The Sixth Great Extinction
Five times in the past half-billion years, the fossil record shows us, living things have been wiped out over much of the earth. Catastrophic changes in climate, or the impact of an asteroid or a comet, are the likeliest causes for the five great extinctions which geologists and palaeobiologists have identified, ranging from the Ordovician-Silurian extinction, of about 439 million years ago, to the Cretaceous-Tertiary (K/T} extinction of 65 million years ago, when the dinosaurs disappeared [1].
What is the rate of extinction? The normal "background rate of extinction is roughly 1-2 species per year." Reference
"Paleontologists estimate the background rate of species extinction--the long-term extinction rate exhibited prior to humanity's influence--at between 1 and 10 extinctions each decade among every million fossil species. Assuming from a variety of estimates that 10 million species are alive today (Stork 1993 and 1997, May 1988, Hammond 1992), scientists can expect from 1 to 10 species to go extinct each year from all forms of life, visible and microscopic. In fact, species are exiting much faster. Based on records of extinction among the best- studied types of animals, ecologist Stuart Pimm and colleagues calculated extinction rates during the past century to range from 100 to 10,000 species per year (again, assuming 10 million species exist). That rate is between 100 and 1000 times faster than the background rate of species extinction (Pimm et al 1995)." Reference - Bold mine. Extinction rates in the tropics are based on rates of deforestation.
Unfortunately "the Earth needs, on average, about 10 million years to recover from global extinctions".
"If we substantially diminish biodiversity on Earth, we can't expect the biosphere to just bounce back. It doesn't do that. The process of diversification is too slow", "The planet would be biologically depleted for millions of years, with consequences extending not only beyond the lives of our children's children, but beyond the likely lifespan of the entire human species." Evolutionary "Speed Limit"
Humans are causing extinctions through a variety of means including habitat destruction, hunting and poaching, the introduction of non-native species, pollution and climate change.
Concerning Global Warming alone we read that:
"International scientists from eight countries have warned that, based even on the most conservative estimates, rising temperatures will trigger a global mass extinction of unprecedented proportions [2],[3].
They said global warming will set in train a far bigger threat to terrestrial species than previously realised, at least on a par with the already well-documented destruction of natural habitats around the world.
It is the first time such a powerful assessment has been made and its conclusions will shock even those environmentalists accustomed to "worst-case" scenarios." [1]
"the corporate media's long-term, stubborn refusal to address the real issues behind global warming - the corporations fighting with unrelenting ferocity to destroy not just the Kyoto protocol but the environment movement itself - represents the ultimate betrayal of us, our future, and our planet." [2]
The Sixth Great Extinction is avoidable - if we act now.[3]
"We are predicting the extinction of about two-thirds of all bird, mammal, butterfly and plant species by the end of the next century, based on current trends." Peter H. Raven, 2002 President of AAAS, the American Association for the Advancement of Science.
(1) The Five Worst Extinctions in Earth's History
(2) Feeling the heat: Climate change and biodiversity loss
(3) Never Mind That Boiling Kettle
