What Would Cities Look Like With 3 Degrees C of Warming vs. 1.5 Degrees?

What Would Cities Look Like With 3 Degrees C of Warming vs. 1.5 Degrees?

The world has already experienced a 13-month streak of record-breaking global temperatures, and 2024 is on track to be the hottest year on record. Global average temperatures are now perilously close to exceeding 1.5 degrees Celsius (2.7 degrees Fahrenheit) above pre-industrial levels, a threshold scientists warn will bring increasingly dangerous droughts, wildfires, and other climate change impacts.

Researchers project nearly 3 degrees Celsius (5.4 degrees Fahrenheit) of temperature rise by 2100 without significant action to reduce greenhouse gas emissions. That means almost 600 million people will be exposed to flooding from rising seas, food production will drop by as much as half, and habitats will suffer disastrous levels of loss. But what will these two temperature scenarios – 3 degrees Celsius versus 1.5 degrees Celsius – look like in specific cities around the world?

The Difference Between 3°C and 1.5°C of Warming is Sizable for Cities

New data from the World Resources Institute (WRI) finds that in most cities, the difference between 3 degrees Celsius and 1.5 degrees Celsius of warming is substantial. WRI analyzed potential climate hazards for nearly 1,000 of the world’s largest cities – currently home to 2.1 billion people, or 26% of the global population.

At 3 degrees Celsius of warming, many cities could face month-long heat waves, skyrocketing energy demand for air conditioning, and a shifting risk for insect-borne diseases – sometimes simultaneously. People in low-income cities are likely to be the hardest hit. These findings hold immense consequences for people’s lives and livelihoods, as well as for cities’ economies, infrastructure, and public health systems.

This is especially important as cities are home to 4.4 billion people globally – more than half the world’s population – and will grow rapidly over the next two decades. By 2050, as another 2.5 billion people move to urban areas, two-thirds of humanity will live in cities, with over 90% of that growth in Africa and Asia.

Longer, More Frequent Heat Waves

At 3 degrees Celsius of warming, most cities can expect both longer and more frequent heat waves than at 1.5 degrees Celsius. For example, the average duration of the longest heat wave in a year may jump from 16.3 days at 1.5°C to 24.5 days at 3°C, with over 16% of the world’s largest cities – home to 302 million people – exposed to at least one heat wave lasting a month or longer every year.

Heat wave frequency may also increase, from an average of 4.9 per year at 1.5°C to 6.4 per year at 3°C, with an increasing number of cities facing double-digit heat waves annually. This can take a massive toll on public health, especially for vulnerable groups like the elderly and children. Poorer neighborhoods within cities will feel the effects more acutely, as they often have fewer green spaces to cool the air and less access to air conditioning.

Soaring Cooling Demand

Longer, more frequent heat waves and extremely hot days will significantly raise the demand for cooling in homes and workplaces – and with it, the demand for energy if those needs are met through mechanical means like air conditioning. At 1.5 degrees Celsius of warming, approximately 8.7 million people across a handful of cities could face double their historical cooling demand. At 3 degrees Celsius, that number rises to 194 million people.

This has huge implications for energy infrastructure and access, especially in regions where power relies on fossil fuels. Many places that haven’t needed cooling strategies before – like northern Europe or the U.S. Pacific Northwest – will have to develop them, while cities that are already hot, like Tehran and Marrakech, will see their cooling demand increase even faster.

The urban poor, who often live in more densely populated and hotter parts of cities with poor-quality buildings and limited access to cooling, will be disproportionately affected. Only about 8% of the 2.8 billion people living in the world’s hottest and often poorest regions currently have air conditioning in their homes.

Shifting Disease Patterns

Warmer conditions often fuel the spread of mosquito-borne diseases. Comparing 1.5 degrees Celsius and 3 degrees Celsius of warming, the average city may experience 6 more days per year with optimal temperatures for arbovirus transmission, such as dengue, Zika, and chikungunya. Low-income cities will be particularly hard hit, potentially seeing 87 peak arbovirus days per year at 3°C, compared to just 32 days for high-income cities.

The incidence of malaria, on the other hand, is expected to decrease globally as temperatures in many places become warmer than optimal for malaria-transmitting mosquitoes. However, cities in more temperate regions like Europe and North America could see their malaria risks increase, as the disease creeps into areas where it hasn’t been seen in living memory.

Compounding Risks for the Most Vulnerable

Climate hazards rarely come in isolation, and low-income cities will suffer compounding risks from the interacting effects of extreme heat and disease, potentially straining already-insufficient health care systems, infrastructure, and budgets.

Sub-Saharan Africa is likely to be the hardest-hit region, with cities facing the largest estimated increases in heat wave frequency, peak arbovirus days, and energy demand for cooling at 3 degrees Celsius of warming compared to 1.5 degrees Celsius. Latin American and Indonesian cities also face some of the highest compounding risks.

These findings underscore the need for urgent action. National and local governments must work to make their cities more climate-resilient through measures like improving early warning systems, boosting health care capacity, and investing in passive cooling solutions. At the same time, the world must redouble efforts to slash greenhouse gas emissions and limit global temperature rise to 1.5 degrees Celsius, the target set in the Paris Agreement. The difference between these two warming scenarios could be a matter of life or death for billions of people.

To learn more about Europe’s shift to clean energy, visit the European Future Energy Forum.

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