From Prof Jeffrey D. Sachs.

Sir, Regarding the news that the UK will host a Yemen terror summit: I recall a trip colleagues and I took to Yemen in 2005 at the invitation of President Ali Abdallah Saleh. The president conveyed to us the fragility of the social, economic and ecological situation, his ardent desire to speed economic development, and his request for international help to achieve the Millennium Development Goals. We toured impoverished areas in the countryside and in Sana'a, and learned first hand about the encroaching climate, ecological and hydrological crises. As usual, the aid agencies and multilateral organisations were utterly stolid in response, dribbling out minuscule help rather than facing up to the growing crisis.

Now, as in Afghanistan, Somalia, Ethiopia, Djibouti and other countries of the African and Asian dry lands, a neglected economic and ecological crisis is turning into a worsening security crisis. Washington is quick to spend on drones and troops, but almost immobilised in spending on development and environment. We are heading towards generalised violence across the Horn of Africa, the oil-poor Middle East, and the landlocked dry land regions of Asia, because we are unable to see the people there - with their hunger, water stress and lack of basic infrastructure and services - and only able to see the immediate threat to us. Until we treat others as human beings, not as objects of our security need, our insecurity is bound to grow.

Jeffrey D. Sachs,

Earth Institute,

Columbia University, US