City Solution: Hunting Dengue in Rio de Janeiro, Brazil
Arboviruses are of particularly urgent concern in Latin America. 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. Rio de Janeiro may see significantly more illness if global warming reaches 3 degrees C, as the expected number of peak arbovirus days increases by 71%, from 69 to 118 days per year.
As temperatures in Rio de Janeiro become more hospitable to dengue-carrying mosquitos, the city is investing in improving the availability of dengue vaccines and controlling the mosquitos themselves. Community health workers crisscross the city, hunting for places where standing water accumulates and mosquitos can breed. And Rio de Janeiro is using another disease — Wolbachia, a bacterium that infects insects — to inhibit dengue transmission in infected mosquitos. Rio de Janeiro and five other Brazilian cities release Wolbachia-infected mosquitos by the tens of thousands. These mosquitos behave no differently from uninfected mosquitos, but they harbor less dengue virus and infect other mosquitos. A similar Wolbachia program in Yogyakarta, Indonesia resulted in a 77% reduction of dengue incidence.
Low-income Cities Will Face Compounding Climate Risks
Climate hazards rarely come in isolation. Low-income cities, in particular, will suffer compounding risks from the interacting effects of above-average increases in temperatures and disease, potentially straining health care systems, infrastructure and budgets that are already insufficient to meet residents’ needs.
Sub-Saharan Africa is likely to be the hardest hit region for several indicators at 3 degrees C of global warming. The region’s cities may endure multiple severe climate impacts, potentially simultaneously. Comparing impacts at 1.5 degrees C versus 3 degrees C of warming, the region’s cities rank first on average for the greatest estimated increase in heat wave frequency (up 56%, to 6.5 occurrences per year) and peak arbovirus days (25 additional days, totaling 129 annually). They also see the third-largest estimated increase in the annual longest heat wave duration (up 58%, to 20 days) and the second-biggest estimated increase in energy demand for cooling (an additional 208 cooling degree days).
Although Africa is only responsible for 2%-3% of the world’s greenhouse gas emissions, many of its sub-Saharan cities are most affected by climate change-induced hazards. At 3 degrees C of warming, cities like Freetown, Sierra Leone and Dakar, Senegal could endure heat waves lasting longer than a month, with an average of seven heat waves in a year, demanding greater energy for cooling (13% and 20% above historical reference period averages, respectively). Many cities in the region are already dealing with rapid population growth, conflict and unregulated development. These compounding climate hazards only add to the region’s vulnerability.
Latin American cities rank second on average for the greatest estimated increase in heat wave frequency (up 48%, to 7.5 occurrences annually). The region’s cities 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.
Cities in Indonesia face some of the highest compounding risks of 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).
Reaching 3 Degrees C Is Not a Foregone Conclusion
The future under 3 degrees C of warming looks dire, but these data are only an estimate of effects for one pathway. We have a choice about our climate future. The technology already exists; with the right political will, we can mitigate the worst of these effects.
National and local governments must work urgently to make their cities more climate-resilient while slashing emissions. Specific priorities include:
- Double down on policies to reduce greenhouse gas emissions: Climate problems will only worsen until the world brings greenhouse gas emissions down to net zero. National governments must implement policies aligned with the international Paris Agreement on climate change; cities can set targets and adopt policies to contribute to meeting these goals.
- Increase finance for climate adaptation: Many low-income cities have climate adaptation plans, but implementation lags due to lack of funding. Adaptation needs for low-income countries are $387 billion per year — 10-18 times bigger than current international public adaptation finance flows.
- Invest in resilient infrastructure: Adaptation solutions like cooling infrastructure, early-warning systems and heat action plans protect people’s health and boost cities’ long-term resilience. Nature-based solutions like urban forests and wetlands also do these things while bringing the added benefits of nature to city residents.
- Improve collaboration between cities and national governments, and across city departments: Multi-level partnerships and coordination are key to tackling greenhouse gas emissions and implementing resilience at the scale required to save and improve people’s lives. While in many parts of the world different levels of government tend to operate in silos, using separate strategies, some national governments see the value of cities and support them as climate-solution allies. More than 70 countries committed at the 2023 UN climate summit (COP28) to collaborate with cities on their next national climate plans, due in early 2025, through the CHAMP Initiative. Others should follow.
- Take a data-driven approach: Climate-hazard forecasts for cities can help them focus on the most likely and urgent climate risks while informing targeted investments and policies. City-scale, city-relevant data like ours should be at the center of planning and budgeting for climate adaptation and resilience.