Dr. Alley summarized many estimates of the costs of dealing with climate change in his book Earth: The Operators' Manual. Some of those are repeated here.

The Intergovernmental Panel on Climate Change (IPCC) from 2007 found costs of between slight growth (0.6%) and somewhat larger magnitude shrinkage (3.0%) of global GDP in 2030, versus business-as-usual, for different paths toward stabilizing the atmospheric concentration of CO2 at between 1.6 and 2.5 times the level before the industrial revolution.

IPCC, 2007, Summary for Policymakers, in Metz, B., O. R. Davidson, P. R. Bosch, R. Dave and L. A. Meyer (eds.), Climate Change 2007: Mitigation. Contribution of Working Group III to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (Cambridge University Press, New York).

Much relevant work has been done in Germany. The German Advisory Council on Global Change also considered various rates and levels of stabilization, finding costs centered on about 0.7% of the world economy.

German Advisory Council on Global Change (WBGU) (Grassl, H., J. Kokott, M. Kulessa, J. Luther, F. Nuscheler, R. Sauerborn, H.-J. Schellnhuber, R. Schubert and E.-D. Schulze), 2003, Climate Protection Strategies for the 21st Century: Kyoto and Beyond.

Comparable estimates - average about 1% cost, as low as 1% benefit and as high as 4% costs - were summarized in Hasselmann, K., 2009, 'What to do? Does science have a role?' European Physical Journal Special Topics 176: 37 - 51.)