Humanity's lot is improving, but that of the world's poorest people is not. That is the conclusion of the latest "Human Development Report", published yesterday by the United Nations Development Programme. The report is a call to action, a plea for the world to help the millions who still have no access to clean water or decent sanitation and it must be answered. But it also shows how a great threat - global warming - could reverse the progress of recent decades.

Inadequate water and sanitation are a big cause of human suffering. Their effects are direct: 1.8m children die every year from diarrhoea and other diseases linked to hygiene. But there are indirect effects as well: tens of millions of women and children spend much of their day collecting water and miss out on employment and education as a result.