Feature

Climate Of Opinion

Because of the greenhouse effect, banks are refusing mortgages on seafront properties and the carbon dioxide content of beer is under scrutiny. Is drastic action really necessary?

By John L. Daly

By now, nearly everyone is convinced that the Earth will soon heat up from the accumulation of greenhouse gases in the atmosphere. The strong media campaign by various interest groups has been so successful that many people are quite unaware that scientific opinion is actually divided on the issue, or that a counter-argument exists at all.

The greenhouse effect is an entirely natural phenomenon which prevents the Earth from freezing. Of the various gases involved, water vapour accounts for about two-thirds, while the much-maligned carbon dioxide (CO₂) represents only a quarter. Other minor gases, such as methane, ozone and nitrous oxide make up the remainder.

The key gas in the greenhouse debate is CO₂. This gas formed about 0.03% of the atmosphere 100 years ago, but its level has since risen to 0.035%, an increase of 25%. Carbon dioxide remains a trace gas and one that is essential for all life on Earth.

The crucial question is, if CO₂ were doubled from its current 0.03% level in the atmosphere to 0.06%, would the Earth tend to warm up? The answer is probably yes  but only by 0.25C. This should be seen in the context that the global mean temperature frequently fluctuates by as much as 0.5C or more in a single year, sometimes in a single month.

How, then, do the major general circulation models manage to predict temperature rises of more than ten times as much? They do so by juggling figures. Doubling the CO₂ is expected to produce a basic surface infrared back-radiation of 1.2 watts per square metre (W/m²). This will cause temperatures to rise by 0.25C only if all the energy is consumed in this manner.

Incorporated into the models is a series of positive feedback mechanisms, including increases in ocean evaporation, leading to more atmospheric water vapour, forcing temperatures even higher. As water vapour is a greenhouse gas, the temperature is assumed to increase to over three times the original CO₂ forcing, resulting in a rise of almost 1C.

That's just the start. Other positive feedbacks are added to the model to produce predicted rises of anywhere up to 5C, some 20 times the original CO2 forcing. In effect, the circulation models create a greenhouse mountain out of a CO₂ molehill.

Negative Feedbacks

What about negative feedbacks -- those mechanisms which act to reduce temperatures rather than increasing them? Such mechanisms abound in nature but are few and far between in the climate models. Among the most significant are reflection of sunlight from clouds and ice (the albedo effect) and the complex heat exchange mechanism operating between the oceans and the atmosphere.

For example, any slight warming would enhance ocean evaporation, as noted above, but it would also increase cloudiness, causing more light to be reflected away from the planet. This would tend to dampen the initial forcing, rather than exaggerating it. Neither of these crucial negative feedback mechanisms are modelled properly at all.

When attempts have been made to incorporate cooling mechanisms, the temperatures suggested by the models have taken a sharp drop. This became obvious in May 1989, when a NASA satellite experiment determined that the net effect of cloudiness was to cool the Earth rather than to warm it. The models (via their programmers) had mistakenly assumed that the warming greenhouse effect of clouds was more powerful than the cooling albedo effect. This startling news had considerable impact, causing most modellers to halve their predicted temperature rise.

A further problem with the computer models is their tendency towards chaos. Edward Lorentz, a US meteorologist, discovered that if he ran his weather model twice, it produced completely different weather patterns after a week of model time. That is, the model was highly sensitive to any changes in the initial conditions. The source of this chaotic behaviour is the use of millions of repetitive calculations which exaggerate the chaos inherent in the system.

Computer models make interesting research tools, but their temperature predictions should not be taken too seriously.

Do The Models Work?

One way to check the validity of a computer model of climate change is to set it with the climatic conditions of 100 years ago and then feed in the changes we know have taken place since then. We can then compare what the model says our present temperatures should be with what they really are.

This has been done. Various models predicted that the Earth should be 1.5C warmer than 100 years ago. It is not.

The 1988 Toronto Conference suggested an increase of 0.7C over that period; a study by the University of East Anglia estimated it at 0.5C. Both these estimates were derived from land-based temperature measurements, predominantly in urban areas and with a heavy northern hemisphere bias. Use of urban data has now been largely discredited for long-term climatic analysis because of the heat-island effect which distorts the readings.

A study by the Massachusetts Institute of Technology, using reliable ocean surface temperature data, suggested a rise of only 0.2C. Another estimate, by the US National Oceanographic and Atmospheric Administration, says that the United States has not warmed at all in the last 100 years. In May 1990, the US Department of Agriculture analysed 70 years of temperature data from 961 rural weather stations and found that the country had in fact cooled by 0.15C. A recent NASA satellite study spanning 1978 to 1989 shows that the 1980s have not experienced any warming trend at all.

