GENEVA (Reuters) – Climate change has made history  an inaccurate guide for farmers as well as energy investors who  must rely on probabilities and scenarios to make decisions, the  head of a United Nations agency said yesterday.

Michel Jarraud, director-general of the World Meteorological  Organisation, said that water and temperature projections have  become more valuable than the historical weather data that long  governed strategy in agriculture, hydro-electric power, solar  technology and other fields.

“The past is no longer a good indicator of the future,” the  WMO chief told a press briefing, describing climate modelling  and prediction as key to fisheries, forestry, transport and  tourism, as well as efforts to fight diseases such as malaria.

People looking to build energy infrastructure are especially  hungry for specific environmental information that can affect  the long-term profitability of their projects, he argued.

“If in 100 years there is not going to be water going into  the dam, it’s not a brilliant investment,” Jarraud said.

In the farming sector, the Frenchman suggested that guidance  passed down through generations about how to prepare and manage  crops was becoming less relevant because of changing patterns of  heat, humidity and water access around the world.

“This traditional knowledge is no longer adapted. It’s exactly because your grandfather did this that you shouldn’t do it, because the context has changed,” he said.

“This is something completely new — to make decisions not  on facts or statistics about the past, but on the probabilities  for the future,” he said.

About 1,500 policy-makers, researchers and corporate leaders  will meet next week in Geneva to seek to improve the way climate  information is collected and shared, among governments and also  with the private sector.

That Aug. 31 to Sept. 4 meeting, which will take the pulse  of countries who will seek in December to clinch a new global  climate pact, is due to include top UN officials including  Secretary-General Ban Ki-moon and 80 ministers and 20 heads of  state or government, mainly from the developing world.