On July 12, 2017 Seth Wynes and Kimberly A Nicholas published:

The climate mitigation gap: education and government recommendations miss the most effective individual actions

http://iopscience.iop.org/article/10.1088/1748-9326/aa7541

Of course, having one less offspring is the best way of reducing CO2 by a factor of 1000 or more. 

Wynes found that swapping out your lightbulbs would reduce CO2 emissions by less than .2 tons per year. Living car free, however? That reduces your CO2 emissions by more than 3 tons. Having one less child reduces climate change impacts by 120 tons of CO2 emissions per year, in part because it’s not only a reduction of the emissions associated with the child, but also means avoiding emissions that their child would have created.

 More significantly, a US family who chooses to have one fewer child would provide the same level of emissions reductions as 684 teenagers who choose to adopt comprehensive recycling for the rest of their lives.