I used to be a member of the Green Party in the UK. In my experience, the people involved in Green politics are more likely to be "romantics" than "realists". Hardly anyone in the Green party in the UK is prepared to look at things objectively from a scientific or economic viewpoint - it's an ideology. A lot of Greens are also into Anarchism, Socialism, Feminism, New Age mysticism (crystals etc.), Veganism and that kind of thing. They are viscerally anti-science and anti-business - cartoons in the Green Party magazine always depicted male scientists and businessmen as being responsible for all the world's problems. And there really are political groups in Western countries advocating a "back to nature" philosophy - if you don't believe me walk into any radical bookstore that sells amateur left-wing political magazines.
I don't want to start a flame war here, so I'd better make it clear I am NOT saying that I personally don't believe there is a scientific case for environmentalism. Actually, I believe the degredation of the environment is a much greater threat to the world than Al Qaida. I just want to make a point about the type of people who become politically active environmentalists.
The modern Green movement started in the 1960s after the publication of Rachel Carson's "Silent Spring" (1962) and I think it ran out of popular support in the 1990s. I think a good POD for a more environmentalist world would be to have the US launch a pre-emptive war on the USSR prior to the USSR developing the atomic bomb (this was seriously considered at the time). This leads to a capitalist Russia, Eastern Europe, China and South East Asia. By the 1980s Russia and Eastern Europe have a standard of living equivalent to that of Europe, and China and South-East Asia have a standard of living equivalent to that of Taiwan or South Korea. This would mean vastly more international trade and investment than in OTL, making the whole world much richer. Environmental problems such as pollution, ozone depletion, global warming, deforestation, resource depletion etc. would occur more rapidly and on a larger scale than in OTL. Suppose mainstream political parties are slow to react to public concern about the environment with anything other than soothing words, after all they have business interests to keep happy. That would leave the way clear for a Green party to win an election. The party has a charismatic leader who is also a canny politician - he presents his party as more moderate than it really is. When in power he doesn't bother about legal niceties such as property rights or elections - we have an IMMEDIATE ENVIRONMENTAL CRISIS here and the end (saving the planet) easily justifies any temporary measures. Probably the leader's ultimate ideal is a kind of primitive communism anyway. When I was in the Green Party their manifesto held "News from Nowhere" by William Morris (1891) to be the kind of society they were working towards.
Incidentally "News from Nowhere" is a very cool book - it's a Victorian time-travel story in which an average joe wakes up 150 years in the future (he takes a while to figure out what happened to him) to discover that England has become a kind of medieval communist utopia. It's more readable than "Brave New World".
I have quite a few books by "realist" environmentalists that discuss how the coming environmental catastrophe is nearly upon us and the kind of new political order needed to cope with the realities of our living in a world of limited resources (all of these were published in the early 1990s). Some of them are written from a "right-wing" economic-liberal social-authoritarian viewpoint and some of them from a "left-wing" economic-authoritarian social-liberal viewpoint but there are two things all of them are in agreement upon - we need a much stronger world government and we need enforced population control.
Oh, and you might find this amusing - the UK Green Party doesn't have a leader - it has two "principal spokespersons" (one male and one female, natch), who stand for one year - but have no influence on party policy (party policy is a totally democratic process in which every member can participate - which leads to a VERY long, detailed and eccentric manifesto). A UK Green government would not be totalitarian (disbanding the army being one of their objectives - if an enemy invades the population is to engage in Ghandi-style passive resistance) but it would be . . . interesting.