Humanity Is Taking More
Than Earth Can Give

Researchers Calculate
The Planet Is Ecologically Overburdened By 20 Percent

by Carl T. Hall

Nobody doubts that people put a heavy burden on the biosphere. Now, a global team of ecology experts, working under the sponsorship of famed Harvard biologist Edward O. Wilson, has tried to weigh just how heavy the load might be.

The bottom line is a single, sobering number: 120 percent.

Adding up all the farming, fishing, mining, building and fuel consumption, researchers calculated our global ecological demand to be the equivalent of 120 percent of the Earth's capacity to sustain these activities.

Operating 20 percent beyond the break-even point means that "it would require 1.2 Earths, or one Earth for 1.2 years, to regenerate what humanity used in 1999," the researchers conclude in a study appearing today in the Proceedings of the National Academy of Sciences. The analysis is based on 1999 statistics, the most recent available, and generally accepted estimates of the planet's biological productivity.

Our "ecological overshoot" started in the late 1970s and continues to widen, the researchers added. During an interview Monday, Wilson said the new study offered one of the first impartial methods of keeping tabs on the biosphere.

"This is a very effective measure for telling the world where we are and what the trajectory might be," Wilson said. "We've never really had anything like this before -- a measure we can intuitively understand and that's based on solid data."

The study is also one of the latest attempts by ecology specialists to use some of the standard tools of economics, transforming fisheries, forests and other key elements of the biosphere into so much "natural capital."

The idea is to monitor the ebbs and flows of this form of capital with much the same kind of numerical rigor that economists use in tracking labor, investment and industrial output.

"We need accounts for our use of nature, the same as we use accounts in business," said Mathis Wackernagel, program director at the Oakland-based group Redefining Progress and lead author of the new study.

Co-authors include Norman Myers of Oxford University, Jorgen Randers at the Norwegian School of Management and Richard Norgaard at UC Berkeley.

The authors shied away from any specific policy choices that might reduce the shadow cast by humanity's huge "ecological footprint." But they made it clear that in their view current consumption patterns could not be sustained.

Worldwide, the average amount of productive land needed to satisfy the needs and wants of each man, woman and child is about 2.3 "global hectares" -- the standardized measure of productive acreage used by the study authors. By comparison, the productive capacity of the Earth is estimated at 1.9 hectares per capita.

The imbalance is much more pronounced, of course, in the richest countries: The United States, for instance, consumed about 9.7 global hectares per person for 1999, while the United Kingdom commanded 5.4, and Germany took 4.7.

"We are overspending," Wackernagel said, calling the trend a prescription for "ecological bankruptcy" that is starting to show up already in collapsing commercial fisheries, loss of productive cropland and demise of natural forests.

But conservative critics said the study amounted to little more than fancy guesswork, saying there were no data to justify the implication that human activity was running roughshod over the planet's health.

"I think this is another one of these scare tactics" from environmentalists, said Thomas Gale Moore of the Hoover Institution in Palo Alto. "They come to the conclusion that mankind is already using 120 percent of the Earth's capacity. But if that were true, I would think we'd be seeing a general degradation of the world, when in fact the environment, certainly in the advanced countries of the world, is getting cleaner and better, not dirtier."

The new study drew mostly from national production and land-use statistics already being prepared by governments around the world. In the new framework, these statistics become fodder for a kind of "ecological GDP" -- a single number to sum up all the best available "biophysical indicators" to track resources and the sustainability of the human economy.

"The purpose of these global accounts is not merely to illustrate a method for measuring human demand on bioproductivity, but to offer a tool for measuring the potential effect of remedial policies," the authors conclude.

Just what form those policies might take is a matter the researchers are leaving to policymakers to decide. They said any such decisions were being made in a vacuum without some fair way to keep score.

"Assessments like the one presented here allow humanity, using existing data, to monitor its performance regarding a necessary ecological condition for sustainability: the need to keep human demand within the amount that nature can supply," the study stated.

email Carl T. Hall at: mailto:chall@sfchronicle.com

Source: http://tinyurl.com/3kstt