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Here in Australia, one of the new senators, Malcolm Roberts, denies anthropogenic global warming. He and/or one of his staff plus a few other deniers have been busy posting odd things refuting AGW on his Facebook page, including various odd explanations and selective bits and pieces, old quotes, etc, to declare that AGW is all a hoax by scientists, scientific organisations and governments around the world. I’ve been picking the deniers to pieces over there but they don’t give up. I posted this comment on his video which he posted to his page a few days ago (although all I get in response is that I’m talking rubbish and more odd comments and selective quotes as the deniers continue to try and support their position) …

This video is misleading and gives totally the wrong impression. Carbon dioxide might be a small percentage of the atmosphere and man-made CO2 a smaller percentage still. But I think he’s mixing up his stocks and flows. He’s right in saying that man-made CO2 is only 3-4% of all CO2 but he seems to be saying that this is the level (stock) of man-made CO2 when in actual fact this is the percentage of man-made CO2 emissions (flow).

The problem is that only about two-fifths of this additional CO2 is absorbed and the rest stays in the atmosphere, building up steadily over time. Roberts seems to forget this. Before the industrial revolution, the CO2 absorption and release sides were pretty much in balance. Since then, we’ve had additional CO2 released by humans in ever-increasing volumes through all our various activities. It may seem small overall but, as I said, it builds steadily over time.

CO2 is now at about 400 parts per million or 0.04% of air as per the video. But over the last 400,000 years and up to the industrial revolution, CO2 varied between about 180 and 280 parts per million, in natural cycles. It was around the top of this cycle at the start of the industrial revolution and is now 40-45% higher at 400 ppm. Normally, it takes 5,000 to 20,000 years to increase by 100 ppm; this time, it has taken perhaps 150 years to increase by 120 ppm. The extra CO2 acts like a blanket, or a thicker blanket, enveloping the earth and keeps the heat in, thus the steadily increasing temperatures. This causes the ice the melt, sea levels to rise and an increase in wilder weather, with increasingly severe storms, larger tidal surges and more coastal flooding, causing damage and displacing people, often in the poorer parts of the world.

He then seems to compare Australia’s CO2 with the world’s total air. His subsequent statistics and analysis are therefore quite flawed.

I’m not sure where his carbon dioxide tax figures come up: $72 billion in five years. This was the estimated cost over this period of an American scheme in the 1990s. Emissions fell when we had carbon pricing in place, they rose before that and have risen again since. Also, getting rid of carbon pricing was estimated by the PBO to cost the budget $18 billion over four years, adding extra pressure to the budget. We now have the useless Direct Action policy.

Roberts says that temperature changes come first and then CO2 levels follow. It actually works both ways. In other words, changes in carbon levels both cause, and result from, changes in temperature. For example, when ocean temperatures rise, more CO2 is released into the atmosphere making the air warmer which means more CO2 is released. We have to also consider the rapid increase in temperatures this time around, much faster than historically. Graphing temperatures and CO2 levels since the 19th century, we can see a very high correlation over this period, which makes sense because the large increase in CO2 acts as a blanket keeping the heat in. To say that nature alone determines CO2 levels not humans, as Roberts states in the video, is simply wrong.

He doesn’t seem to offer any explanation for the increasing temperatures. It can’t be solar activity as that has fallen if anything since the 1970s, nor volcanic eruptions (these are low historically), nor Earth’s orbit (variations and effects on temperature are long term). That leaves greenhouse gases, which includes CO2 which causes up to a quarter of the greenhouse effect. Water vapour has a larger effect but it’s CO2 levels that have easily changed the most. Or does he think scientists use faulty thermometers, or are fudging the numbers?