Fig. 2

Tradeoffs between hydropower generation and carbon intensity for portfolios of proposed Amazon dams. In a–d, each point represents a portfolio of dams. The optimal dam portfolios for each value of installed capacity (Pareto frontier) are shown in dark blue, and randomly generated suboptimal dam portfolios are shown by gray symbols. a and b show carbon intensity outcomes considering only the 351 proposed dams over 20-year and 100-year time horizons, whereas c and d show outcomes starting from the existing set of 158 Amazon dams (blue square; current installed capacity = 33 GW for an emission of 213 kg CO₂eq MWh⁻¹ over a 20-year horizon and 87 kg CO₂eq MWh⁻¹ over a 100-year horizon). The ranges of carbon intensities of coal- and natural gas-fired power plants reported by the IPCC are shown in the purple and orange bands, respectively⁷. The carbon intensity of electricity produced from natural gas is closer to that of coal over shorter time frames due to its higher methane emissions. The green dashed line indicates the projected carbon intensity of the global electricity sector based on a scenario consistent with the UN 2030 Agenda for Sustainable Development²³. A suboptimal and a Pareto-optimal dam portfolio, both with the same installed capacity (15 GW) but with contrasting carbon intensities (100-year time horizon), are illustrated in (e) and (f)