All coastal cities are vulnerable to climate change. For thousands of years, coastal living was preferred, owing to the abundance of food supplies, ease of transportation, and potential for defending against adversaries. Today, at least 10 percent of the world’s population lives in a low-lying coastal areas. But what was once an asset is increasingly a liability. The rapid expansion of coastal cities has eroded natural barriers, destroyed resources, and degraded water quality. As a result, swelling coastal communities are exposing ever-greater numbers of people to hurricanes, storms, floods, landslides, and sea level rise.
Some coastal cities are more at risk from sea level rise and other climate-related threats than others. Within the next few decades, over 570 low-lying coastal cities could face at least 0.5 meters, over 1.6 feet, of sea level rise. If this scenario comes true, it could put over 800 million people at risk and exact some $1 trillion in total economic cost. While Asian and African cities are especially exposed, one of the most vulnerable cities in Latin America is Rio de Janeiro. Climate scientists and the city’s own planners believe the city’s built environment is at risk of sea level rise, flooding, increased precipitation, and heat islands making large parts of it virtually uninhabitable.
One reason why coastal cities are so exposed to climate-related threats is a combination of bad planning and rapid urbanization. Rising water levels and the increasing frequency and severity of floods and extreme heat are only part of the problem. Another is that many coastal cities are built directly on top of coastal plains, often near estuaries and lagoons. People, including the poorest residents, are often forced to live on precarious land holdings, including drained wetlands and marshes—or directly in the lagoons as in the slums of Lagos, Nigeria. This exposes them to not only flooding but also compaction, resulting in sinking infrastructure. The areas most susceptible to climate stress are often those registering the highest population density and housing populations at the lowest rung of the income ladder.
Rio de Janeiro’s present climate vulnerability is partly a legacy of its historically chaotic and unequal urban development. After ceding the title of national capital to Brasília in 1960, Rio began to sprawl uncontrollably. Within five decades, the metro area’s population tripled. Population growth exacerbated the shortage of affordable housing and contributed to the steady expansion of unplanned and improvised neighborhoods westward and northward. Informal settlements, or favelas, proliferated alongside waterways and on hillsides.
Today, Rio de Janeiro numbers an estimated 6.7 million people. It is the country’s second-largest city by the size of its economy, but ranks only 327th in terms of GDP per capita, 71st in municipal competitiveness, and among the most unequal not just in Brazil, but in the world. Rio is also notoriously violent: Over 2,400 people were murdered in the metropolitan area in 2020, not including approximately 1,000 people reportedly killed by police. What is more, an estimated 60 percent of the city is controlled by militias, while drug trafficking factions oversee dozens of poorer neighborhoods.
Against this backdrop, it is no surprise that the city is struggling to mitigate and adapt to natural disasters and climate change. A combination of turbo-urbanization and disorganized urban planning contributed to a rapid depletion of natural forest cover. Instead of climate-proofing the city with often cheaper nature-based solutions such as reforesting and wetland restoration, state and metropolitan authorities have funneled funds into cement, brick, and steel. The reduction of tree cover, erosion of coastal areas, and explosion of concrete have contributed to increase average temperatures there by 0.05 degrees Celsius per year.
Global average temperatures are expected to increase by 2 degrees Celsius by 2050 in a “business as usual” scenario. Warming in Rio de Janeiro is expected to lead to longer, more severe, more frequent, and more lethal heat waves, affecting especially the elderly and poorer populations. Rising temperatures could also lead to a 0.3 to 2.15-meter rise in sea levels by 2100, potentially inundating much of Rio de Janeiro’s surface area, including residential and commercial real estate, public parks, ports, and power grids.
There are already signs of what’s to come. The state of Rio de Janeiro has recorded hundreds of natural disasters since the early 2000s; today, researchers estimate that at least 155,000 people living in over 1,300 high risk areas are vulnerable to landslides and floods. One of the most devastating, a massive storm and series of landslides in 2011, killed over 800 people, left 30,000 homeless, and exposed tens of thousands more to water-borne disease such as leptospirosis. The World Bank estimated the costs of the tragedy at over $2 billion. Yet in the decade since the disaster, too little has been invested in rebuilding depleted infrastructure, much less climate-proofing it. In 2012, the city started building four underground reservoirs and a diversion tunnel to improve the control of mild-to-medium floods, but these are inadequate to counter the looming threats.
