Re: Six Degrees of Separation: Looking Backward at Climates Past, and Forward to a Worst-Case Scenar

The Guardian, April 23, 2007

http://environment.guardian.co.uk/climatechange/story/0,,2063400,00.html

Six steps to hell

By the end of the century, the Earth could be more than 6C hotter

than

it is today, according to the Intergovernmental Panel on Climate

Change. We know that would be bad news - but just how bad? How big a

rise will it take for the Alps to melt, the oceans to die and desert

to conquer Europe and the Americas?

Mark Lynas sifted through thousands of scientific papers for his new

book on global warming. This is what the research told him ...

Monday April 23, 2007

The Guardian

A dead pelican in a drought in Mexico. Photograph: Eduardo Resendiz/

EPA

Nebraska isn't at the top of most tourists' to-do lists. However,

this

dreary expanse of impossibly flat plains sits in the middle of one of

the most productive agricultural systems on Earth. Beef and corn

dominate the economy, and the Sand Hills region - where low, grassy

hillocks rise up from the flatlands - has some of the best cattle

ranching in the whole US.

But scratch beneath the grass and you will find, as the name

suggests,

not soil but sand. These innocuous-looking hills were once desert,

part of an immense system of sand dunes that spread across the Great

Plains from Texas in the south to the Canadian prairies in the north.

Six thousand years ago, when temperatures were about 1C warmer than

today in the US, these deserts may have looked much as the Sahara

does

today. As global warming bites, the western US could once again be

plagued by perennial drought - devastating agriculture and driving

out

human inhabitants on a scale far larger than the 1930s "Dustbowl"

exodus.

On the other side of the Atlantic, today's hottest desert could be

seeing a wetter future in the one-degree world. At the same time as

sand dunes were blowing across the western US, the central Sahara was

a veritable Garden of Eden as rock paintings of elephants, giraffes

and buffalo, also dating from 6,000 years ago, attest.

On the borders of what is today Chad, Nigeria and Cameroon, the

prehistoric Lake Mega-Chad spread over an area only slightly smaller

than the Caspian Sea does now.

Could a resurgent north African monsoon drive rainfall back into the

Sahara in a one-degree world? Models suggest it could.

Also in Africa, Mount Kilimanjaro will be losing the last of its snow

and ice as temperatures rise, leaving the entire continent ice-free

for the first time in at least 11,000 years.

The Alps, too, will be melting, releasing deadly giant landslides as

thawing permafrost removes the "glue" that holds the peaks together.

In the Arctic, temperatures will rise far higher than the one-degree

global average, continuing the rapid decline in sea ice that

scientists have already observed.

This spells bad news for polar bears, walruses and ringed seals -

species that are effectively pushed off the top of the planet as

warming shrinks cold areas closer and closer to the pole.

Indeed, it is the ecological effects of warming that may be most

apparent at one degree. Critically, this temperature rise may wipe

out

the majority of the world's tropical coral reefs, devastating marine

biodiversity. Most of the Great Barrier Reef will be dead.

In the highly unlikely event that global warming deniers prove to be

right, we will still have to worry about carbon dioxide, because it

dissolves in the oceans and makes them more acidic.

Even with relatively low emissions, large areas of the southern

oceans

and parts of the Pacific will within a few decades become toxic to

organisms with calcium carbonate shells, for the simple reason that

the acidic seawater will dissolve them.

Many species of plankton - the basis of the marine food chain and

essential for the sustenance of higher creatures, from mackerel to

baleen whales - will be wiped out, and the more acidic seawater may

be

the knockout blow for what remains of the world's coral reefs.

The oceans may become the new deserts as the world's temperatures

reach 2C above today's.

Two degrees may not sound like much, but it is enough to make every

European summer as hot as 2003, when 30,000 people died from

heatstroke. That means extreme summers will be much hotter still.

As Middle East-style temperatures sweep across Europe, the death toll

may reach into the hundreds of thousands. The Mediterranean area can

expect six more weeks of heatwave conditions, with wildfire risk also

growing.

Water worries will be aggravated as the southern Med loses a fifth of

its rainfall, and the tourism industry could collapse as people move

north outside the zones of extreme heat.

Two degrees is also enough to cause the eventual complete melting of

the Greenland ice sheet, which would raise global sea levels by seven

metres. Much of the ice-cap disappeared 125,000 years ago, when

global

temperatures were 1-2C higher than now.

Because of the sheer size of the ice sheet, no one expects this full

seven metres to come before the end of the century, but a top Nasa

climate scientist, James Hansen, is warning that the mainstream

projections of sea level rise (of 50cm or so by 2100) could be

dangerously conservative.

As if to underline Hansen's warning, the rate of ice loss from

Greenland has tripled since 2004.

This melting will also continue to affect the world's mountain

ranges,

and in Peru all the glaciers will disappear from the Andean peaks

that

currently supply Lima with water.

In California, the loss of snowpack from the Sierra Nevada - three-

quarters of which could disappear in the two-degree world - will

leave

cities such as Los Angeles increasingly thirsty during the summer.

Global food supplies, especially in the tropics, will also be

affected

but while two degrees of warming will be survivable for most humans,

a

third of all species alive today may be driven to extinction as

climate change wipes out their habitat.

Scientists estimate that we have at best 10 years to bring down

global

carbon emissions if we are to stabilise world temperatures within two

degrees of their present levels.

The impacts of two degrees warming are bad enough, but far worse is

in

store if emissions continue to rise. Most importantly, 3C may be the

"tipping point" where global warming could run out of control,

leaving

us powerless to intervene as planetary temperatures soar.

The centre of this predicted disaster is the Amazon, where the

tropical rainforest, which today extends over millions of square

kilometres, would burn down in a firestorm of epic proportions.

Computer model projections show worsening droughts making Amazonian

trees, which have no evolved resistance to fire, much more

susceptible

to burning. Once this drying trend passes a critical threshold, any

spark could light the firestorm which destroys almost the entire

rainforest ecosystem.

Once the trees have gone, desert will appear and the carbon released

by the forests' burning will be joined by still more from the world's

soils. This could boost global temperatures by a further 1.5