Dear Editor,

The last half billion years, there have been five major mass extinctions, when the diversity of life on earth is suddenly and dramatically contracted. Scientists are currently monitoring the sixth extinction, predicted to be the most devastating since the asteroid impact that wiped out the dinosaurs. This time around, the cataclysm is us.Since the start of the Industrial Revolution, humans have burned through enough fossil fuels coal, oil and natural gas to add some 365 billion metric tons of carbon to the atmosphere. Deforestation has contributed another 180 billion tons. Each year, we throw up another 9 billion tons or so. As a result, the concentration of carbon dioxide in the air today, a little over 400 parts per million, is higher than at any other point in the past 800,000 years.It is expected that such an increase will produce an eventual average global temperature increase of between 3 1/2 and 7 degrees Fahrenheit, and this will trigger a variety of world-altering events, including the disappearance of most remaining glaciers, the inundation of low-lying islands and coastal cities, and the melting of the Artic ice cap by 2050. But this is only half the story.Human activity has transformed between a third and a half of the land surface of the planet. Most of the world's major rivers have been dammed or diverted, fertilizer plants produce more nitrogen than is fixed naturally by all terrestrial ecosystems, fisheries remove more than a third of the primary production of the oceans' coastal waters, humans use more than half of the world's readily accessible fresh water.Population: "Anyone whose major concern is the sanctity of human life is in effect, by leaving population growth unchecked, ensuring death by famine. Nature is pitiless, and if humans will not themselves limit population then they will have it done for them."The most vulnerable point of the Earth is the atmosphere, which acts like a giant mirror, absorbing 95 percent of the sun's energy. If we don't protect the atmosphere, ultraviolet radiation will fry us like ants under a magnifying glass. In the past half century, this precious atmosphere of ours has thinned by 40 percent. And this worries me because in the same time frame, my hair has thinned by 40 percent. It worked out for me, but the Earth may not be so lucky.The Universe: "It is, indeed, only because of the frightening emptiness elsewhere that we are bound to be impressed by the apparently unique and beautiful conditions that have allowed intelligent life to occur on earth.""The natural order does not respond to prayer or propitiation: It maintains its extraordinary regularity. This may not rule out a certain nonspecific deism or pantheism, but it does make nonsense of the idea of a god to which human beings can address themselves."FreethinkerJoseph L. KopernaTamaqua