Here’s an inconvenient truth: We’ve polluted the atmosphere with so many gigatons of greenhouse gases that just slashing emissions — which we still absolutely have to do — will no longer be enough to avert the worst impacts of climate change. We’ll need to also actively remove greenhouse gases from the atmosphere. The United Nations’ Intergovernmental Panel on Climate Change estimates that by 2050, even assuming steep emission cuts in the next few decades (and emissions have been rising, not falling), we’ll need to take out something like 5 to 10 gigatons of CO2-equivalent each year.

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