It’s all very well doing what alarmists do which is to say that Co2 is rising and temperatures are rising so in the absence of any other known cause it must be man made CO2 that is warming the planet. That approach ignores both the differing scale of the possible influencing factors and the clear historical relationship between cooler climates and periods of a less active sun. The presence of the sun must be a much bigger influence on global temperatures than the greenhouse characteristics of CO2 on it’s own.

At most the greenhouse effect can only be marginal though some have tried to talk it up by asserting that the planet would be very much colder without a greenhouse effect, which is correct, but avoids the issue of the rather small proportion of the overall greenhouse effect provided by CO2 and the even smaller proportion provided by man. It also begs the question as to whether the oceans are slowly releasing CO2 as a result of natural warming. If the oceans warm for any reason they will release CO2 into the atmosphere because water holds less CO2 at higher temperatures.

The greenhouse effect, as a whole, may smooth out rises and falls in temperature from other causes but is not itself the determining factor for global temperature. If the heat from the sun declines the global temperature will fall with or without any greenhouse effect and if the heat from the sun increases the global temperature will, of course, rise. The greenhouse effect does not create new heat. All it does is increase the residence time of heat in the atmosphere.

In the ice core record, CO2 increase has always lagged behind temperature rises and the lag involved is estimated to be 400 to 800 years. There has never been a period when a CO2 rise has preceded global warming. I have seen it argued that the past 30 years has been so exceptional that it MUST, for the first time in the history of the globe, be CO2 driving the warming trend. That is an assertion of such low probability that it should require very powerful evidence to support it. I have seen no such evidence. Indeed, on a cursory inspection the slow but steady increase in atmospheric CO2 is clearly not coming through in a slow but steady rise in global temperatures. Instead we see rises and falls in global temperatures that bear no obvious relationship to the steady rise in CO2 unless one puts the cart before the horse and announces that there is no other possible reason and the trend period adopted is carefully chosen to suit the proposition.

All it needs to cast doubt on the CO2 theory is an alternative possibility to explain a rising global temperature trend over the past 500 years and there is one. Everyone will have heard of the Little Ice Age and the global temperature would appear to have been recovering from it ever since. On a balance of probability is that not the more likely explanation of an overall warming trend ever since? Why introduce manmade CO2 at all except for politically motivated reasons? By all means exclude a recovery from the Little Ice Age as the reason if one can but the burden of proof is heavy and probably impossible to discharge with current knowledge. There was also a Mediaeval Warm Period (MWP) that preceded it. It has been asserted by some that the MWP was not as warm as the planet is now but there is evidence to the contrary such as Viking settlements in Greenland at the time. It has also been asserted that the MWP was not worldwide but some recent indications have been found in South America that it was warm there at about the same time. In any event it is unlikely that such a warm period affecting Greenland and Western Europe would not be worldwide. The heavy burden of proof is on those who would seek to deny it.

Be that as it may, there is a probability rather than a possibility that the warming trend since the lowest point of the Little Ice Age is continuing to this day and is the real cause of recent observed warming with only a minimal contribution, if any, from man made CO2 emissions.

Then there is the matter of scale. The greenhouse effect is mainly a phenomenon of the land surface and the atmosphere because more of the incoming heat is absorbed by water as compared to land and a lower proportion is reflected to participate in the greenhouse effect. However the surface of Earth is 70 % water. Water has a hugely greater heat carrying capacity than the land or the atmosphere above it. Land loses most of the heat it receives during the day via overnight radiation and the atmosphere loses heat rapidly via convection, rainfall and radiation to space despite the greenhouse effect. The true heat store that we need to consider, dwarfing by far any atmospheric greenhouse effect is all that water. I describe the implications of that below.

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