The U.N. Intergovernmental Panel on Climate Change has issued its gravest warning yet, saying major, irreversible climate catastrophe is unavoidable and that the world has a narrowing window to make drastic changes to prevent even greater devastation. That’s according to the IPCC’s first climate assessment in eight years, which shows the world is on track to surpass an average temperature rise of 1.5 degrees Celsius above preindustrial levels, failing to meet the goals of the Paris Climate Agreement. Even if the goal is met, the world will still have to contend with fast-melting Arctic ice, sea level rise and the warming and acidification of oceans — all of which contribute to more extreme weather events, including droughts, floods, wildfires and deadly heat waves. The IPCC does not offer recommendations to governments, but the U.N. says countries need to immediately move away from fossil fuels and to stop adding carbon to the atmosphere by 2050 in order to slow or halt the most catastrophic outcomes.