Moroni Remuyna’s home in the Brazilian town of Ferreira Gomes, on the banks of the Araguari river, was submerged in 17 feet of water when an upriver dam was built. Operators failed to notify the town. “The history of dam-building has been one of incompetence, greed, illegality and callousness,” says Remuyna.

Despite this history, it can sound like today’s debate around hydropower is settled: many people think it is unquestionably the clean energy solution—renewable, scalable and storable. At the World Hydropower Conference in May, it seemed that development and environmental organizations were united in support of this vision and previous opponents of dams began touting their benefits. The United Nations Green Climate Fund recently committed $136 million to fund two dams. One is in the Solomon Islands, a nation highly vulnerable to climate change.

But this conversation has to dig deeper: into what a hydropower project will mean for the communities up and downstream of a dam, and into whether hydropower dams are really as climate-friendly as people like to think. At the launch of the massive World Commission on Dams (WCD) Report in 2000, Nelson Mandela said:

“The overall performance and impacts of dams presents us with a more complex and often bleak picture, especially for the unspoken minority, and for nature.”

The environmental and socioeconomic impacts of dams often mean that they simply aren’t worth building, and a series of studies over the past twenty years has built a strong argument that dams actually contribute to climate change. Given the severity of dams’ impacts, locally and on the climate, our search for climate and development solutions needs to involve the voices of communities who will be most affected by these projects. We all stand to benefit immensely from their knowledge.

The Climate Change Calculus

We need clean energy in order to kick our addiction to fossil fuels. This is about human rights and standing with the world’s frontline communities, not only future generations and polar bears. A series of studies going back to 2000 shows that dams aren’t that clean. There’s evidence that four percent of the total warming caused by humans can be attributed to the world’s 52,000 large dams, and that these dams account for more human-caused methane emissions than any other single source.

It happens like this: first, plants are uprooted when the dam reservoir is initially created. This biomass releases carbon as it rots. Second, it decomposes on the bottom of the reservoir, without oxygen, causing a buildup of methane in the water. Finally, when this water is released, the trapped methane is put directly into the air. While this sounds like a single source of greenhouse gases, quickly exhausted, seasonal changes in reservoir depth cultivate a new supply of decaying plant matter every year. This cycle effectively traps carbon-dioxide, in the form of plant life around the reservoir, and turns it into methane to be shot into the atmosphere.

According to a 2007 study by the Brazilian Institute of Space Research (INPE), large dams emit 104 million metric tonnes of methane every year. That’s almost a quarter of human-caused methane emissions. A 2013 follow-up by German researchers looked at small dams that trap water less than 50 feet deep and showed that their methane emissions account for a 7 percent increase in global freshwater greenhouse gas emissions. In total, dams account for more GHG emissions than the country of Canada.

The evidence is strong enough that 170 organizations released a statement at the 2015 UN Climate Change Conference in Paris declaring that large hydropower projects are not viable climate change solutions.

A Changing Climate Means Changing Renewables

Regardless of dams’ role in global warming, a shifting climate will change how sustainable hydropower really is. Untapped hydropower resources in developing countries get a lot of attention. Laos, for example, currently has plans to build 70 dams, 11 on the mainstream of the Mekong River, and has already borrowed over twice its GDP for infrastructure. But water resources are vulnerable to climate change in ways that we don’t yet fully understand. During the El Niño in 2015-16, the Kariba Dam on the Zambezi River was forced to decrease power production by 50 percent. According to a 2017 World Bank report on energy and water resources in Sub-Saharan Africa, “Climate change is expected to reduce rainfall levels, increase rainfall variability, and increase ambient temperature.” That dam in the Solomon Islands isn’t looking so sustainable anymore.

The Experts We’ve Ignored: The Communities Who Call These Rivers Home

Despite all of this uncertainty, the path forward is pretty clear: It’s vital that we listen to the communities who know these rivers. Environmental and social impact assessments (EIAs and SEIAs) aren’t just a procedural box to be checked, but a chance to consult with the experts.

The Mekong River Basin, for example, is home to 65 million people. Two-thirds of them rely on subsistence fisheries for their food. By 2030, there could be over 80 dam projects on the Mekong and its tributaries. A report by the Mekong River Commission shows that these projects will cause inequality and poverty to rise for twenty-five years after their construction. The businesses involved will receive most of the benefits, as governments in the region lack programs to distribute the socioeconomic gains among people living in the area. In the case of the Xayaburi dam in Laos, the World Bank and the Asian Development Bank refused to back the project because of the environmental and social risks. Thai banks later moved in to fund the project.

