'In 1893 the World Columbian Exposition was held to celebrate the technological prowess of the time. (...). George Westinghouse, founder of Westinghouse and inventor of the modern compressed air train brake, wrote that trains were unlikely ever to go faster than 30 miles per hour. He saw this as no problem, however, because there was no need to go faster'.
With hindsight, it is of course easy to find such ridiculous predictions, in particular when they were issued by a single individual that could perhaps have drunk a beer too much before talking to a journalist. More interesting are forecast that were issued after a targeted brainstorming and not that long ago. The book Global 2000, written in 1980 as a sort of IPCC-like report to the President Carter contains many of predictions and scenarios, many of which are now, after only 30 years, not very accurate. Demography seems to be one of the fields with larger inertia and more tractable concerning long-term predictions. Nevertheless, Global 200 considered that the World population in 2030 would be 10 billion; in 2100 , 30 billion. These figures can be compared to the IPCC SRES scenario A2, the most pessimistic , which assumes 15 billions in 2100. The UN median scenario is today 9 billions in 2050, declining thereafter.
I stumbled by chance upon another set of predictions, this time for US energy consumption, all of the issued in the 70's with 2000 as time horizon. Some were more accurate than others, but there is clearly a bias.
From Craig et al., Can History teach us? A retrospective examination of long-term energy forecasts for the United States. Annu. Rev. Energy and Environment 27, 83(2002)
It seems that 'Be humble' is a good advice most of the time