The buildup of greenhouse gases will take hundreds (link) to possibly hundreds of thousands of years (link) to breakdown and return the atmosphere to levels that we have been used to during our years on earth as human civilizations. The climate changes are also likely to affect the oceans for hundreds of thousands of years. (link) The graph of the increase in the main greenhouse gases is fairly level and then exponentially increases in the recent past: The Big Picture Breakdown of Greenhouse Gases.
Another brief article discussing a previous major change in climate which caused a mass extinction of species at the time:
And an additional post on this site: Climate change, ocean currents, and an ice age.
This is serious.
Disclaimer: Opinions are my own and the information is provided for educational purposes within the guidelines of fair use.