Who is 'they' here? Certainly there was a one-child policy. I don't think it could be said that the consequence of female abortion and infanticide was the intention (or even an expected consequence) of the policy.
It seems that many people in the comments are set on demonizing the country. For this I think better points to raise are the ethnic cleansing of the Uyghur 'reeducation' program, or the usurping of peaceful autonomous neighbors like Tibet and Hong Kong (maybe Taiwan later). But none of this has anything to do with obligations around CO2 emissions, which they are addressing more than any country on the planet, as I've commented elsewhere:
