Keith Hunter’s statement asserts: The evidence pointing towards AGW comes from multiple independent lines of argument, each pointing in the same direction. … a few examples follow.
This is his first example:
It is a plain fact that human activities have significantly increased the concentrations of greenhouse active gases in the atmosphere, particularly since the mid-20th century.
Who will tell him that nothing could be further from plain? What does he mean by “greenhouse active gases”? Does he mean that water vapour has increased in the atmosphere? Does he include methane? Nitrous oxide? Or does he only mean carbon dioxide?
Does he exclude the possibility that increased temperature has driven more carbon dioxide from the oceans into the atmosphere?
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This is a “plain fact” in the same way that the Royal Society’s take on the mathematics of global warming is “simple physics”.
The paper surely can’t mean that water vapour is an inactive greenhouse gas. But as the bulk of Professor Hunter’s AGW “evidence” is focused on fossil fuels, he probably means this statement to be limited to carbon dioxide. Even then, it is not immediately obvious that an increase from 0.022% to 0.028% should be described as “significant”.
The greenhouse gases of greatest concern to New Zealand are methane and nitrous oxide. The concentration of atmospheric methane raced upwards in the eighteenth century, then plateaued during the huge population increases of the nineteenth and twentieth centuries. It spiked upwards in the 1990s and then went flat for a decade. There is no reason to assume any of these gyrations had anything to do with human activities.