Green bond fans point to Massachusetts as a prime example of a boost in investor appetite for bonds once deemed risky and experimental. The US state had to scale back a $1.1bn bond by about 40% on June 4 as investors backed away but its $100m “green” tranche was a third oversubscribed and issued without a hitch. A small tranche, but a small victory for green bond advocates.

Massachusetts issued the green tranche to exclusively finance clean water, energy conservation, open space and other environmental infrastructure projects.