Countries are issuing, or at least preparing, a long list of promises to help finance research into new seeds, build irrigation canals and spread fertiliser use among small farmers (seeds, irrigation and fertilisers were the main components of the first green revolution in the 1960s).

ECONOMIST: The world food summit

Purves is very concerned about the glaciers in the Himalayan mountains that are the main source of water for irrigation and drinking in China and India, well over 2 billion people.

FORBES: 500 Million People Will Be Displaced By Glaciers Melting In Greenland And The Himalayas

The outlook for the winter wheat crop is also poor, with India's main reservoirs, a source for irrigation canals, one-third below their seasonal average.

ECONOMIST: India's water crisis

Of greatest concern initially, the Keystone XL pipeline was designed to run through Nebraska's Sandhills, which lie above the Ogallala Aquifer, the main source of drinking water and irrigation for millions of people.

CNN: STORY HIGHLIGHTS

The damage will be felt only in the longer term, since the main effect may be to delay the start of big infrastructure projects, from roads to irrigation schemes.

ECONOMIST: Thailand