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An ambitious plan to leverage existing solutions to global warming is short on analytic rigor

Drawdown: The Most Comprehensive Plan Ever Proposed to Reverse Global Warming

Paul Hawken, Ed.
Penguin Books
256 pp.
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In Drawdown, entrepreneur Paul Hawken and colleagues introduce an ambitious project to build a social movement around a science-based plan to reduce the concentration of greenhouse gases in the atmosphere. The new volume is a handsome collection of short essays identifying what Hawken and his collaborators believe to be the 80 most effective actions that can jointly reduce emissions and sequester atmospheric carbon in soils and vegetation.

The diverse initiatives described in the book include advances in energy storage, wider adoption of composting, the creation of more walkable cities, the cultivation of perennial crops for bioenergy, and cement made from greener components.

The 80 actions, already taking place around the globe, are described in short texts illustrated by photographs. Each is also represented by four numbers: reduction in greenhouse gas (GHG) emissions; implementation cost; operational savings over a 30-year lifetime, relative to business as usual; and rank order according to its GHG drawdown potential. A subsequent section includes 20 possible game-changers, including a proposed experiment to sequester carbon by returning grasses to subpolar regions.

The authors estimate that, combined, the first 80 initiatives could reduce emissions by about 1000 gigatons. The four actions that they conclude have the greatest potential for reducing greenhouse gases—the phasing out of hydrofluorocarbons (HFCs) as chemical refrigerants, the proliferation of onshore wind turbines, a reduction in food waste, and a global shift to a diet rich in plants—account for more than 30% of the total avoided emissions.

The reader is told several times that the Drawdown project is based on measurement, mathematics, and rigorous modeling by scientists and researchers, but this is a case that remains to be made. The photo in the section called “Numbers” illustrates the dilemma. It is a visually intriguing collage of 20 tables of figures and their graphical display. However, it is only symbolic. It is too small to allow the reader to examine the content.

The Drawdown team multiplies a handful of numbers by a scale factor for each action and scenario; then the results for all 80 actions are (essentially) added together to represent the scenario. However, this approach to scaling up ignores the profound differences among regions.
The all-important physical and economic interdependencies among the 80 actions also require attention. These include competition over access to up-front capital to fund new infrastructure and over potentially scarce resources that will be in growing demand.

Equally important are the effects of cost reductions for realizing one type of action—the use of alternative cement, for example—on cost savings for other actions, namely all those requiring built infrastructure. A model of the world economy that is based on a considerably more detailed and conceptually structured representation can capture these material and cost interrelationships among sectors and geographies.

Researchers at the intersection of input-output economics and industrial ecology are working with the kinds of models that would better substantiate this project’s methodological claims. A colleague and I, for example, recently examined the implications of moving toward plant-based diets and ultimately reached conclusions different from those reached by the authors of Drawdown (1).

No one expects a social movement to be based on a state-of-the-art mathematical-modeling framework. Yet it is on the authority of model-based numerical results that Drawdown transforms a long list of individual actions into an integrated strategy.

I suggest two paths that could strengthen the project’s methodological claims. One is to invite a panel of modelers to assess its analytic approach and make recommendations for next steps. Another is to make more modest claims about models and scientific rigor and instead rely more heavily on informed consensus. Tentative results and the associated assumptions could be reviewed by a panel with the aim of ordering priorities and agreeing on what are, in any case, only roughly estimated total impacts.

If the authors are successful in launching a social movement around the ambitious ideas described, this could inspire the wider research community to take on more visionary scenarios, an outcome that could in turn help advance the project’s overall objectives.


  1. N. Springer, F. Duchin, Environ. Sci. Technol. 48, 8 (2014).

About the author

The reviewer is at the Department of Economics, Rensselaer Polytechnic Institute, Troy, NY 12180, USA.