Except that some of the absolute worst ecological tragedies in the modern world were done in socialist systems

The Dust Bowl. Exxon Valdez. Deepwater Horizon.

You're suggesting heavy regulation of social and economic systems which is the entire point of socialism. You say socialism doesn't work, but that is exactly what you're describing.

And capitalism does not want to exist in a society of international regulation. Those concepts are at odds with one another.

If you like markets you might be more interested in learning about democratic market socialist countries and how they operate. The Nordics lean in that direction - after all, social democracy spawned out of orthodox marxism. The core idea in OG Nordic economics is simple: more democracy. You don't need a min. wage, let unions bargain for their salaries, which is why McDonalds famously pays such a massive min. wage in Denmark. Fund and support democratically owned housing (housing coops, of which 20% of Norway resides in and still growing vs pop. growth despite no more gov. funding) or democratically run grocery stores (Finland has the highest density of consumer coops in the world) - housing coops usually have democratically agreed policies like not being able to treat your property like a commodity/investment by primarily renting it out (thus not contributing as much to rising housing prices), and consumer coops have been at the forefront of more environmentally and labour friendly behaviour. All the Nordics have worker board representation - workers make up a percentage of the board and help steer the company. There's also the social wealth funds in Norway that give the government the power to guide corporations towards more ethical behaviour by owning significant amounts of shares in businesses, both domestically and internationally - although some argue Norway could learn from the Alaska SWF which pays its citizens dividends from the SWF. All of this builds towards economic democracy, or more commonly known as "socialism", but in a way that has had great success. They've reeled some of those things back in recent decades, and the negative effects are clear to see - Norway stopping its funding of housing coops has meant a growing housing crisis much like the rest of Europe (with few exceptions, like Vienna (Austria) and Finland where socialised housing plays a bigger role).

It is absolutely not our growth as a population that has affected climate change. That's capitalist doomer propaganda. Those actually responsible for it are the few at the top of capitalist hierarchies. Politicians, billionaires, oil and coal barons. Right now we van feed up to 11 billion people, yet there is still mass starvation and poverty. Capitalists require poverty so that people are desperate enough to work the shitty jobs the capitalists "create".

As for the rest of what you said, I briefly touched upon this, but even CCP and USSR admitt(ed) they weren't really communist, and whether they're socialist is extremely debatable. They're not communist because by their own admission they're preparing for a communist world, but they keep saying that and it never comes about. These regimes lie constantly, but even if they lied rarely I'd still not believe they want actual communism because it'd involve giving up their power. What these states actually are is state capitalist.

They're communist in the same way the Nazis were socialist, or the DPRK is a democratic republic: they're not.

That'd just it, there's nothing as efficient as it current system. There are plenty of options that are less efficient and better for the environment/people but nothing that's as efficient in terms of resource allocations.