Thursday, 23 October 2008
A reply to Bartek...
Bartek commented on one of my previous posts and suggested that weather patterns are not a good place to look for evidence of climate change as, firstly, our ability to measure the weather accurately was not as great 100 years ago and, secondly, one hundred years is not long enough to determine the true natural cycles of the earth's climate.
I should point out that Bartek and I travelled together in Morocco in August and, while I am serious about this subject, it should be read in a friendly tone.
Before I look at his two points, let me just step back a bit and take a broader view of the carbon cycle. Carbon is one of the 92 naturally occurring elements on the planet. We cannot make it and, excluding the odd rocket leaving the planet and the odd meteor entering, the amount of carbon on this planet is a constant.
It is found in three places:
1. The biomass - plants, insects, fish and animals.
2. Ground storage - oil, gas, coal and carbonate minerals.
3. The atmosphere - carbon dioxide.
The general trend of human occupation of this planet is to reduce biomass and consume the ground reserves. The carbon has to go somewhere, and that is to the atmosphere. Reafforestation and carbon sequestration are attempts to reverse this trend. Reafforestation is good but lags well behind still ongoing deforestation. Carbon sequestration sounds good in principle but I can't help having a sneaky suspicion that the carbon dioxide will leak out of what is effectively a hot rock sponge. We will see on that one but the catch is that it is an energy intensive process to capture, liquify and pump the carbon dioxide. Which produces carbon dioxide.
But the mass balance for the carbon cycle is irrefutable. The carbon has to be somewhere.
The question is: will it being in the atmosphere affect the climate?
It is easy enough, in the laboratory, to show that increasing the level of carbon dioxide in an enclosed atmosphere results in more absorbed infra-red radiation and subsequently raised temperatures. I should add that other gases contribute to the greenhouse effect, the most important of them being water vapour.
Water vapour is an important greenhouse gas? Yep. And if other gases, such as carbon dioxide, raise the atmospheric temperature you get more water in the atmosphere which raises the temperature further.
One of the problems that Melbourne has been having is that the humidity of the air has been too low for it to rain. Frustratingly, the clouds just drift past. Humidity is a function of temperature; raise the temperature of a gas and it will lower its relative humidity and it will hold much more water vapour.
To a chemist, all the chemistry and all the physics say that the process of global warming is a realistic one. The theory holds together.
As a gardener, I can agree that we are getting very little rain in Melbourne. As the friend of a farmer in central Victoria who has seen poor or failed crops for the last ten years I can tell you that the drought is having a devastating effect, financially, physically and mentally.
But is is really a drought? Or has the climate changed?
So, back to Bartek's issues:
Issue 1. Measurement techniques were flawed in the past.
Which measurements? My original post lamented the number of months when rainfall was below average. It is hard to get rainfall measurements wrong, if anything the old ones, if they were inaccurate, would be expected to be lower rather than higher, which only enhances my argument (and increases my lamentations). If they were randomly wrong then you would expect to see larger variation in the older data in charts like this:
The last ten years have been consistently below the median. The variation, visually at least as I can't be bothered doing the maths, seems fairly consistent 1855 - 1997.
Issue 2: That the natural changes in the climate are on much bigger cycles.
No doubt true. But that does not discount man-made additions to the cycles.
Melbourne's weather seems to have changes abruptly in 1997. I don't know why. If it was a natural cycle, I would expect a smoother change over a longer time.
That will do, I need to go and bucket water onto my vegetables.