change."

National and local governments must work urgently to improve collaboration, increase financing for adaptation, double down on policies to reduce greenhouse gas emissions, and use a data-driven approach to prioritize the most likely and urgent risks.

About World Resources Institute
WRI is a trusted partner for change. Using research-based approaches, we work globally and in focus countries to meet people's essential needs; to protect and restore nature; and to stabilize the climate and build resilient communities. We aim to fundamentally transform the way the world produces and uses food and energy and designs its cities to create a better future for all. Founded in 1982, WRI has nearly 2,000 staff around the world, with country offices in Brazil, China, Colombia, India, Indonesia, Mexico and the United States and regional offices in Africa and Europe. Learn more at WRI.org and on X @WorldResources.

About WRI Ross Center for Sustainable Cities

WRI Ross Center for Sustainable Cities is World Resources Institute's program dedicated to shaping a future where cities work better for everyone. It enables more connected, compact and coordinated cities. The Center expands the transport and urban development expertise of the EMBARQ network to catalyze innovative solutions in other sectors, including air quality, water, buildings, land use and energy. It combines the research excellence of WRI with two decades of on-the-ground impact through a network of more than 370 experts working from Brazil, China, Colombia, Ethiopia, India, Mexico, Turkey and the United States to make cities around the world better places to live. More information at www.wrirosscities.org.

About Bloomberg Philanthropies

Bloomberg Philanthropies invests in 700 cities and 150 countries around the world to ensure better, longer lives for the greatest number of people. The organization focuses on creating lasting change in five key areas: the Arts, Education, Environment, Government Innovation, and Public Health. Bloomberg Philanthropies encompasses all of Michael R. Bloomberg's giving, including his foundation, corporate, and personal philanthropy as well as Bloomberg Associates, a philanthropic consultancy that advises cities around the world. In 2023, Bloomberg Philanthropies distributed $3 billion. For more information, please visit bloomberg.org, sign up for our
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