The higher latitudes should have experienced even greater warming than the 1.5C predicted by the models, but there has been no warming trend detected. Temperature readings suggest that the Antarctic has been colder in the 1980s, with the coldest temperature yet measured on Earth recorded there in 1983: -89C.

A Hotter Sun

The models also assumed unchanging solar radiation, ignoring the fact that the Sun has been getting progressively hotter during the 20th century as a result of increasing intensity of the sunspot cycle. This solar activity will subside but, while it lasts, it can and does affect climate. If there has been a slight warming, as suggested by MIT's 0.2C estimate, this would be within the range expected from having a marginally hotter Sun.

So where is the 1.5C greenhouse warming predicted by the models? It's inside the artificial "imagination" of the models themselves. If these models cannot even model the recent past, they are patently useless as predictors of the future.

Some greenhouse theorists have suggested that all the missing heat is being stored in the oceans, to re-emerge at some time in the future. An MIT ocean temperature study has dismissed this. They found that ocean temperatures rose by 0.2C between 1860 and 1940, but have not increased at all since 1940.

The recent past indicates that the emphasis on positive feedbacks at the expense of negative ones has led to models which grossly exaggerate the potential global warming caused by CO₂. We are left with the original 0.25C rise, which could just as easily be countered by increased cloudiness or deeper tropical convection.

Thus the final temperature change could be as low as a tenth of a degree  hardly cause for hysteria.

Energy, Temperature Confused

Some greenhouse advocates claim that negative feedbacks can only result in a slightly less warm greenhouse, rather than a cold one. This conclusion is quite wrong as it confuses energy with temperature. Doubling the CO₂ content is expected to result in an increased surface energy flux of 1.2 W/m². If all this energy is consumed in evaporation, such as would happen in the tropical oceans, then the resulting additional cloudiness would add to the planetary albedo with no increase in surface temperature at all.

The greenhouse scare scenario assumes that radiation is the most important means of transporting heat from the surface to the upper atmosphere and eventually off into space. While this may be true for total heat transport, it is not necessarily true for slight marginal increases in surface energy flux.

Heat can be removed not only be radiation, but also by vertical convection, particularly deep tropical convection, and by latent heat removal through evaporation. In these latter mechanisms, the removed surface heat largely by-passes the greenhouse effect. Even where radiation is involved, the greenhouse gases do not absorb all infrared radiation. Large sections of the infrared spectrum are not subject to absorption at all, and so even radiation transport has gaping "windows" through which some heat can freely radiate to space.

Finally, are greenhouse promoters as objective and scientific as their approach would have us believe? One of the leading advocates of global warming is Dr Stephen Schneider, deputy director of the US National Center for Atmospheric Research. In 1971, he was warning the world of an imminent ice age, but dropped this when the post-war cooling bottomed out in 1976.

In an interview in October 1989 he said: "To capture the public imagination, we have to offer up some scary scenarios, make simplified dramatic statements and little mention of any doubts one might have."

Those doubts are there and they have to be addressed.

New Zealand's Greenhouse

The greenhouse effect has gained a great deal of attention in New Zealand, as elsewhere. Over a million dollars has been tagged for research into climate change; ministries, state-owned enterprises and private companies are producing a plethora of reports on the greenhouse effect and what it may mean for New Zealand's future.

In 1988, the New Zealand Climate Change Programme was established to assess the facts, examine the implications and make recommendations for responses. The Royal Society has developed two possible scenarios for climate and sea level in 2050, based on computer models and inference from geological and botanical records.

In the first scenario, New Zealand is predicted to be 1.5C warmer; prevailing winds 10% lighter; rainfall higher in the north; the snowline 100-300 metres higher and sea levels up by 20-40 centimetres. The second, warmer, scenario envisages temperatures 3C higher; stronger tropical cyclones in northern and eastern areas; rainfall decreases in Otago and Southland; snowlines 300-400 metres higher and sea levels up by 30-60 centimetres.

An apparent increase of 0.5C since the 1940s has so far had no measurable effect on snowlines, sea levels or rainfall.

The Ministry for the Environment has produced a 240-page report outlining the potential impact such changes would have on New Zealand, considering everything from fisheries and agriculture to tourism and transport. Reactions range from the mild to the extreme.

One bank in Christchurch is known to have refused a mortgage on a low-lying property because of concerns over rising sea levels. Breweries are being warned about carbon dioxide released from beer barrels. There are suggestions that genetic engineering of cow intestinal bacteria could reduce the amount of methane they produce.

The ministry warns that "we can't afford to wait for all the scientific arguments to be resolved before taking steps to resolve the problems".

John Daly is the author of "The Greenhouse Trap Why The Greenhouse Effect Will NOT End Life On Earth".