The World According to Pimm: A Scientist Audits the Earth

  • Stuart Pimm
McGraw-Hill: 2001. 304 pp. £18.99, $24.95
Credit: DAVID NEWTON

Those who study global change are well versed in the sobering statistics of the enormous impact of humans on the Earth — the dramatic change in the chemistry of the atmosphere, the massive alteration of the surface of the land, the diversion and despoiling of a large fraction of the available fresh water, the depletion of ocean fisheries, the homogenization of the Earth's biota and the extirpation of large numbers of species. These scientists share a sense of frustration, however, about the fact that the general public and policy-makers are not grasping the significance of these changes nor acting to alter these trajectories for the well-being of future generations. In The World According to Pimm, Stuart Pimm is attempting to enlarge the army of scientists working on these issues and to engage the public in the dialogue about what is happening to the biotic resources of the Earth and how we need to change our trajectory of development in order to build a sustainable world.

To accomplish his task, Pimm has written an engaging and important book. He might well have called it “The World According to Peter, Paul and Pauly as viewed by Pimm”, as the bulk of the book is devoted to an analysis of studies involving Peter Vitousek, Paul Ehrlich and Daniel Pauly. The book takes on a bold challenge — an accounting of the productive capacity of both the land and of the oceans and how humans have modified it. Pimm then documents the extent to which humans are utilizing the available fresh water and, finally, the impact of humans on the biodiversity of the Earth. He uses very simple mathematics and language to drive home the point that humans have very substantially modified the Earth's biotic resources.

The first part of the book is based on the dramatic retelling of the story first published by Vitousek and colleagues in 1986 in BioScience, in which they calculated that humans already use 40% of the primary productivity of the land. That is a sobering figure in view of the projections of growth of the human population during this century. There was some difficulty in getting this penetrating study published, but once it was, it was used widely. For quite a while it was impossible to go to a meeting related to the environment where the statistics of this paper were not used in the opening address. Subsequent attempts to check and recalculate the numbers, as Pimm has done, have borne out the original thesis. Pimm's recalculations are engaging; he does a very good job of making sure that the general reader can clearly understand the basis for these estimates of human use of the biosphere.

The second part of the book deals with human use of the Earth's water resources and builds on work by Ehrlich and his colleagues Sandra Postel and Gretchen Daily. They have shown that humans are using a sixth of the total estimated runoff (50% of that available), and in doing so have drastically altered the Earth's rivers — its plumbing system — especially in the Northern Hemisphere.

The work of Vitousek and colleagues inspired Pauly and a colleague to do a similar study of the human use of the oceans. They estimated that a third of the oceans' production goes to support human fisheries — another stunning number in view of the fact that, not too long ago, the ocean fisheries were considered to be inexhaustible. Large numbers of fisheries are now depleted or endangered. We are clearly at the limits of ocean exploitation. Further, as Pauly and others have shown, we are now “fishing down the food chain”, as the large predatory fish have been depleted.

Pimm concludes his book with a sobering analysis of species losses, his speciality. He ends his analysis with a plea for the preservation of those areas of the world that are particularly rich in species, the so-called 'hot spots'. He claims that we do have the means at hand to “defy nature's end” by purchasing and protecting examples of these areas.

In recent years the international scientific community has made an enormous effort to carefully document, through the International Panel on Climate Change, the impact of humans on the Earth's climatic system. The panel has concluded that human action is indeed altering the climate of the Earth with profound consequences for the way we will live our lives. Pimm does not deal with the consequences of these changes, nor with the escalating disruptions due to the biological homogenization of the Earth's biota. He purposely omitted considering future changes and concentrated on what we know now and for certain. Putting where we are today together with what the future most probably holds for the biotic systems on which we depend certainly gives cause for concern. Let's hope that Pimm's book will educate more of us on what the stakes are and why we need to move urgently towards a more sustainable use of our resources than we are seeing today.