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The scientific and public debate on what causes global warming has been very one-sided.
The claim the so-called greenhouse gases (chiefly the natural biological products, carbon dioxide, methane and nitrous oxide) are the cause of global warming is only a theory.
It is not fact or an unequivocal truth, even though the proponents of the theory would want to claim the science behind their theory is beyond debate and supported by an overwhelming majority of scientists.
The reality is the scientists associated with climate change groupings represent only a small proportion of the total physical and biological scientists around the world, but collectively they have had an inordinately large influence on governments and policy makers.
In addition, they have adopted a condescending tactic to rebut criticism by disparaging or questioning the integrity or knowledge of those who oppose their point of view by labelling them deniers and sceptics and to claim the majority of scientists accept the so-called science of greenhouse gas-induced global warming.
The fact is there has been no poll among scientists concerning their beliefs and a large body of physical and biological scientists do not accept this theory (a recent scientific publication rejecting this theory had 10,000 signatories), as they believe the historic scientific record shows clearly the sun has always controlled and continues to control global temperature, not greenhouse gases.
Put simply, although very complex in reality, the earth's temperature balance is dictated by the net effects of energy into (solar irradiance), and energy out of (back radiation and heat loss), the earth's atmosphere and surface.
If energy in exceeds energy out the earth warms and if energy in is less than out the earth cools.
The greenhouse gas theory claims that increasing greenhouse gases restricts thermal energy out to the point that the energy balance is positively affected and therefore the earth warms.
The greenhouse gas theory of global warming, however, is only a very recent proposition in earth time, relating to the period of time since the industrial revolution.
It does not explain the reasons for the earth warming and cooling during the millennia of its existence.
The alternative point of view held by a very large number of scientists is that the variation in energy received from the sun has a much greater effect on global temperature balance than the effect of greenhouse gases on energy loss and therefore it is the sun's activity that has always dominantly controlled global warming and cooling.
The scientific record shows clearly that over the past 3000 years there has been a more than 3degC change in global temperature, with both significant warming (in mediaeval times) and cooling (little ice age in 1700s) trends above and below present global temperatures.
What is important is these global temperature changes closely follow radiation level changes and indeed have the highest correlation with temperature change.
More importantly, since the end of the 1700s the earth has been in a general warming trend in response to increasing solar radiation.
And with this warming trend the scientific record shows that glaciers have been steadily retreating and sea levels rising for the past 200-250 years.
Thus it is important to realise these trends are not recent and started long before there was any significant burning of fossil fuels or increase in atmospheric CO2 levels.
However, the most damning evidence against greenhouse gas-induced global warming is the fact that there was a significant global cooling period between about 1940 and 1975 (associated with decreasing radiation levels) even though there was a three-fold increase in burning of fossil fuels and greenhouse gas emissions during this period.
This clearly demonstrates that global temperature was responding to changes in radiation levels and that rising levels of greenhouse gases were not causing global warming.
The recent continuation of the general warming trend in the past 30 years, which is the period upon which the greenhouse gas theorists exclusively concentrate, is associated with further increases in solar radiation level.
Of course, the greenhouse gas theorists claim this warming has been exclusively because of rising greenhouse gases during this period, but as the rates of glacier melting and sea rise continue as they have for the past 200 years, it can only be concluded that rising greenhouse gases are merely coincidental with the long-term warming trend, not the cause.
Niwa announced that the average temperature of New Zealand in 2009 was cooler than the long-term average (i.e. cooler than more than 50% of the 100-plus years since temperature measurement started), with some places between 0.5degC and 1degC lower than average; that there was record cold weather in the last northern hemisphere winter; and that the area of winter Arctic ice increased for a third consecutive year.
These are not coincidences.
While it is too early to be certain of a trend change to lower solar radiation and therefore lower global temperature, the fact that the approximately 11-year solar cycle reached its lowest level in more than 50 years in 2009 may represent the beginning of a new global cooling period despite higher levels of greenhouse gases.
If a second global cooling period occurs during a further period of increasing greenhouse gases, this will surely completely and finally discredit the theory of greenhouse gas-induced global warming.
The bottom line is that there is no unequivocal scientific evidence that global warming is caused by greenhouse gases.
And therefore, this means that the introduction of an emissions trading scheme (ETS) is useless in reducing global temperatures and represents only an expensive venture in futility.
The New Zealand Government would have been better off delaying the introduction of an ETS, as has the Australian Government, until the complexities of climate change are better understood.
Dr David Ivory is a Balclutha-based retired university teacher, scientist and senior United Nations staff member. His research interest has been in the general area of environmental (climatic) effects on biological processes.