In Balbina, a small town in the heart of the Brazilian Amazon, the shoreline of a vast reservoir sparkles blue and a mild wind ruffles the water, lifting small whitecaps. Within a few months, fire will devastate vaste swathes of the forest, some not far from here, but the story I've come to investigate lies just below the water's surface, where millions of trees have been drowned by a hydroelectric dam blocking the Uatumã river. The submerged jungle is no longer sucking carbon dioxide out of the atmosphere. Instead, the rotting corpses of once-magnificent trees are belching out yet more greenhouse gases.
No wonder the Balbina dam is known by experts as "the worst hydroelectric power plant in the world". And yet its environmental impact is worse than previously thought, as I discovered when I visited the region earlier this year to spend time with climate researchers. Their findings suggest that any dam built in tropical lowlands could be exacerbating the climate crisis, which is particularly alarming now that Brazil's president Jair Bolsonaro has promised to extract more of the Amazon's resources, including hydroelectric power.
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