Tim Curtin (Letters, July 31) quotes, as percentages, the rates of growth of annual net increases in the atmospheric concentration of carbon dioxide for the five decades 19602009.
Now, I'm no mathematician, but surely these numbers represent the third derivative in whatever function it is which relates concentration with time? The growth of annual increase would be the second derivative (acceleration) and the annual increase would be the first derivative (speed). The numbers show that we are still accelerating down the road of carbon dioxide concentration albeit with less pressure on the pedal. We started the journey at the 280ppm milepost around 1750 and have recently past the 380ppm mark travelling at about 1.8ppm/year. In the back seat, Economic kid is yelling to go faster, Industrial kid is looking out for speed cops and Political kid says she's going to be sick. Meanwhile Scientific kid is rummaging in the glove compartment looking for the map; he's pretty sure the road runs out at the 450ppm milepost and very sure that the brakes should be applied now.
As a passenger, trapped in the boot, I'm not happy.
Nick Ware, O'Connor
Evidence provided
Aert Driessen (Letters, August 1) asks for evidence that global warming is accelerating. Firstly, what does the word ''climate'' mean? It means the long-term average of the weather, generally defined to be over periods of 30 years or more. Temperatures have a lot of short term variability: they bounce up and down from year to year. The important aspect is the long term trend. Taking the most commonly cited data for global temperature, from the Hadley Meteorological Centre in the UK, the picture is clear. Annual averages, dominated by short term variability (the ''weather''), bounce up and down all the time, but 30-year averages, showing the underlying trend (the ''climate''), have been rising since early in the 20th century, and especially since about 1975.
Specifically, the 30-year average shows a warming rate of 0.88 degrees per century in 1989, a rate of 1.10 degrees per century in 1999, and a warming rate of 1.52 degrees per century in 2009.
Looks like acceleration to me.
Matt Andrews, Aranda
Check for yourself
Mark Diesendorf quite correctly states that ''global climate change is accelerating''.
This is queried by Aert Driessen, who asks for evidence. Driessen does add that ''nothing in science is certain'' a message which his fellow denialists might take on board.
However, the climate research bodies around the world (Hadley, Scripps, NOAA, NASA, CSIRO, the universities) and the bulk of the world's climate scientists, including noted Australian researchers such as Professor Will Steffen, Dr Graeme Pearman, Dr Barry Brook, Professor Matt England, Dr Mike Raupach, to name just a few, endorse the warnings of the IPCC: that human activities have added to natural atmospheric CO2, and that this has changed the world's climate in the past century.
The recent Synthesis Report of June 2009, see http://lyceum.anu.edu.au/wp-conte nt/blogs/3/uploads//Synthesis%20R eport%20Web.pdf emphasises that climate change is ''tracking the worst case scenarios''. All these scientists could possibly be wrong. As Driessen says, nothing in science is certain. All the data from satellites, balloons, ocean temperatures, ice-cores and so on could improbably have been misinterpreted.
But the scientific evidence is mounting every day that global climate change is real, is happening now, and will have massive consequences.
Check the science for yourself.
Nick Goldie, Michelago, NSW
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