Tuesday, August 19, 2008

Medium term climate forecasts – tell the truth & promote understanding

I recently posted on the foolish claims of Andrew Bolt that climate change had ceased in 1998. Among the points I made was that Bolt had used work of a certain German institute to back his claims when elementary care would have showed Bolt that, although this institute had argued that the rate of growth in warming might undergo a temporary slowing - the rate of increase was expected to resume and in no way rejected claims that long run climate was driven by atmospheric CO2 levels.

The distinction between medium term climatic trends and longer-term trends are beautifully discussed in the current NewScientist. The editorial to this issue argues that medium term climate forecasts – forecasts over the next 10 years or so - are a function of oceanic temperature oscillations whereas, yes, longer-term changes are driven by CO2 concentrations.

Short-term trends do suggest a future moderation in the rate of temperature increase but this implies nothing at all about longer-term temperature changes which are still inexorably forecast to continue to rise. NewScientist’s argument is that such short-term forecasts should be accurately reported even if sloppy commentators such as Andrew Bolt use this information to try to dispel the anthropogenic global warming hypothesis. Who could sensibly disagree? If temperatures do take a temporary dip this might create a slowing in impulses to manage climate but it is better to try to educate the public on the distinction between medium and long-term trends.

Long-term trends are driven by CO2 concentrations but medium term trends – whether the drought will continue to impact adversely on the Murray-Darling Basin – is a function of what is happening in the oceans. It takes a long time for the temperature of the oceans to change so the ability to predict what will happen iks not an impossibility. Most of the medium term climate on earth results from energy exchanges between oceans and atmosphere rather than overall changes in the temperature of the planet. The drought in Australia is then attributable to low water temperatures north ofr Australia and the expected duration of the drought can be understood by understanding these slowly involving temperatures.

I recommend the NewScientist article – a good read.


Francis Xavier Holden said...

The New Scientist article is onlu avaialble for subscibers.

I agree it was a good article - I read the magazine on Friday but left it up in Darwin.

jc said...


Seeing you’re appealing to higher authority let me do the same.

Dick Lindzen recently argued that the relationship between C02 and a warmer climate was much lower than what the models have been claiming.

Explain exactly why he’s wrong and why your “higher authority” is right.

Here he is:


Go to PDF doc 230 “Taking Greenhouse warming seriously”.

Really interested in your arguments.

Regarding your assertion that Australian climate in the southern parts has been affected by AGW, the CSIRO study that made the claim has basically been debunked. According to this research paper Australian drought seasons function in 30 to 40 years cycles and nothing at this stage suggests otherwise. Seeing the CSIRO hasn’t defended itself I would take this report to be the latest authoritive work on the subject.

Here is the link:


Notice he uses the CSIRO stats and throws them right back at their face.

Lindzen is particularly interesting as he asserts the models are simply too simplistic to be taken seriously, much less to base economic policy ……..that is about to direct 1% of GDP through a redistribution bonanza for big government types.

Lastly Harry, you ought to be really worried if I were you, as the government policy on AGW/ETS really looks to be a massive tax grab. A true believer in the science would be asking why the second best alterative nuke power isn’t in the policy mix and how do emissions fall.

derrida derider said...

Harry this is exactly why I have long argued that it is a serious tactical mistake for those seeking action on AGW to attribute the late drought to it, especially as we in fact don't know whether this particular drought had anything to do with AGW or not (we've no counterfactual).

Droughts form and break depending on much shorter term factors than AGW. That on average AGW makes droughts in SE Aust more common and severe doesn't tell us much about one particular severe drought.

To put it kindly, it would have been better if AGW activists had educated the public about the distinction between long-term AGW and medium-term ocean currents before those currents caused a pause in warming. Especially if we expected such a pause to occur. Instead we gave ourselves a credibility problem.

hc said...

DD, Your comments on the drought spot on. I must admit a certain amount of guilt in this area myself.

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