National Grid has welcomed the government's decision to set tough new carbon emission targets, saying it gave the company "confidence" as it proceeds with a programme of investing ?16bn to upgrade the UK's energy infrastructure by 2015.  The business behind the pipes and pylons that carry gas and electricity around Britain said the overhaul is creating 5,500 jobs and it is devoting ?3.6bn to modernising the power network this year alone.  "It is a huge task to put in place the kind of changes we need to tackle the twin threats