Forecasting global climate change - Climate Change: The Facts - page 123

12 Forecasting global climate change
Kesten C. Green & J. Scott Armstrong
Warming by 2070, compared to 1980 to 1999, is projected to be … 2.2 to 5.0°C.
—CSIRO 1
By 2100, the average U.S. temperature is projected to increase by about 4°F to 11°F.
—US Environmental Protection Agency 2
Ifwedonotcutemissions,wefaceevenmoredevastatingconsequences,asuncheckedtheycould
raise global average temperature to 4°C or more above pre-industrial levels by the end of the
century. The shift to such a world could cause mass migrations of hundreds of millions of people
away from the worst-affected areas. That would lead to conflict and war.
—Nicholas Stern, Baron Stern of Brentford 3
Forecasts such as these are made by scientists and repeated by the political leaders they
advise. 4 TheprincipalsourceoftheforecastsistheUnitedNation'sIntergovernmentalPanel
on Climate Change (the IPCC). The IPCC's forecasts are the product of a collaboration of
scientists and computer modellers working for lobbyists, bureaucrats, and politicians. 5 The
forecasts of dangerous manmade global warming and its consequences are made with great
confidence, as are recommendations of actions to counter the forecasted danger.
History is replete with experts making confident forecasts. The record also shows that
the accuracy of such forecasts has been poor. Consider, for example, Professor Kenneth
Watt's forecast of a new Ice Age in his 1970 Earth Day speech at Swarthmore College:
Theworldhasbeenchillingsharplyforabouttwentyyears.Ifpresenttrendscontinue,theworldwillbeaboutfourdegrees
colder for the global mean temperature in 1990, but eleven degrees colder in the year 2000. This is about twice what it
would take to put us into an ice age.
Watt is not unusual among experts in making confident forecasts that turn out to be
wrong. Evidence from research on forecasting shows that an expert's confidence in making
forecasts about complex uncertain situations is unrelated to the accuracy of the forecast. 6
Those who believe that we can learn to avoid poor forecasts from history may wish to
consult the diverse examples in Cerf and Navasky's 1984 topic The Experts Speak . 7
We suggest that government policy makers and business managers consider whether the
IPCC's forecasting methods are valid before they consider making decisions on the basis