[Reader-list] impacts precis

[Nagraj Adve]

In recent months, there's been talk, some of it fairly cavalier, of us
crossing the 2 deg C warming mark. The brief list of likely impacts below
as we rise degree by degree should give us pause, even as the farce of
Durban plays out.
When Lynas' book came out, he made clear that he was merely reporting
already published peer-reviewed studies.
It is worrying that we are already on course for some of the feedbacks he
includes; for instance, the melting of Arctic ice. Each feedback will make
others more likely.
Naga


*The impact of temperature rises*



By Mark Lynas, written for the Guardian, 14 April 2009. A slightly updated
precis of

his book Six Degrees



*Less than 2C*

Arctic sea icecap disappears, leaving polar bears homeless and

changing the Earth’s energy balance dramatically as reflective ice is

replaced during summer months by darker sea surface. Now expected by

2030 or even earlier.



Tropical coral reefs suffer severe and repeated bleaching episodes due

to hotter ocean waters, killing off most coral and delivering a hammer

blow to marine biodiversity.



Droughts spread through the sub-tropics, accompanied by heatwaves and

intense wildfires. Worst-hit are the Mediterranean, the south-west

United States, southern Africa and Australia.



*2C-3C*

Summer heatwaves such as that in Europe in 2003, which killed 30,000

people, become annual events. Extreme heat sees temperatures reaching

the low 40s Celsius in southern England.



Amazon rainforest crosses a “tipping point” where extreme heat and

lower rainfall makes the forest unviable – much of it burns and is

replaced by desert and savannah.



Dissolved CO2 turns the oceans increasingly acidic, destroying

remaining coral reefs and wiping out many species of plankton which

are the basis of the marine food chain. Several metres of sea level

rise is now inevitable as the Greenland ice sheet disappears.



*3C-4C*

Glacier and snow-melt in the world’s mountain chains depletes

freshwater flows to downstream cities and agricultural land. Most

affected are California, Peru, Pakistan and China. Global food

production is under threat as key breadbaskets in Europe, Asia and the

United States suffer drought, and heatwaves outstrip the tolerance of

crops.



The Gulf Stream current declines significantly. Cooling in Europe is

unlikely due to global warming, but oceanic changes alter weather

patterns and lead to higher than average sea level rise in the eastern

US and UK.



*4C-5C*

Another tipping point sees massive amounts of methane – a potent

greenhouse gas – released by melting Siberian permafrost, further

boosting global warming. Much human habitation in southern Europe,

north Africa, the Middle East and other sub-tropical areas is rendered

unviable due to excessive heat and drought. The focus of civilisation

moves towards the poles, where temperatures remain cool enough for

crops, and rainfall – albeit with severe floods – persists. All sea

ice is gone from both poles; mountain glaciers are gone from the

Andes, Alps and Rockies.



*5C-6C*

Global average temperatures are now hotter than for 50m years. The

Arctic region sees temperatures rise much higher than average – up to

20C – meaning the entire Arctic is now ice-free all year round. Most

of the topics, sub-tropics and even lower mid-latitudes are too hot to

be inhabitable. Sea level rise is now sufficiently rapid that coastal

cities across the world are largely abandoned.



*6C and above*

Danger of “runaway warming”, perhaps spurred by release of oceanic

methane hydrates. Could the surface of the Earth become like Venus,

entirely uninhabitable? Most sea life is dead. Human refuges now

confined entirely to highland areas and the polar regions. Human

population is drastically reduced. Perhaps 90% of species become

extinct, rivalling the worst mass extinctions in the Earth’s 4.5

billion-year history.