Global warming is an ongoing phenomenon wherein the average temperature of the atmosphere of Earth is rising dramatically because people burned a lot of fossil fuels (i.e. oil made out of long-dead animals). Some effects of global warming are: the melting of arctic sea ice, the increasing prevalence of large-scale weather-related disasters, rising sea levels, and climatic shifts that will permanently change the arability of recently farmable land.
As the rising seas swallow coastal cities, increasingly frequent hurricanes and typhoons wreck tropical settlements more and more often, and world governments refuse to act with any amount of alacrity, almost every single climate science alive increasingly agrees that global warming will most likely kill and at minimum substantially inconvenience most people.
Unless we figure out how to remove substantial amounts of carbon from the atmosphere and bury it underground, which is unlikely, the best idea we really have at the moment is to plant more trees. Meanwhile, the Amazon rainforest is literally on fire.
Global warming is the most dangerous.
