Tuesday, January 02, 2007

Up and down they go, where they stop, we can estimate with various levels of confidence...

I have been meaning to respond to David Duff and his 'hot air' for several months now, not least because of his remark that temperature records go 'up and down like a whore's drawers' [has to be quote of some day or other...].

But I was finally prompted to respond after I belatedly saw 'An Inconvenient Truth' (0r 'What Al Gore Did Next'). In the UK, the idea that human-induced climate change is happening is sufficiently uncontroversial that you forget that there are a whole heap of people over the pond for whom it isn't quite as clear-cut.

So let me lay it out straight. There is consensus within the mainstream of environmental scientists that climate change is happening. In addition, the balance of evidence is that climate warming over the last 50 years is primarily attributable to human activity.

Why do I think this? Well, I've read parts of the Intergovernmental Panel on Climate Change (IPCC)'s Third Assessment Report, published in 2001. A new IPCC report is due out early this year. The IPCC report is a consensus document laying out the current state of knowledge as agreed by academics working on climate monitoring and modelling, and related scientific questions. Since it is the 'agreed' current state of understanding, it is doubly conservative in its claims. Conservative because scientists try to draw conclusions only where they are supported by the available evidence rather than going off into unsubstantiated speculation. Doubly conservative because all these scientists have to agree.

The 2001 IPCC report states that:

There is new and stronger evidence that most of the warming observed over the last 50 years is attributable to human activities. Detection and attribution studies consistently find evidence for an anthropogenic signal in the climate record of the last 35 to 50 years.

Sceptics talking about cause-effect relationship between CO2 and temperature are getting confused about what is in contention

The important points are illustrated (sort of) in this diagram. This diagram shows a record of temperatures, atmospheric CO2 and methane concentrations for 400,000 years BP derived from an Antarctic ice core. Similar records can be obtained a variety of sources including trees.

CO2 and temperature broadly rise and fall together over the last 400,000 years BP. It is entirely correct to query a cause-effect relationship here. But there is a well known and entirely uncontroversial mechanism by which greenhouse gas concentrations change the Earth's temperature.

There is debate over the mechanisms through which greenhouse gas concentrations and temperatures interact together, specifically within the context of PREVIOUS INTERGLACIAL AND GLACIAL CYCLES. The trigger of previous glacial/interglacial cycles is the Milankovitch cycles but it is not known precisely how orbital oscillations translate themselves into glacial/interglacials through the Earth system. This is why understanding the relationship between the observed greenhouse gas and temperature rises is interesting for Quaternary scientists. It is, however, irrelevant to contemporary climate where we know that we are emitting greenhouse gases.

'Snowball Earth' is also irrelevant. Changes to the Earth's climate over time periods greater than 400,000 years are triggered by factors acting over geological timescales such as the breakup of continents and related changes in ocean circulation, etc.. These things are, again, not relevant to the contemporary climate change debate.

Given we are confident of the mechanism by which greenhouse gases lead to the retention of long-wave radiation in the Earth's atmosphere:

Sceptics talking about natural variability are also getting confused

The previous diagram shows that over the last 400,000 years, CO2 concentrations have rarely gone above 300 ppmv and certainly not above 325 ppmv. Current CO2 concentrations are 380 ppmv. This runs off the scale of the Antarctica ice core record shown in the IPCC report...

... Food for thought, me thinks. And it really is, well, that easy. It doesn't seem that easy because it requires a grasp of the science. And it's for this reason that Mr 'Dubya' Bush and co have managed to bamboozle and pull the wool over people's eyes.

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