The people who will be most affected by dams have been fighting to tell the world what’s at stake. In the Amazon River Basin, over 400 dams have been proposed. For the Chadin 2 dam, on the Marañón River in Peru, most of the 200 issues raised in the EIA remain unresolved. Local communities maintain an organized resistance to the project, and one leader in this fight, Mr. Hitler Rojas Gonzales, has been killed.

We Know What Happens When We Don’t Listen

Thayer Scudder has seen the impact of dams on local communities for 58 years—he built a career consulting on large dam projects. The New York Times calls him “the world’s leading authority on the impact of dams on poor people.” In 1956, Scudder worked on the construction of the Kariba Dam, located between Zambia and Zimbabwe. The Kariba Dam holds back the world’s largest human-made reservoir and was funded by the largest loan ever made by the World Bank at the time. It displaced 57,000 indigenous Tonga people and 86 workers died during construction. Scudder has worked on many similar projects since. He now says that large dams simply aren’t worth it and that many of those being constructed today “will have disastrous environmental and socio-economic consequences.”

Scudder’s last project was the Nam Theun 2 Dam in Laos. Its creditors were required to implement programs to increase the quality of life of displaced populations. The dam was finished in 2010 but these programs were never effectively implemented.

“The [Lao] government wants to build 60 dams over the next 20 or 30 years, and at the moment it doesn’t have the capacity to deal with environmental and social impacts for any single one of them,” said Scudder in an interview.

We’ve also forgotten what we’ve learned from listening to the communities impacted by dams. The WCD, led by the World Bank, concluded back in 2000 that, though dams may drive development,

“in too many cases an unacceptable and often unnecessary price had been paid… by people displaced, by communities downstream, by taxpayers and by the natural environment.”

The WCD commissioned 130 technical papers and reviewed 1,000 dam projects. Their report showed that dams rarely deliver on developers’ promises of electricity and irrigation. It recommended that creditors refuse to support a project until there is a guarantee of

“prior consent of those affected, proper compensation schemes and environmental safeguards.”

But even when corporations and governments ignore all the evidence that hydropower is not a shoe-in clean energy solution, dams still may not look like a good option.

The Cost of All That Concrete

In terms of pure economics, a 2014 Oxford University study strongly supports Scudder’s conclusion that the math doesn’t work. The study looked at 245 large dams built between 1934 and 2007 and found that “the actual construction costs of large dams are too high to yield a positive return.” The costs of inflation and currency depreciation place a big financial burden on the developing countries who choose to construct these dams. Domestic companies sell the electricity in local currencies but massive loans must still be paid off in dollars. The WCD report also points out that dam projects often funnel money from aid agencies and international financial institutions to foreign construction companies. Hydropower megaprojects fueled debt crises in Turkey, Brazil, Mexico and former Yugoslavia. The 2014 Oxford study looks at the Diamer-Bhasha Dam on the Indus River in Pakistan, still under construction. Originally slated to cost $12.7 billion, in 2008 dollars, and be completed by 2021, evidence now shows that it may not be finished until 2027. By that point, the dam may cost $35 billion, one-quarter of Pakistan’s GDP—and that’s without accounting for inflation. These lessons from history make Laos’ 70-dam hydropower blitz, and its towering cost, even more hair-raising.

Inclusive Development Isn’t Just Jargon

“The debate about the role of dams and development is thus moving beyond emotional arguments to real science,” claimed an article last month in EconoTimes, referring to the new emerging consensus among select financial and environmental groups to endorse dams. But we don’t get to pick between emotion and science. When communities see their livelihoods threatened—to the tune of $13 billion in the case of fisheries on the Lower Mekong—they have a right to get emotional. The same is true for Moroni Remuyna’s hometown in Brazil.

Similarly, we don’t get to select which areas of science we consider and which we ignore. Studies demonstrating how dams contribute to global warming have now gained traction in political spheres and we can push for policies that account for these impacts.

Rather than endorsing or rejecting hydropower dams, as a blanket principle, we’re obligated to remain open to what the experts are telling us and to fight with communities who see the impacts of dams every day—to include them in developing climate solutions and fostering economic equality.