The world has already far surpassed limits on global warming. In 2016 the CO2 levels in Earth's atmosphere passed the symbolic 400 parts per million threshold, making extremely unlikely pollution in the atmosphere will drop below those levels again in our lifetime. According to the researchers, it's no longer enough to reduce emission levels, we now need to take steps to physically remove carbon dioxide from the atmosphere -- by around 12.5 percent.

This could be done with low-cost agricultural measures such as planting trees. Other steps, such as carbon-capture and the development of 'carbon-sucking' infrastructure, are more expensive but could become necessary if action isn't taken soon. The paper estimates such processes could cost up to $535 trillion this century and notes that: "Continued high fossil fuel emissions unarguably sentences young people to either a massive, implausible clean-up or growing deleterious climate impacts or both."