Of the over 400 climate scenarios assessed in the 1.5°C report by the Intergovernmental Panel on Climate Change (IPCC), only around 50 scenarios avoid significantly overshooting 1.5°C. Of those only around 20 make realistic assumptions on mitigation options, for instance the rate and scale of carbon removal from the atmosphere or extent of tree planting, a new study shows. All 20 scenarios need to pull at least one mitigation lever at 'challenging' rather than 'reasonable' levels, according to the analysis. Hence the world faces a high degree of risk of overstepping the 1.5°C limit. The realistic window for meeting the 1.5°C target is very rapidly closing.