From the point of view of the global economy, the IPCC report can be summarized thus: The energy infrastructure of the planet's economy proves to carry big and growing costs (the ecological, societal, and economic impact of climate change).
As in any case when a technology or resource proves to have high attached costs, we have three (not mutually exclusive) ways to deal with this issue:
We can reduce our use of the technology, in this case by greater energy efficiency and lessened consumption. There are important reasons why this should be done -some energy efficiency measures are self-financing even in the absence of costs associated with climate change, and reduced fossil fuel consumption will somewhat delay and reduce the scale of climate change- but it's important to note that this is problem mitigation, not a solution. Most energy used in a city -where most humans live- isn't spent on what you might call "energy luxuries", but on the very infrastructural and industrial processes that make it possible for us to live, in the mean, better than our grandparents did. You can take a single house off the grid, but what about Rio de Janeiro, or an entire industrial belt? By and large, "green" means "relatively not so bad as the usual," not "sustainable in a way scalable to a multi-billion global society who doesn't particularly want to go back to farming and occasional plagues as a way of life."
An alternative is to learn to live with the associated costs in the most efficient way possible: preparing our infrastructure for more frequent extreme events, strengthening food production and distribution networks to smooth food supply variability, figuring out a way to deal with migratory and epidemiological patterns triggered by shifting climate patterns, etc. It's difficult and expensive, but, as no matter what we do now, it's certain that climate patterns will shift, doing this makes sense. On the other hand, it's again problem mitigation, not solution. We don't have the technology or the resources to deal with long-term climate disruption in a purely reactive way.
The third alternative, of course, is finding alternate sources of energy. Renewable sources like wind and solar energy are the most popular, although I'm not sure we can support existing -not to mention rising- energy demand using them; in the long term, probably something like widespread nuclear or fusion technology (once it's available) will be necessary to take the torch from fossil fuels. In any case, shifting the global economy's energy sources will, at best, be staggeringly costly and rather slow. There's no choice but doing it, but it won't happen overnight, it won't be easy - and it won't shield us from the backlash of our past and current technologies.
In a best case scenario, a mixture of those strategies would be best: massive research and development on alternate energy sources, while temporary energy conservation and impact mitigation measures are taken to weather (no pun intended) the transition period.
In a realistic scenario, though... There are two interrelated strategic problems standing on the way of a reasonable, effective response:
- Symbolic conservation measures (like California's amusingly named "How Many Legislators Does it Take to Change a Light Bulb Act") deliver a lot of the political benefits of a climate-conscious policy with few of the costs. Conservation by itself doesn't work -and much less if it's only implemented piecemeal- but, from the point of view of politicians, that's not a big concern. Much like saving the pandas, it might not be realistically relevant policy, but it sure looks good.
- Disaster preparedness measures benefits those who spend money on them, while technology replacement will be very expensive, and (until it's surpasses the convenience of fossil fuels) won't benefit anybody until most countries invest on it. Hence, more money will be spent on the former than on the latter, despite disaster preparedness being only an stopgap measure.
So far, the response to the IPCC report doesn't give me much hope about a global, effective response to this problem. We dropped the ball once on climate change, delaying so much its near-unanimous recognition as a global policy problem. We better get the solution right.