Leaders of the world’s 20 top economies gather today in the US city of Pittsburgh to grapple with the aftermath of the worst global downturn in generations.Security concerns and that other problem when world leaders come to town – traffic snarlups – have meant a strong police presence as the city prepares to be the centre of world attention for two days. It is also an opportunity for interest groups to get their messages across. Pittsburgh once known as the “Steel City” has had to reinvent itself to prosper – an apt venue for the summit. As that is what has been happening to economies since the G20 last met in London. Central this time is the US plan to correct the world’s economic imbalances between big exporting countries and debt-laden nations. There is also the EU blueprint for a banking super-watchdog to regulate financial markets. But some say consensus on both is unlikely. David Smick – economic strategist said: “ I think they are arriving in Pittsburgh with kind of a self-satisfied smugness.It’s a you know, “we’ve brought the world economy and financial system back from the brink, but they haven’t dealt with the fundamental problem that got us into this difficulty in the first place. They’re approaching this summit with, -how can we avoid talking about the obvious so we can get out of town quickly and have a nice photo opportunity?” The other major issue is global warming. There has been little progress on how much industrial nations should contribute to helping developing nations cut their dependency on fossil fuel – a major cause of greenhouse gasses. Those negotiations will be closely followed by Greenpeace who are making sure climate change remains a top priority.