Global Environmental Degradation and Biodiversity Loss: Implications for Human Health

ERIC CHIVIAN

"The Planet is not in jeopardy. We are in jeopardy. We haven't got the power to destroy the planet—or to save it. But we might have the power to save ourselves."

—Michael Crichton, Jurassic Park (1990)

Introduction

There is abundant evidence that we are beginning to alter, for the first time in history, the chemistry and physics and physiology of the Earth. A basic understanding of biological systems and their dependence on the environment should alert people to the potential dangers these alterations pose for human beings. Yet, most people, including most policymakers, do not comprehend the human implications of global environmental change. Underlying this lack of comprehension is the widespread belief that human beings are separate from the environments in which they live, that they can change the atmosphere and oceans—and damage marine, aquatic, and terrestrial ecosystems in the process—without these changes affecting them.

In focusing on the human health dimensions of biodiversity loss, this volume helps people understand that human beings are an integral part of the environment, and that to protect their health and lives, and those of their children, people must learn to protect the environment.

This chapter will provide an overview about how environmental degradation leads to biodiversity loss, and what the implications of this loss are for human beings. This is an enormously complex topic, one that is in its infancy in terms of scientific understanding. Much of what can be said about it is uncertain and speculative. But the subject is also perhaps the most important one of all—namely the ways that global ecosystems support human health and make human life possible, and there is enough evidence available in the scientific and medical literature to justify looking at possible future scenarios, especially as they may serve as warnings.

Medicine brings a new perspective to discussions about global environmental change. It has a long tradition of acting decisively to prevent life threatening situations from occurring even when all the evidence is not in. The low threshold for performing appendectomies is a case in point (Gross 1956)—if surgeons waited until they were absolutely certain that their patients had appendicitis, it would often be too late to prevent serious illness and death. This is the situation we face today with global environmental degradation. If we wait until we have definite proof of its occurrence and of its consequences, it may be too late to avoid a medical catastrophe.

This chapter will cover the contributions to biodiversity loss from:

• global climate change,

• stratospheric ozone depletion,

• toxic substances in the environment, and

• habitat destruction;

and the possible effects on human health from this loss, including:

• the loss of medicines,

• the loss of medical models, and

• the emergence and spread of infectious diseases.

Central to these discussions will be two themes:

1. That the study of species and biodiversity may be the best means we have for recognizing future danger signals to human health from global environmental degradation, as some species may be so uniquely sensitive to specific assaults on the environment that they may serve as our "canaries," or so-called "indicator species."

2. That we must focus much greater attention on biodiversity loss, which looms as a slowly evolving, potential medical emergency of unprecedented proportions, still largely unappreciated by policymakers and the public.

When Homo sapiens evolved, some 100,000 years ago, the number of species on Earth was the largest ever, but current rates of species extinction resulting from human activities, at least 1000 times those that would have occurred naturally, rivalling the great geologic extinctions of the past, may be reducing these numbers to the lowest levels since the end of the Age of Dinosaurs, 65 million years ago (Wilson 1993). Paul Ehrlich and E.O. Wilson (1991) and others have predicted that one-quarter of all species now alive may become extinct during the next 50 years if these rates of extinction continue.

There are 100 times more people on Earth than any land animal of comparable size that ever lived, and we are the most voracious and destructive species that ever existed. We consume or destroy or co-opt, for example, as much as 40% of all the solar energy trapped by land plants (Ehrlich and Wilson 1991). Not only is this behavior morally indefensible, endangering in the process countless other species, it is fundamentally and ultimately self-destructive.

Several aspects of global environmental degradation have an impact on species populations and biodiversity. This chapter will briefly review some of the evidence.

Global Climate Change

The Intergovernmental Panel on Climate Change (IPCC), the United Nations working group of 2500 of some of the world's most eminent atmospheric, physical, and biological scientists, has stated that projected worldwide CO2...