Don't breed. The carbon cost of children is through the roof.
Occasionally one will see headlines claiming a gigantic carbon cost to having kids. Because your kids use carbon, and their kids will use carbon, and their kids, and so on forever. The problem with this is that carbon usage is not constant with time. The amount of renewable energy generated is rising exponentially, and ways of using this energy like electric cars are becoming widespread. In not too many decades the world will become carbon-neutral, just because that is more economically efficient. So your kids and their kids will not actually emit large amounts of carbon, and the carbon cost of having kids is actually relatively small.
This does not imply that climate change is not a problem - we are still capable of emitting dangerous amounts of carbon before the switch to renewables - but it does mean that having kids is not actually an overwhelming cause of carbon emissions.
(Not to mention that our kids are just as human as we are, and if we deserve to live despite our carbon emissions, so do they. The world will survive no matter what they do, climate change is a problem because it's a problem for people, but you don't solve a problem for people by getting rid of the people)