Global heating & IPPC 4

I’ve been trying to get my head around the Intergovernment Panel on Climate Change (IPCC) report ‘Climate Change 2007: The Physical Science Basis – Summary for Policymakers’ document. Among the better commentaries I saw were the New York Times and a good summary in The Australian. Warming is definitely occurring and, with probability = 0.9, it is anthropogenic. The warming will continue for centuries but its worst effects can be dealt with by reducing emissions – though the IPCC are not concerned here with policy.

Labor’s Kevin Rudd made yet another of his ‘fork in the road’ pronouncements and engaged in petty politics. Give us a break Kevvie. I find it hard to take the Labor Party seriously on the climate change problem given that they rule out the nuclear option. Howard returned Rudd’s fire by pointing out this obvious anomaly.

In the local blogosphere Tim Lambert at Deltoid seemed more interested in covering up a forecasting error he made than in discussing the report. John Quiggin was concerned with oil industry attempt to fund research that criticized the report. Andrew Norton makes a pretty good post on the topic – he criticizes John’s critique as ‘McCarthyism’.

But in all these commentaries there is not actually a lot on the substance of the report itself. It is an interesting document and rather complex. Some risks such as melting of the polar icecaps are downplayed. Patrick Michaels at the Cato Institute draws optimistic conclusions from the report's empirical findings. Our understanding of global warming will evolve and policy responses need to be a rolling plan.

Summary effects (based on Reuters):

1. Temperature rises. The range of possible temperature increases this century has increased to 1.1-6.4 degrees Celsius in this report from 1.8-5.4 degrees in the IPCC's previous report in 2001. Note the lower minimum anticipated increase.

The projected temperature increase to 2100 has risen because it is now considered that global warming will make nature less able to absorb carbon dioxide.

This alone could raise estimates by more than 1 degree this century.

For the first time the IPCC gives ‘best estimates’, giving greater certainty than predictions in earlier reports. The best estimates range is for a 1.8-4.0 degrees temperature rise by 2100. Only one of the six scenarios analysed generated a best estimate of less than 2 degrees warming this century (1.8 degrees).

The report does not include the possible warming impact of methane, a potent greenhouse gas, escaping from melting permafrost – there isn’t enough evidence.

It is ‘very likely’ that extremes such as heatwaves and heavy rains will become more frequent.
Warming is expected to be greatest over land and at high northern latitudes and least over the Southern Ocean and North Atlantic.

2. Sea level rises. The report cites 6 models with core projections of sea level rises ranging from 18-59 cm this century. That is a narrower and lower band than the 9-88 cm gain forecast in 2001. Note the lower anticipated maximum increase - this is the subject of Lambert dispute mentioned above.

If the Greenland ice sheet melts in the future proportionally to the temperature rises then sea levels would rise by up to 79 cm, not 59 cm, this century. Some models show an ice-free Arctic in summer by 2100 (meaning that sea ice floating in the water disappears, but not ice resting on Greenland).

If the Greenland ice sheet melted completely that would lead to a 7 metre sea level rise but this would occur only with a sustained temperature increase over 3 degrees for millennia Jurgen Willebrand, the report's author with special expertise in ocean effects, told Reuters. Thus trends are serious but somewhat less serious than earlier apocolyptic views.

3. Ocean currents. The report predicts a gradual slow-down this century in ocean currents such as the one which carries warm water to north-west Europe. Again less drama than in soime earlier forecasts.

‘It's very unlikely there will be an abrupt breakdown in ocean currents in the 21st century,’ said Willebrand.

‘Most models predict a gradual slowdown this century but you shouldn't expect a fall in temperatures (in Europe), because global warming is happening.’

4. Hurricanes. The report says it is ‘more likely than not’ that a trend of increasing intense tropical cyclones and hurricanes has a human cause. It expects such tropical cyclones to become more intense in the future’.

There may not be an increase in number, there may be a re-distribution to more intense events - which is what has been observed in the Atlantic since 1970’ lead author Stott told Reuters.

I’ll try to add further good posts if I discover them and welcome reader's advice.