It would cost $39 billion USD per year to provide universal education in low- and lower-middle-income countries.
That’s less than the USA increased their defence spending in 2018. Or to look at it another way it’s 6% of the $639 billion defence budget. Or, slightly more than the total USD officially contributed to global development in 2016.
Combined with improving Family Planning, universal education would have the most significant effect on global carbon generation of any single action.
The most significant effect. More than wind farms. Or electric cars. Or even eating a more plant-based diet (which incidentally is the most significant thing an individual has control over and can change immediately).
*Please take ten minutes to browse drawdown.org. I’ve never seen such a comprehensive and well presented set of information on climate change.