The final reality is perhaps the most important:

The macroeconomic costs of this carbon revolution are likely to be manageable, being in the order of 0.6–1.4 percent of global GDP by 2030. To put this figure in perspective, if one were to view this spending as a form of insurance against potential damage due to climate change, it might be relevant to compare it to global spending on insurance, which was 3.3 percent of GDP in 2005. Borrowing could potentially finance many of the costs, thereby effectively limiting the impact on near-term GDP growth. In fact, depending on how new low-carbon infrastructure is financed, the transition to a low-carbon economy may increase annual GDP growth in many countries.

I am reprinting the cost curve here, because MGI have provided a much bigger version of it (click to enlarge):

The report notes that "we have been fairly conservative in our assumptions about technological progress in these projections." For instance, the analysis appears to ignore the potential of concentrated solar thermal electricity entirely (see "The best technology to protect the earth").

Finally, although McKinsey is a classic market-oriented business consulting company, the report offers a realistic assessment of the policies needed to achieve our crucial low-carbon future:

The microeconomic changes needed to increase carbon productivity at the levels required will not occur without the active leadership and collaboration of governments and businesses globally. We need new policies, regulatory frameworks, and institutions focused on four areas: creating market-based incentives to innovate and raise carbon productivity; addressing market failures that prevent abatement opportunities from being captured profitably; resolving issues of allocation and fairness, in particular between the developed and developing worlds and between industry sectors; and accelerating progress to avoid missing critical emissions targets.

The entire report is well worth reading.

This post was created for ClimateProgress.org, a project of the Center for American Progress Action Fund.