Clear signs of trouble are emerging in the US, until now the last bastion of strength. The New York Institute of Supply Management said its ISM business index – a proxy for business demand – flashed a "screeching halt" in May, crashing to 49.9 from 61.2 in April, where anything below 50 denotes contraction. Unemployment is rising again after grim jobs data for April and May, indicating that the economy may have fallen below stall speed.