Hope it won't be unwelcome for me to toss a small elaboration on Klein's points about capitalism in here:

We must understand and explain which problems capitalism can and cannot solve. Capitalism can accelerate the development of more efficient solar, wind, hydro, etc. power (though this ability is tied to the price of the cheapest fossil fuel, and the relative abundance of coal means this ability will be quite limited for a long time) and battery and transmission efficiency. It may even be able to clean up certain continents and regions while polluting other continents and regions all the more heavily. However:

(a) It cannot solve the problem of reaching real sustainability*. It will always incentivize kicking the can down the road. This is because producing a product in a truly sustainable way is more expensive than producing it in a way that has an invisible-to-the-consumer environmental cost (such as using up a finite resource). Since, all things being equal, cheaper products that do the same thing will sell better, those who take the unsustainable route will undercut anyone trying to make things sustainably, drive them out of business, and take over their market share. The outcome will be a market full of actors none of whom will make truly sustainable products.

(* You know, actually being able to do it on an ongoing basis FOREVER. That is what the word “sustainable” should actually mean.)

(b) It cannot solve truly global problems like global warming and ocean acidification. The logic of competition-for-profit means that one company/country/region will always be incentivized to pollute to gain an advantage over its rivals (or just avoid being outcompeted and eaten by them). All actors on every scale are incentivized to cheat as long as their existence and well-being is endangered by others possibly cheating more than them. It is worthless for a world full of capitalist countries, each with its own capitalist bloc that must compete with all others, to sign a legal agreement to try to solve this problem. As long as competition-for-profit continues to play any role at all in large-scale economic activity, that legal agreement must inevitably be disobeyed by all actors.

(c) Only in a global political-economic system that is actually being run according to a single, unified plan (at least ecologically speaking) where literally everyone’s material standard of living is both guaranteed and tightly tied to everyone else’s can these problems be solved. If all would-be “cheaters” had to share the “profit” gained from contributing to global pollution with literally the rest of the people on the globe, there would be so little personal advantage to be gained from polluting extra as to not make it worth it.

In this vein, it is very much worth noting that

Cuba is a world leader in ecologically sustainable practices. It is the only country to have begun the large-scale transition from conventional farming, which is heavily dependent on fossil fuels, to a new agricultural paradigm known as low-input sustainable agriculture. (source)