It was well said recently by Bob Brockie, in one of his excellent articles in the "Dominion Post" that "Forecasting is difficult, particularly about the future"
Economics is not an exact science, and the least exact of all are its forecasts. It was stated at a conference I attended recently that the only job where you are still employed even when you are always wrong is "economist"
Although economic theory is influenced by fashion and by politics, we still need economic forecasts. Most professional economists know that their forecasts cannot be of much use beyond a few years because changes in technology and social structure are very difficult to predict. I have a paper published by one of the international teams, IAASA, who surveyed their past forecasts and found that the lowest one was always the most successful. Yet politicians and the public always prefer the highest one.
I have developed a great respect for the second Governor of New Zealand, Robert Fitzroy. He it was who, as the very young captain of the "Beagle", chose Charles Darwin as his travelling companion on his epoch-making voyage around the world in 1831-36. Between them they founded the science of evolution, even though Fitzroy rejected it. He became Governor of New Zealand in 1841 at a time when several of his "Beagle" shipmates, including the captain of the "Tory", Edward Chaffers, had reversed British Government policy against settlers. Fitzroy succeeded the first Governor, Hobson, in 1843, only to be ejected by the settlers in 1845 because he was too sympathetic to Maori and believed that they should be helped, not exploited. His little book on New Zealand is still well worth reading.
Back in Britain he was promoted Admiral and was the first Head of the British Meteorological Office. He invented a barometer and he invented the Weather Forecast. As an old salt, he worried most about the prediction of storms at sea which caused great loss of life in the days of sailing ships. He wrote letters to all of his shipmate friends and compiled a database of the possible indications of a forthcoming storm from which he issued regular storm warnings. He was, to begin with, often wrong, and the public criticism of his work, to which he devoted long hours, led to his suicide in 1865 at the age of 60, by the same means taken by his uncle, Viscount Castlereagh, former British Foreign Secretary some years before.
His methods are essentially unchanged today. The database is huge. It has the benefit of a network of observations and past records of many climate factors, and nowadays a battery of computer models. All the same, they still use the same technique of doing their best to combine these into the hourly, daily, weekly and monthly forecasts with which we are so familiar. It is never certain. It is perhaps slightly better than the days when you got a better result by forecasting that tomorrow will be identical to today, but not all that much. It gets worse the further forwards you try. But still they keep on using existing and past information to try and improve the next forecast. We have come to depend on it.
Computer climate forecasts are different. They are based on a presumed theoretical understanding of the climate. They prefer forecasting so far ahead, usually 100 years, that they can be sure nobody can check up on theme, and, perhaps more important, they do not and do not need to check up on themselves.
Computer models are widely used in industry. No honest scientist or engineer would dream of using one for a practical forecast unless they had been "validated". The only way you can validate a computer model is to prove that it is capable of reliable forecasting of a range of situations for which it is to be used. The level of accuracy can then be determined.
No computer model of the climate has ever been validated so the level of accuracy is unknown.. My greatest success as a commentator of drafts of IPCC Reports is with the 1995 Report where one Chapter in the Draft was headed "Validation of Climate Models". I pointed out that since no model had ever been validated the title should be changed. They actually changed the title, and the word "validation" in the text, no less than fifty times, and they forbid the use of the word ever since. They also forbid the use of the word "forecast", which has to be replaced with "projection", where it is pointed out that each "projection" depends on the assumptions made. This reservation is not often made by politicians, or journalists.
They do not even attempt to "validate" models, and sometimes claim that it does not matter if they fail over the short term, because they only apply to the distant future.
They do, however, "evaluate" models, and they do this by trying to fit them to selected climate sequences. Since most of the "parameters" and equations used in models are highly uncertain, it is often possible to fit their model to some climate sequences, if carefully chosen. We used to call this "fudging". In the latest one they claim they have successfully simulated the past surface temperature record, but they do not tell you that they left out a few factors which won't fit, like the recent El Niño ocean events
None of the models has successfully predicted any future climate behaviour. On the contrary, they have always been wrong. My paper, "The IPCC future projections are they plausible" Climate Research 1998 Vol 10 pages 155-162 shows that all of the forecasts put forward by the IPCC in "Climate Change 1995", purportedly beginning in 1990 were exaggerated compared with what was actually happening in the climate.
In my book "The Greenhouse Delusion; A Critique of 'Climate Change 2001" I showed that all of the revised "projections" in that IPCC report even took an exaggerated starting point in the year 2000, and, as before, all exaggerated what was actually happening.
The new IPCC Report "Climate Change 2007" continues to use these discredited "projections" None of them can explain why global temperatures have not increased for 8 years, or that atmospheric methane concentrations are falling, not rising.
Yet environmental activists like Al Gore and Sir Nicholas Stern have chosen the most extreme "projections" as "forecasts".
The Report is about to be launched by the IPCC on Friday this week. If you actually read the report, or even the newspaper summaries that are now appearing, you will find that it is almost exclusively based on these unreliable and untested "projections" and has little to say about the real causes of changes in the climate.