Carbon dioxide levels just hit 415 ppm for the first time in some three million years.  Humans have never lived on this or any planet with CO2 levels that high.

According to the U.N. Advisory on Greenhouse Gasses, temperature increases beyond one degree Celsius may cause rapid, unpredictable and non-linear responses to the climate that could lead to extensive ecosystem damage.

Two degrees of temperature increase exponentially increases the likelihood of ice-free summers, and the Head of the Polar Oceans Physics Group says the blue ocean event frequency and timeline have been grossly underestimated.

Anyone who tells you how or when we experience the effects of 415 ppm is either speculating or lying.  But we've written some pretty big checks and there's no reason to believe that Mother Nature's not going to cash them, and probably soon.

The Earth will be fine, ultimately.  It's we human beings that have reason to worry.

It's been a good run H. sapiens.  Hope evolution comes up with a more intelligent lifeform on the next iteration.