See this report from an outpost of the climate change millennial movement.

Rumors abound that the militaries and intelligence services of a variety of great power countries have, in the past, worked on dubious approaches to weather control. The idea of a geoengineering arms race may superficially parallel this line of thinking, but it's actually a very different concept. Unlike "weather warfare," geoengineering would be more subtle and long-term, and would have nothing to do with steering hurricanes or inducing local droughts; moreover, unlike weather control, we know it can work, since we've been unintentionally changing the climate for decades.

Geoengineering as a military strategy would appear to offer a variety of benefits. Research can be done out in the open, taking advantage of civilian work on anti-global warming geoengineering ideas. If my argument that nuclear weapons and open-source warfare have made conventional warfare essentially obsolete is correct, climate-based warfare would offer an alternative non-nuclear weapon, one that would be out of the reach of non-state actors. And the more we learn about how human activities alter the climate -- in order to alter those activities -- the more options might open up for intentionally harmful manipulation. . .

some nations may believe that they can deal with global warming better than their competitors, or even benefit from it -- that, in the words of Vladimir Putin, it "wouldn't be so bad." Putin may have been joking, but a number of Russian scientists presenting at the 2003 World Climate Change Conference in Moscow seemed to make the same argument. Moreover, as this recent article in El Pais documents (English summary here, Google translation here), Russia's doing nothing to reduce its carbon emissions, and is instead building more coal-fired power plants; the only reason that it's in compliance with the Kyoto treaty is that its economy has declined relative to 1990. Given Putin's hardline propensities, if he thought that Russia would be harmed less than its competitors (or even benefit), would he be willing to reject the idea of taking advantage of that situation? . . .

In this scenario, even passive resistance to action against global warming could be seen as a mode of terraforming warfare.

How realistic is this idea? It depends. Given the high likelihood of further research into geoengineering projects for purely anti-global warming reasons, it seems almost certain to me that military or government officials in more than one country will come to similar conclusions about the technology's potential as a weapon. Actual weaponization of geoengineering methods would (one hopes) be slowed or stopped as more information comes in about unanticipated results of geoengineering tests, cost and/or efficiency, and the irrationality of believing that variations in the impact of climate disruption would be enough to alter balances of power.

One hopes. But it's hard to go wrong by assuming that someone in power is going to want to take advantage of a new way of "winning," no matter how difficult or irrational.

Welcome to the era of the Earth itself as a weapon.

I have no doubt that geoengineering sciences will progress. It's an old idea in SF that has been fictionally applied to other planets as well as earth. It isn't fundamentally different from draining swamps or irrigating deserts, and in that sense is an ancient tool in the human kit.

The bizarre bit in the above millennial rant is the idea that "passive resistance to action against global warming could be seen as a mode of terraforming warfare". What action? Isn't that the real issue? Even many of those who find the speculative notions of AGW compelling resist the current crop of actions proposed by activists since they would have trivial effects on AGW while having large effects on human societies. Those socio-economic effects are seen as the true objective, and AGW as an excuse to oppress society, leaving it even more vulnerable to AGW. In that scenario it is the activists, rather than the resistance, who are engaging in terraforming warfare.