Reports of Earth’s demise are greatly exaggerated

Douglas Mackenzie (Letters, 26/6) claims that “for 800,000 years CO2 has varied in almost perfect lock-step with temperature”. His critical word is “almost”.

As he well knows the most accurate means of measurement of that period is ice-core data from Antarctica and Greenland which show that, for the multiple climate change events throughout that period, CO2 reversals always lagged behind the temperature change reversals by, on average, 800 years. It was temperature change driving the CO2 change, not vice versa, all to do with oceanic evaporation rates.

John Nethery, Chillagoe, Qld

I assure readers that despite Douglas Mackenzie’s alarmist claims there is no evidence that climate change from increasing CO2 levels could make Earth uninhabitable within the next 100 years.

Earth has been mostly much hotter than now and only about 12,000 years ago came out of an ice age, but life survived throughout.

As for the threat of CO2, since that last ice age, atmospheric levels were constant at about 280 parts per million until roughly 100 years ago when levels began to increase to today’s level of about 420 ppm. In that time, Earth was hotter than now 8000, 4000 and 2000 years ago and more recently colder at times — and all with constant CO2 levels.

Despite the recent 40 per cent increase in CO2 levels we are no hotter than in Roman times and sea levels, measured by tidal gauges, show no increase in Sydney Harbour and other places. Furthermore, climate is a chaotic system, which by definition defies prediction.

All we can say for sure about the next 100 years is that it will be hotter, colder or much the same as now. Anything else is soothsaying, not science.

Doug Hurst, Chapman, ACT

Douglas Mackenzie asserts that if carbon dioxide levels rise much above those of today, Earth will become uninhabitable. This ignores the geologically accepted fact that several million years ago, Earth’s carbon dioxide levels were of the order of a multiple of five of what they are now, and far from being uninhabitable, it saw the greatest explosion of life in its history.

Paul Yates, Beachmere, Qld

Large parts of Earth have always been uninhabitable but so say the end will be due to temperature rise caused by man-made carbon dioxide is unproven. In fact recent analyses of real data indicate the reverse.

Until some responsible body publishes quantified analyses of all possible causes of temperature rise, both natural and anthropogenic, together with all possible causes of climate change other than temperature rise, we shall continue to be assailed by extravagant claims of 100-year armageddon. They may be right but it could just as credibly be due to a series of massive volcanic eruptions and earthquakes, a large meteorite or an unprecedented attack of sunspots.

If carbon dioxide is the real cause of the problem, and Australia thinks it can make any more than token difference by going carbon free, then Peter Curlewis (Letters, 26/6) has the answer. Let the people express a view on nuclear power, without the input of pressure groups who cloud the issue.

Derek Fern, Box Hill, Vic

Douglas Mackenzie’s claims of CO2 being responsible for temperature rise is an exercise in cherrypicking and there is still no proof that CO2 is responsible. He should have pointed out that CO2 levels have followed not led temperature increases.

He may also ponder that for the past 10,000 years, with mostly stable CO2 levels, temperatures have generally been up to several degrees warmer — without man-made CO2. When raw figures are used we also see global temps falling from the mid-1940s to late 70s while CO2 was rising.

There are large bodies of scientific evidence that show the sun is the primary driver of global climate and that CO2 has minimal effect. We should look to science rather than alarmist claims in guiding our actions.

Chris Low, Coomera, Qld