THE possibility that, in an Obama administration, science will drive rational public policy provides an unprecedented opportunity to deal with a gnawing yet persistently neglected threat to the world: nuclear weapons.

No government is likely to declare how many strategic nuclear warheads it has, but the US and Russia are thought to possess at least 5000 apiece. The 2002 Strategic Offensive Reductions Treaty required each nation to have no more than 2200 "operationally deployed" strategic warheads by 2012, yet this represents no real progress towards disarmament, as the target number is essentially identical to that proposed at the 1997 summit on nuclear arms reduction between Bill Clinton and Boris Yeltsin in Helsinki, Finland.