I believe what you are trying to say is "Golly gee! Temperatures have been rising pretty fast in the past twenty years or so, compared to the past hundred years in which we have been capable of measuring global temperatures".
Yes, there are ice core measurements, etc but those generally point to mixed conclusions that are somewhat inconvenient for proponents of anthropogenic global warming (for example, it was far warmer during the Holocene Maximum in most of the world, and even the Medieval Warm Period featured warmer climate in most of Europe). "But wait!" you say, "Temperature increases of the time were not constant throughout the world so they don't count!", to which I reply "True, but such increases don't apply now, either. For example, I recall it being noted a while back that large portions of the USA aren't warming at all, and are, in fact, beginning to cool down significantly. This indicates that if humans are affecting the climate at all with emissions, the effects are marginal at best."
True, it might not be solar emissions causing an increase in temperature (though again, these increases are definitely not worldwide at this point, so it isn't even honest to claim that "the earth is warming" at all), but then we aren't exactly far ahead in terms of our ability to understand the climate in a massive way. Personally, I would imagine that what warming there is is being caused by water vapor and ocean currents, which would certainly make some sense. But then, we don't know enough to be able to make strong, accurate predictions either way. There was once a time where the most groundbreaking, revolutionary and accurate belief was that the earth was actually round (true) and that the sun rotated around it (false). This wasn't because the earth was really flat (which was the alternative of the time), but because ancient astronomers were effectively incapable of figuring it out with the instruments at hand. Likewise, our climate models are crude and far off target with predictions. It is a bit silly to claim that we have suddenly understood the mysteries of the climate in their entirety when we obviously haven't.
This is still a pointless argument, though. Assuming there is no global warming, we have nothing to worry about. Assuming there is (and assuming that nothing natural counterbalances the excess of CO2, like how some consider that plants may thrive from the CO2 and absorb more, producing more oxygen and growing faster), we have a very long time before most of the negative effects become prominent (don't give me the Al Gore "flooding Florida" garbage, the most alarmist of AGW supporting scientists predict far milder effects in the worse case scenario over a far longer period of time) by which time we will probably have a more efficient energy source due to a decrease in supply and increase in demand of fuel. However, assuming you are right (and libertarianism is flexible enough to handle the situation even in the worst case scenario), here is a list of things things a libertarian society would do (most of which even apply to lukewarm, beltway libertarians, though I will mention if they don't):
-No more energy subsidies. No truly libertarian society would subsidize oil companies (though a somewhat libertarian society might, but we are talking about one willing to at least go to minarchy along the lines of a Ron-Paul-Sets-All-The-Rules world if not farther), and thus oil would lose a lot of its competitiveness in the market. This would result in far less incentive to use oil, resulting in other energy sources becoming commercially viable without subsidies. Mind, alternative energy would lose subsidies too, but frankly if it can't stand without subsidies it is definitely a poor alternative (the prime example of this is the hybrid car, which requires more energy to make its engine than it saves through efficiency). Ultimately, improvements in technology would result in a superior, probably cleaner form of energy.
-Without government controlled energy grids, a lot of burning electricity plants would be far too inefficient to make a profit (especially without subsidies), while some alternative energy sources might become far more popular due to increased utility (for example, wind turbines and solar panels would be far more prevalent, though their inefficiencies would have to be dealt with to be made viable outside of a handful of areas).
-The road system would probably stop receiving subsidies. Roads would still be present, but they would likely be owned by either landowners (the roads would be auctioned off to those homesteading the land nearby or abandoned altogether depending on the circumstances) or by road companies. The road owners wouldn't want to have to use their own money to pay for "frequent drivers", and thus would charge a fee for driving on them. Competition would keep costs below what they are now (paid in taxes), but those who drove everywhere for no good reason would begin to feel the cost hurting their pocketbook. Meanwhile, those who only drove when necessary would note that the loss of many taxes otherwise used to pay for infrastructure (varies depending on the country, but in my own it is the gas tax) would result in them actually benefiting from their decision, which coincidentally is the "environmentally friendly" one as well. Alternative modes of transportation would become far more viable without subsidized roads, too.
-A minor one, but this would still probably have an effect. The military, no longer needing to go on foreign adventures, would be greatly downsized (if not privatized altogether). They would cease to consume as many resources as when they are maintaining over a hundred bases across the world and fighting many wars, and thus would greatly decrease their emissions.
