"...Leaders have no excuse – they are elected to lead and to protect the public and its best
interests. Leaders have at their disposal the best scientific organizations in the world, such as the
United Kingdom’s Royal Society and the United States National Academy of Sciences.
Only in the past few years did the science crystallize, revealing the urgency – our planet
really is in peril. If we do not change course soon, we will hand our children a situation that is
out of their control, as amplifying feedbacks drive the dynamics of the global system.
The amount of carbon dioxide in the air has already risen to a dangerous level. The preindustrial
carbon dioxide amount was 280 parts per million (ppm). Humans, by burning coal, oil
and gas have increased carbon dioxide to 385 ppm, and it continues to grow by about 2 ppm per
year.
Earth, with its four kilometer deep ocean, responds only slowly to changes of carbon
dioxide. So more climate change will occur, even if we make maximum effort to slow carbon
dioxide growth. Arctic sea ice will disappear in the summer season within the next few decades.
Mountain glaciers, providing fresh water for rivers that supply hundreds of millions of people,
will disappear – practically all of the glaciers could be gone within 50 years, if carbon dioxide
continues to increase at current rates. Coral reefs, harboring a quarter of ocean species, are
threatened, if carbon dioxide continues to rise.
The greatest threats, hanging like the sword of Damocles over our children and
grandchildren, are those that are irreversible on any time scale that humans can imagine. If
coastal ice shelves buttressing the West Antarctic ice sheet continue to disintegrate, the ice sheet
could disgorge into the ocean, raising sea level by several meters in a century. Such rates of sea
level change have occurred many times in Earth’s history in response to global warming rates no
higher than that of the past thirty years. Almost half of the world’s great cities, and many
historical sites, are located on coast lines.
The most threatening change, from my perspective, is extermination of species. Several
times in Earth’s long history rapid global warming of several degrees occurred, apparently
spurred by amplifying feedbacks. In each case more than half of plant and animal species went
extinct. New species came into being over tens and hundreds of thousands of years. But these
are time scales and generations that we cannot imagine. If we drive our fellow species to
extinction we will leave a far more desolate planet for our descendants than the world that we
inherited from our elders. We will leave a world haunted by the memories of what was..."

http://www.columbia.edu/~jeh1/mailings/2009/20090215_Damocles.pdf