Executive Summary
Global Change and the Earth System: A Planet Under Pressure
11/11/2009
- Opinión
foreword
The relationship of humans with the Earth’s environment has changed throughout the evolution of Homo sapiens and the development of societies. For virtually all of human existence on the planet, interaction with the environment has taken place at the local, or at most the regional, scale. The environment at the scale of the Earth as a whole - the passing of the seasons, the vagaries of weather and climate, the ebbing and flowing of river systems and glaciers, the rich diversity of life in all its forms - has been something within which people have had to operate, subject only to the great forces of nature and the occasional perturbations of extraterrestrial origin. Earth’s environment has been a bountiful source of resources as well as a remarkably stable life support system that has allowed human civilisations to develop and flourish.
A profound transformation of Earth’s environment is now apparent, owing not to the great forces of nature or to extraterrestrial sources but to the numbers and activities of people - the phenomenon of global change. Begun centuries ago, this transformation has undergone a profound acceleration during the second half of the 20th century. During the last 100 years human population soared from little more than one to six billion and economic activity increased nearly 10-fold between 1950 and 2000. The world’s population is more tightly connected than ever before via globalisation of economies and information flows. Half of Earth’s land surface has been domesticated for direct human use. Most of the world’s fisheries are fully or over-exploited. The composition of the atmosphere - greenhouse gases, reactive gases, aerosol particles - is now significantly different than it was a century ago. The Earth is now in the midst of its sixth great extinction event. The evidence that these changes are affecting the basic functioning of the Earth System, particularly the climate, grows stronger every year. The magnitude and rates of human-driven changes to the global environment are in many cases unprecedented for at least the last half-million years.
This executive summary describes a book that sets out what is known about global change and the nature of the Earth System. It addresses a number of important but difficult questions. How does the Earth System operate in the absence of significant human influence? How can human-driven effects be discerned from those due to natural variability? What are the implications of global change for human well-being? How robust is the Earth System in the face of this new internal force of change? Can human activities trigger abrupt and potentially irreversible changes to which adaptation would be impossible? How serious is this inadvertent human experiment with its own life support system?
Will Steffen, Angelina Sanderson, Peter Tyson, Jill Jäger, Pamela Matson, Berrien Moore III, Frank Oldfield, Katherine Richardson, John Schellnhuber, B.L. Turner II, Robert Wasson
https://www.alainet.org/fr/node/137640?language=es
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