And the CO2 is only a portion of the picture.   Yes, a great deal of CO2 was pumped into the atmosphere previously during the Permian extinction, and that was due to nature.   We have now done the same, more CO2 than has been in the atmosphere for hundreds of thousands of years.   But we haven't merely pumped catastrophic amounts of CO2 into the atmosphere, we've also deforested a great deal of the planet and damaged remaining forests with encroachments, we have eradicated wildlife, sealife, fisheries, arable land; we've dumped tons of radioactive waste into the environment and much of it is leaking, and we have around 440 active nuclear power plants that all need constant energy and half a century to shut down; we've polluted the oceans beyond description with giant gyres of plastic and dead zones and sewage and agricultural runoff, and so on. 

This is not going to end well, and it's later than most people think.