The Stern Review Report on the Economics of Climate Change
is must reading. The summary of conclusions is at http://www.hm-treasury.gov.uk/media/8A8/C1/Summary_of_Conclusions.pdf
The full report can be read at http://www.hm-treasury.gov.uk/independent_reviews/stern_review_economics...
This report from the British government strongly states that although it will cost us to make necessary changes to reduce greenhouse emissions, the costs are much less than the cost will be to deal with the consequences of unabated climate change. They estimate that if we [and by "we" they mean everyone -- it IS a global problem] don't act soon and forcefully the world will be facing a major upheaval on the scale of a world war or the great depression.
The full report is in six sections:
Climate change: our approach
Impacts of climate change on growth and development
Economics of stabilisation
Policy responses for mitigation
Policy responses for adaptation
International collective action