IN THE theory of man-made climate change, two-thirds of the predicted warming comes from changes in humidity and clouds, and only one-third comes directly from the extra carbon dioxide (CO2) and other greenhouse gases.
The theory assumes humidity and clouds amplify the warming directly due to CO2 by a factor of three: extra CO2 warms the ocean surface, causing more evaporation and extra humidity. Water vapour, or humidity, is the main greenhouse gas, so this causes even more surface warming.
Not many people know that. It is the most important feature of the debate, and goes a long way to explaining why warmists and sceptics both insist they are right.
The warmists are correct that CO2 is a greenhouse gas and it causes warming, that CO2 levels have been rising, and that it has been warming.
Serious sceptics agree with all that, but point out that it does not prove that something else isn't causing most of the warming. By way of illustration, if the main cause of warming was actually Venusians with ray guns, then all those things would still be true.
The sceptic's main suspect is the sun. While the sun's radiation is roughly constant, its magnetic field varies considerably. This field shields the earth from cosmic rays that, according to recent experiments at the world's premier atom smasher CERN, might seed clouds. Clouds cool the planet, so if the sun's magnetic field wanes, then it might get cooler here on earth.
We scientists can calculate how much warming results directly from an increase in CO2 levels. We know how much CO2 levels and temperature have risen since pre-industrial times, but the warming directly due to CO2 is only a third of the observed warming. The theory assumes no other major influence on temperature changed, so the effect of the CO2 must have been amplified threefold, presumably by changes in the atmosphere due to humidity and clouds.
There is no observational evidence for this amplification, but it is nonetheless built into all the models. Sceptics point out that if the extra humidity simply forms extra clouds, then there would be no amplification.
If the CO2 theory of global warming is right, the climate models should predict the climate fairly well. If the CO2 theory is wrong, because there is another, larger driver of the temperature, then the climate models will perform indifferently.
According to the latest data from mankind's best and latest instruments, from impeccable sources, the climate models are doing poorly.
The first Intergovernmental Panel on Climate Change report in 1990 predicted air temperatures would increase by 0.30 degrees per decade, and by 0.20 degrees to 0.50 degrees per decade at the outside. But according to NASA satellites that measure almost the entire planet constantly, the trend since then has been 0.17 degrees per decade at most. The climate scientists ignore these awkward results and instead only quote temperatures from land thermometers, half of which are at airports where they are artificially warmed by jet engines and hot tarmac, while most of the rest are in warming micro-climates such as near air conditioner outlets, at sewage plants or in car parks. Obviously the data from these corrupted thermometers should not be used.
Ocean temperatures have only been measured properly since 2003 when the Argo program became operational. Some 3000 Argo buoys roam the oceans, measuring temperatures on each 10-day dive into the depths. Before Argo, we used sporadic sampling with buckets and diving darts along a few commercial shipping lanes. But these measurements have such massively high uncertainties as to be useless. Since Argo started, the ocean temperatures have been flat, no warming at all.
The assumed temperature amplification due to changes in humidity and clouds exhibits itself in all the models as prominent warming about 10 kilometres up over the tropics. We have been measuring the atmospheric warming pattern since the 1960s using weather balloons, released twice a day from 900 locations around the planet, many millions of them in total, and no such ''hot spot'' has been detected. This is direct observational proof that the amplification is missing.
The climate models predict that the outgoing radiation from the earth decreases in the weeks following a rise in the surface temperature, due to aggressive heat-trapping by extra humidity. But analysis of the outgoing radiation measured by NASA satellites for the last two decades shows the opposite occurs: the earth gives off more heat after the surface temperature rises. Again, this suggests that the amplification assumed in the models simply does not occur in reality.
Government climate scientists tend to excuse away these failings, often blaming unmeasured aerosols whose effects are only dimly understood. These excuses wear ever thinner as the CO2 level continues to rise but the temperature plateau of the last 12 years persists.
There are huge vested interests in the theory of man-made climate change. They will soon have to face up to the fact that they have been unwittingly relying on assumed amplification by humidity for most of the predicted temperature increases, and that the amplification is not there in reality.
Dr David M. W. Evans is a mathematician and engineer who consulted full-time for the Australian Greenhouse Office (now the Department of Climate Change) from 1999 to 2005. He says he changed from being a warmist to a sceptic after ''evidence supporting the idea that CO2 emissions were the main cause of global warming reversed itself from 1998 to 2006''.