If we just abide by current national commitments under the Paris Agreement to reduce emissions, researchers have estimated we could have a 50% chance of experiencing warming greater than 3.5 ºC, and a 10% chance of experiencing warming greater than 4.7 ºC, by 2100 (relative to 1850-1900 temperatures). Especially at the higher end of this range, there will likely be very significant humanitarian harms, including food and water shortages, large scale displacement of vulnerable populations, and decreased global stability.
There is also a non-negligible chance that we could see larger increases in global temperatures, especially if we do not cut emissions in line with current commitments, in which case harms could be much worse. Especially in the more extreme scenarios, a warming climate may increase the risk of human extinction or civilizational collapse.
Promising options for working on this problem include research into the likely outcomes of higher levels of carbon emissions and strategies for mitigating the worst effects. One can also advocate for strategies to reduce emissions (such as carbon taxes or encouraging low emissions technologies) through careers in politics, think-tanks or journalism, or work as an engineer or scientist to develop technologies that can reduce emissions or their impact.