Climate change threatens to not only impose tremendous humanitarian costs on Rio de Janeiro but also disrupt its key sources of income. The state and city are highly dependent on oil revenues. When oil prices tanked between 2014 and 2016, the state declared a financial “calamity” shortly before the hosting the Summer Olympics. By 2020, revenues from oil and gas royalties continued to slump. Given global divestment from hydrocarbon industries, future economic planning will require alternative sources of revenue.
The other key source of revenue for Rio de Janeiro is tourism. Yet rising seas and temperatures, alongside violence, threaten its value proposition. Today, Rio ranks behind other Brazilian cities such as São Paulo, Belo Horizonte, and Porto Alegre when it comes to attracting tourist dollars. Brazil as a whole has slipped to 32nd place behind Belgium and Denmark. Yet there is tremendous potential for Rio’s tourist industry to grow if only more emphasis were placed on nature-based solutions that can help resolve some of its climate insecurities.
The first step to building climate resilience involves identifying climate threats and developing strategies to mitigate and adapt to them. Yet there are few up-to-date scientific studies documenting the scope, scale, and consequences of climate change in Rio de Janeiro. There are few publicly available studies on sea level rise, coastal erosion, or heat islands for most Brazilian cities. And yet over 60 percent of Brazil’s population live in low-elevation coastal cities: Belém, Florianópolis, Fortaleza, Paranaguá, Salvador, Recife, and Vitória are especially at risk.
One Brazilian city that has started taking action to adapt to climate change is Santos, home to Latin America’s busiest seaport. Santos processes over a hundred millions tons of cargo a year; the equivalent of around 27 percent of Brazil’s trade balance passes through the port. After documenting persistent sea level rise, the city authorities introduced tax deductions for investment in alternative energy and promoted green roofs, reforestation, natural barriers, drainage channels, and pumping stations.
Curitiba is another Brazilian city that is globally recognized for climate action innovation. In the 1980s, the city launched a bold strategy to protect green areas, promote recycling, and invest in waste management. Its “green exchange” program swaps recycled items for food. The city’s ratio of around 600 square feet of green space per inhabitant is around four times that of São Paulo and well above the international standard. Today, Curitiba is just one of two cities in Brazil with a climate adaptation plan, earning it the designation of the most sustainable city in Latin America.
These kinds of innovative solutions could help redress many of Rio de Janeiro’s competing crises of climate vulnerability, insecurity, inequality, and economic decline. Expanding green spaces, cooling heat islands, curbing pollution, and improving affordable housing can all help decrease inequality, reduce violence, and increase economic opportunity. The alternative of coastal erosion, increased flooding, and searing heat risks making parts of Rio de Janeiro uninhabitable, exacerbating crises in a cash-strapped city.
Brazilian cities can bolster their defenses against climate change by forming updated plans that emphasize adaptation and mitigation and are built on the basis of genuine public consultation. Most major cities have established some kind of council to at least discuss climate action. Yet many Brazilian cities are lagging behind: 11 of the country’s 27 state capitals have outdated master plans exceeding the 10-year mandatory renewal. To date, only a handful of Brazilian cities are actually tracking greenhouse gas emissions. Only Belo Horizonte, Curitiba, São Paulo, and Rio de Janeiro have designed adaptation or mitigation strategies.
Coastal cities such as Rio de Janeiro need to experiment with different strategies to strengthen climate resilience. There are plenty of ideas out there—including sponge-cities that deploy a combination of repurposed built space, rain gardens, ponds, and wetlands to store excess water, and ambitious eco-restoration projects, such as favela green roofs and green corridors. Nature-based solutions are not just an add-on; they are key to the city’s survival and an on-ramp to sustainable economic renewal.