Effects of Climate Change on People and Other Species

James Hansen has written an article for the New York Review of Books. His article is better than my summary.

First, the other species:

Studies of more than one thousand species of plants, animals, and insects, including butterfly ranges charted by members of the public, found an average migration rate toward the North and South Poles of about four miles per decade in the second half of the twentieth century. That is not fast enough. During the past thirty years the lines marking the regions in which a given average temperature prevails (“isotherms”) have been moving poleward at a rate of about thirty-five miles per decade…

As long as the total movement of isotherms toward the poles is much smaller than the size of the habitat, or the ranges in which the animals live, the effect on species is limited. But now the movement is inexorably toward the poles and totals more than a hundred miles over the past several decades. If emissions of greenhouse gases continue to increase at the current rate—”business as usual”—then the rate of isotherm movement will double in this century to at least seventy miles per decade. If we continue on this path, a large fraction of the species on Earth, as many as 50 percent or more, may become extinct.

Hansen mentions the previous mass extinctions that accompanied temperature increases of up to 10 F,

when between 50 and 90 percent of the species on Earth disappeared forever. In each case, life survived and new species developed over hundreds of thousands of years. The most recent of these mass extinctions defines the boundary, 55 million years ago, between the Paleocene and Eocene epochs. The evolutionary turmoil associated with that climate change gave rise to a host of modern mammals, from rodents to primates, which appear in fossil records for the first time in the early Eocene.

If human beings follow a business-as-usual course, continuing to exploit fossil fuel resources without reducing carbon emissions or capturing and sequestering them before they warm the atmosphere, the eventual effects on climate and life may be comparable to those at the time of mass extinctions. Life will survive, but it will do so on a transformed planet. For all foreseeable human generations, it will be a far more desolate world than the one in which civilization developed and flourished during the past several thousand years.

What about the direct effect on people, outside of our need for and appreciation of other species? If the temperature rises 3 C this century, 5 F, sea level is likely to rise 80 ft. There go the East Coast cities: Boston, New York, Philadelphia, Washington, and pretty much all of Florida. One sixth of Americans live less than 80 ft above our current sea level. In China, 250 million people live below that new sea level, Bangladesh 120 million (out of 140 million), and India 150 million. This process would begin slowly, then (according to evidence from past ice sheets), sea level could rise 1 meter/40 inches, every 20 years.

The increase in melting is already being seen. Summer icequakes in Greenland registering at least 4.6 on the Richter scale, from the ice lurching forward and then stopping, have quadrupled since 1993.

The alternate scenario, the one where we are responsible and cut our emissions, leveling off this decade and then decreasing rapidly over 3 decades,

with (added) global warming under two degrees Fahrenheit, still produces a significant rise in the sea level, but its slower rate, probably less than a few feet per century, would allow time to develop strategies that would adapt to, and mitigate, the rise in the sea level.

Moreover, things could get really serious if warming this century is as little as 3 – 4 F, then,

all bets are off.

The 55 million year ago mass extinction was caused, it is thought, by the release of frozen methane hydrates (natural gas frozen into water) in the Arctic, and it may warm enough before this century is over to release significant amounts. If this happens, we cannot create a good scenario no matter what we do.

We need to level greenhouse gas emissions by 2015 and then cut them rapidly afterwards.

Questions: What are you hearing in the media about the degree and speed of needed reductions? Are you hearing that since 30% of cumulative GHG emissions are American and since we’re richer, that we will pay for much of the developing world to shift to lower carbon energy sources, and that Europe will have to as well?

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