It seems to me that Contraction and Convergence is the basic principle that should guide climate policy, and that this policy is really unchallenged in principle by any of the climate models under discussion.

Granted that it is good to have accurate models of how the world works, and to work out the numerical balances of C&C.

Nevertheless, I wonder at what point complex and uncertain empirical models become a distraction from simple first principles?

C&C is a necessary condition for a just and sustainable world."

With best wishes and admiration for your and your colleagues' important work on C&C,


This question was the theme of a short speech I gave some years ago to the American Meteorological Society.

Herman Daly
Emeritus Professor

niversity of Maryland

Implications of systematic caps on natural resources

A lasting prosperity requires a much closer attention to the ecological limits of economic activity. Identifying and imposing strict resource and emission caps is vital for a sustainable economy. 

The contraction and convergence model developed for climate- related emissions should be applied more generally. Declining caps on throughput should be established for all non-renewable resources. Sustainable yields should be identified for renewable resources.

Limits should be established for per capita emissions and wastes. Effective mechanisms for imposing caps on these material flows should be set in place. Once established, these limits need to be built into the macro-economic frameworks.

Building a Sustainable and Desirable Economy-in-Society-in-Nature

Robert Costanza
Ida Kubiszewski

Carol Franco
Institute for Sustainable Solutions,
Portland State University

Gar Alperovitz
The Democracy Collaborative and Department of Government and Politics,
University of Maryland

Herman Daly
School of Public Affairs,
University of Maryland

Joshua Farley
Department of Community Development and Applied Economics,
and Gund Institute for Ecological Economics,
University of Vermont

Tim Jackson
Sustainable Lifestyles Research Group,
University of Surrey, UK

Juliet Schor
Department of Sociology,
Boston College

Peter Victor
Faculty of Environmental Studies,
York University, Canada

Ronald Colman
Genuine Progress Index Atlantic,
Nova Scotia, Canada

Report to the United Nations for the 2012 Rio+20 Conferenceas part of the Sustainable Development in the 21st Century (SD21) project implemented by the Division for Sustainable Development of the United Nations Department of Economic and Social Affairs


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