by Peter Ballance 1 July 2009
Attention Prime Minister John Key
CLIMATE CHANGE / GLOBAL WARMING
Dear Mr. Key,
I understand that a country-wide series of meetings will be held to gauge public opinion on what New Zealands position should be in regard to the Copenhagen Climate Meeting Meeting.
As you are well aware, there is a great amount of noise surrounding the issue, but this email is to alert you to a single statistic the real signal that in my opinion as a scientist far outways all the others, but is given little attention especially by climate-change skeptics.
The primary driver of glacial-interglacial climatic cycles is the association of the three Milankovic astronomical cycles that in partnership, or in opposition, determine the amount of solar heat received at the earths surface. That is heat received, not emitted, from the sun. The other cycles like sunspots and regional oscillations, operating on time scales of years to centuries, merely add noise to the system. No other cycles, alone or in concert, trump Milankovic.
The Milankovic cycles are well understood, and can be both hindcast and forecast in terms of the quantum of solar heat per square metre that we receive (plus or minus the minor cycles). The figure varies around the earth, but is normally quoted for 65° North, that being the critical latitude for generation of ice sheets. Twenty thousand years ago, at the last glacial maximum (the Milankovic climatic minimum), 65N was receiving 365 watts per square metre. Ten thousand years ago, at the peak of the current interglacial (Milankovic maximum) 65N was receiving 480 w/sm. Now it is receiving 420 w/sm. It is clear that at this time we should be well down the slide to the next full glaciation, 80,000 years hence, in fact more than half way down.
It is a lumpy ride because of the interactions between the three cycles, but it is all downhill, each peak and each trough being lower than the one before.
The immediate question is why climate has been remarkably stable for 10,000 years, while the heat received from the sun has declined by 60% of its glacial-interglacial range. The pattern has been quite different from all previous glacial cycles. Clearly, a greater proportion of the suns heat is being retained in the atmosphere than in previous Milankovic cycles, and the only possible reason for that known to science lies in the quantity of greenhouse gases in the atmosphere. In previous cycles, greenhouse gases followed temperature changes. They didnt lead them, but did reinforce them. In this cycle greenhouse gas concentrations ceased to follow the Milankovic curve around 8,000 years ago, and have been rising steadily since then until the last 60 years when both they and temperature have begun to rise with increasing rapidity.
The conclusion is inescapable, Gentlemen human activity, both agricultural and industrial, has been driving global warming for 8,000 years, and the pace is increasing rapidly, along with population.
I trust that the Governments position at Copenhagen will reflect this central driving factor, and will not get bound up in the noise with which climate change skeptics and deniers try to derail clear discussion of climate change. Government scientists at NIWA and GNS will confirm the figures.