Top banner


Pimm's Audit

Peter McEvoy

The World According to Pimm: A Scientist Audits the Earth. Stuart L. Pimm. xvi + 285 pp. McGraw-Hill, 2001. $24.95.

The World According to Pimm is a global natural history, a comprehensive accounting of the impact of human beings on the planet Earth. Here noted ecologist Stuart Pimm has distilled the numbers that we need to have at our fingertips at the start of the new century. Pimm's many scientific contributions to population and community ecology allow him to speak with authority on those subjects.

This book also reveals a personal side to Pimm: He is a consummate storyteller, a connoisseur of good food and wine, an opera buff. Like most ecologists, he does research in exotic locations around the world, but he prefers the lower latitudes, believing that Michigan is "closer to the North Pole than any sensible species should live."

The book is divided into three parts that deal respectively with the land (and water), the oceans and the variety of life. In each part he examines the big issues to come up with the numbers essential to any dialogue about our future. Each number in his reckoning becomes another line in a spreadsheet that holds the world's biological accounts. He helps us understand how ecologists get such numbers and what confidence we can have in them.

Land covers roughly one-third of the Earth's surface but generates 99 percent of our food. Humans consume, directly or indirectly, about 42 percent of global plant production, leaving precious little to feed the biosphere. We consume nearly 60 percent of the accessible water runoff each year. About 90 percent of the ocean is unproductive, supporting fisheries that require only 2 percent of the open oceans' plant productivity. Even at this modest level of exploitation, we are overharvesting these stocks. In the more productive areas of the ocean, the remaining 10 percent, we harvest fisheries that require 35 percent of local plant production, causing widespread decline. Whether we are talking about fisheries, farmland or forests, we have used up the easy and profitable natural resources (the Earth's accounts bearing the highest interest), leaving only the more difficult and less profitable ones (accounts bearing the least interest).

We are fast diminishing the variety of life. At the natural, background rate of extinction, averaged over tens of million of years, no more than 1 species in 1 million or more should go extinct per year. The unnatural rate generated by human impact is between 100 and 1,000 times the natural rate. Many of the world's species are concentrated in areas known as "hotspots" that should be protected as preserves. When human activity impinges on hotspots, species become extinct in unusually high numbers. Pimm does not address a lingering question: If global warming were to push species out of these preserves and hotspots, would there be suitable habitat to accommodate them? Pimm's accounting explores the uncertainties involved in finding, naming and cataloguing species in the book of life, but his treatment of biodiversity focuses too much attention on counting species. Biodiversity is a broader concept, encompassing the variety of life at all levels from genes to ecosystems, and we must reckon with loss in life's variety in all its forms.

News about the environment can be terribly depressing, yet this book is unashamedly optimistic. It celebrates our spectacular and fascinating natural world. And it tells us precisely how we got into our environmental predicament and how we might achieve more- sustainable, nondestructive use of the environment in the future.

The chapter on "The Wisdom to Use Nature's Resources" is a particularly incisive summary of how and why we find ourselves overexploiting the natural resources on which we and the rest of Earth's creatures depend. Individuals are taking profit from a common stock without bearing the costs of damage to it. When a valuable biotic resource like caviar becomes rare, its price goes up, and perversely, so do the incentives to acquire it. Any resource that does not generate a rate of return that exceeds what the money would yield if invested elsewhere doesn't have a future and will likely be liquidated. "Perverse subsidies" prop up otherwise unprofitable enterprises in fisheries, forestry and farming, encouraging damage to natural resources. The vagaries of nature and rare, unforeseen events make it difficult to adjust harvest to the sustainable level. Nature is variable, but our response is not—we fail to adjust our consumption to its variations, and the result is overfishing and overgrazing. If we were wise enough to recognize that the consequences are severe declines in natural resources, then we would stop wasting money on actions that damage our global environment and would take up the challenge of finding actions that reconcile ecological, economic and political constraints.

Pimm illustrates for us how unevenly consumers and resources are distributed across the Earth's surface. On land, there are green accounts (warm and wet places covered by forests), yellow accounts (dry places that are deserts and grasslands) and white accounts (cold places atop mountains and at high latitudes). In the oceans, there are barren open seas and teeming continental shelves and areas of upwelling. He reviews which accounts bear the most interest and which are most affected by humans.

This spatial heterogeneity is figured in 13 black-and-white maps at the center of the book. Unfortunately, these are set apart from legends and text, forcing the reader to keep flipping pages to follow the argument. Also unfortunate is the notable absence of tables (except for a few in the endnotes) and graphs.

The synthesis Pimm offers requires courage; it is easy for other scientists to pick apart individual numbers that contribute to a total, without ever offering a total themselves. And it is hard to make long-range predictions from short-range indications. Pimm notes that there are two important questions a global accountant must address: What does the Earth do for us? and What are we doing to the Earth? He provides answers to the latter. Perhaps we can look forward to another book addressing the former, a book that synthesizes current research on the links among biodiversity, ecosystem services and the human economy.—Peter B. McEvoy, Entomology, Oregon State University

comments powered by Disqus


Bottom Banner