If that's even the case, it's mostly because the most efficient economic system is, in the long term, going to be the economic system that generates the most economic activity and hence the most externalities.
Climate change in particular was only discovered in the second half of the 20th century, while the root cause (the burning of fossil fuel hydrocarbons) was done inside developed economies of all stripes since at least the 18th century. The other environmental problems caused by 18th, 19th, and early 20th century industrialization have largely been addressed over time as they've been discovered, particularly in capitalist economies. In fact, the most popular proposals for addressing climate change are market-based controls on carbon emissions (either cap-and-trade or carbon taxing), which in other contexts have proven very effective. One of the best qualities of capitalism is the way that it can be applied to such ends via simple policies that merely apply incentives and use the mechanisms of the market rather than directly dictating command-and-control over economic activity.
Incidentally, another environmental catastrophe of communism was the disappearance of the Aral Sea, which was once larger than all but one of the Great Lakes. The Soviets started to intentionally redirect the sources of the Aral Sea into irrigation megaprojects in the 1960's and ended up destroying the entire ecosystem, in exchange for growing cotton in Uzbekistan.
You can also count Chernobyl, the Darvaza gas crater and I'm sure there are other idiotic soviet mistakes. They did not care much about people let alone the environment. Just look at China, another communist country.
Climate change in particular was only discovered in the second half of the 20th century, while the root cause (the burning of fossil fuel hydrocarbons) was done inside developed economies of all stripes since at least the 18th century. The other environmental problems caused by 18th, 19th, and early 20th century industrialization have largely been addressed over time as they've been discovered, particularly in capitalist economies. In fact, the most popular proposals for addressing climate change are market-based controls on carbon emissions (either cap-and-trade or carbon taxing), which in other contexts have proven very effective. One of the best qualities of capitalism is the way that it can be applied to such ends via simple policies that merely apply incentives and use the mechanisms of the market rather than directly dictating command-and-control over economic activity.
Incidentally, another environmental catastrophe of communism was the disappearance of the Aral Sea, which was once larger than all but one of the Great Lakes. The Soviets started to intentionally redirect the sources of the Aral Sea into irrigation megaprojects in the 1960's and ended up destroying the entire ecosystem, in exchange for growing cotton in Uzbekistan.