life in a four degree world

From Climate Spectator today:

"Life in a four degree world

Giles Parkinson

The world has made a political commitment to limit the extent of global warming to 2?C, but the current path of emission trajectories ? and even the pledges made at the last climate change talks in Cancun ? will take the world well beyond that.

According to a report dubbed the ?Gigatonne Gap? prepared by the United Nations Environment Programme, the current commitments leaves a deficit of 5 gigatonnes to what the world aspires to achieve. Environmental groups believe that this scenario could lead to average global temperatures rises of 3.7?C or more.

What would this look like? The latest chapter of the update of the Garnaut Climate Change Review takes a peak into the future, arguing that understanding the global and local implications of 4?C and higher temperatures is crucial if the international community is to make informed choices about the balance between the ?extreme" rates of emissions reductions required to have a chance of avoiding dangerous climate change, and the "extreme" impacts and adaptation costs that are the alternative.

The report says research suggests that current global temperatures are near the highest levels reached in the Holocene period, and a global average temperature rise of 4?C from pre-industrial levels (or 3.5?C above 1990 levels) is well outside the relatively stable temperatures of the last 10,000 years that have provided the environmental context for the development of human civilisation.

?We would be in unknown territory for humanity,? Garnaut writes. ?The risks would be considerable.?

Under a global average of 4?C warming, there would be considerable regional variations. Parts of the Arctic could warm by 15?C, with large implications for sea levels and a range of bio-physical systems. An average temperature of 4?C above pre-industrial would give an 85 per cent probability of initiating large-scale melt of the Greenland ice sheet, put 48 per cent of species at risk of extinction, and put 90 per cent of coral reefs above critical limits for bleaching. It would trigger the lower threshold for initiating accelerated disintegration of the west Antarctic ice sheet and changes to the variability of the El Ni?o ? Southern Oscillation, and the upper threshold for terrestrial sinks such as the Amazon Rainforest, becoming sources of carbon rather than sinks.

?While these probabilities are lower than those under the no-mitigation scenario, it is unlikely that they would be considered acceptable by many members of the community, when, as in the 2008 Review, they are assessed against the likely costs of reducing them,? Garnaut writes.

?Severe weather events would intensify. Immense changes in the attractiveness of parts of the earth?s surface to support substantial populations would place great strain on national and global political systems. As we have discussed, recent science suggests that severe and catastrophic climate change outcomes may be triggered at lower temperatures than previously thought, further increasing the risks of catastrophic outcomes in a 4?C world.?

A four degree world was the focus of the "4?C Degrees and Beyond" conference in the UK in September 2009, and will be the focus of a July 2011 conference at the University of Melbourne. These events aim to concentrate minds on the costs of weakness in the global mitigation effort.

?The significant body of science looking at the probable climate impacts of climate change, and the risks that more dangerous outcomes will occur, suggests that the risks will increase immensely between 2?C and 3?C; even more for the difference between 3?C and 4?C, and further still for 4?C and 5?C, and again for 5?C and 6?C.

?There is no point in time at which it is wise to conclude that the damage already caused from climate change is so large that any subsequent damage is of minor importance.

?Moreover, beyond two or three degrees the challenges and costs of climate change associated with an additional degree of warming, regardless of the warming the planet has already experienced, are likely to overwhelm any attempts at adaptation to reduce the costs.?"

God will not be happy Technicals. We are the de facto custodians of the planet. I am quite serious.

http://www.climatespectator.com.au/commentary/life-four-degree-world