Two degrees Celsius
Due in large part to this enhanced greenhouse effect, the world today is nearly 1˚C (1.8˚F) warmer than it was before the Industrial Revolution. While 1˚C may seem hardly noticeable on a sunny day, countries are already seeing the severe effects of planet-wide warming at this level. Heat waves are lasting longer, crop yields are shrinking, and rising sea levels are threatening coastal areas.
Scientists warn that, without a significant reduction in greenhouse gas emissions, human activity will continue to raise global temperatures to 2˚C (3.6˚F) above nineteenth-century averages. Should this happen, the results would be catastrophic. And, in some cases—such as species going extinct, coral reefs dying, and sea levels rising—the effects would be irreversible.