Climate change means that many farm animals will have two breeding seasons, good news for lovers of lamb and mint producers.
From Jules and James Blogspot
Even if one assumes the premise that we are "optimally adapted" to the present climate (which I think would be difficult to rationally defend), it does not follow that changes to the climate would result in net costs.
In fact, our adaptation to the current climate (eg in agriculture and infrastructure, as have been mentioned) is also a matter of economics, technology and politics, and we can guarantee that these will continue to change at quite a rate.
Of course we can all agree that a drought in an area that is already somewhat short of water is a bad thing that will likely cost money, compared to exactly the same situation without the extra drought. However, an increase in rainfall in such an area is likely to be beneficial (so long as it is not excessive and leads to flooding), even if society is well adapted to the status quo. The opening of the Northwest Passage is likely to bring significant economic benefits by reducing transport costs, even though (of course) we are currently adapted to its impassability. Warmer winters will reduce the winter death rate in the UK for sure, and this vastly outweighs any plausible estimate of heatwave deaths, at least for a range of modest warmings, even before we start to consider any adaptation to the summer heat. We could of course achieve a similar effect by insulating homes and reducing poverty, of course, but we are already "optimally adapted", right?
To boldly assert as axiomatic that "change = bad" is, I think, rather naive and simplistic. All sorts of (social, economic, technological) changes are inevitable, and the latter two at least have a strong record of bringing substantial (no, massive) benefits. Would anyone be silly enough to argue that these changes are bad because we are adapted to the status quo? While I am sure that some climate changes will increase pressure on some ecosystems and human societies, it seems to me to be a rather more nuanced situation than some of the comments above would indicate. Indeed, if the climate changes are slow and modest enough compared to the other changes, it might be hard to detect their overall effect at all (on human health, wealth and happiness, I mean - of course I'm sure it will be easy to measure environmental parameters that document the climate change itself, indeed this is already clear enough). I'm sure UK residents will have noticed the substantial northward march of maize as a crop in recent years (for cattle fodder). I'm not sure to what extent this is due to politics (subsidies), economics, climate change, breeding of better-adapted varieties, or even just farmers gradually realising that it grows better than they had thought possible. Even if climate change is the largest factor (which I doubt, but it's possible), it is not clear who lost out here, other than perhaps the bugs that prefer to live on kale (or whatever the displaced crop was).
Living as I do in a country where houses are expected to last about 30 years, I find it hard to take seriously any worry that they might not be optimally adapted to the climate 100 years hence (let alone the sea level a few centuries later). Note also that a change in fuel prices would change the optimal amount of insulation irrespective of climate change. Likewise, advances in building materials will likely render current designs somewhat redundant.
Extropians would assert that "change = good" and that we should encourage change unless it is proven harmful. Just to be clear on this, I do not endorse this point of view 100% but the difference in opinion seems as much philosophical as scientific. I think that understanding this POV goes a long way to explaining the differences between the environmentalists and the sceptics (even if it does not excuse the dishonesty of the denialist wing).
I hope this doesn't sound too much like a septic handwave, expecting techology to magically save the day. To the extent that climate change is rapid or substantial (which I will deliberately leave undefined here!), of course it's a threat that should be taken seriously. It is a little scary to think about how dominant the human influence can be, and perhaps a mental model of some hypothetical stasis is a comforting thought in which to ground our personal philosophies. But it would be a mistake to let one's comfort zone unduly colour one's perceptions of reality (or at least, such effects need to be openly considered and one should be prepared to see them challenged).