The President of the United States, Barack Obama, delivered an impressive and impassioned speech on climate change on 25 June at Georgetown University in Washington DC.
It followed earlier promises to make the issue more prominent during his second term in office. In his State of the Union address in February, President Obama declared "for the sake of our children and our future, we must do more to combat climate change", and warned "if Congress won't act soon to protect future generations, I will".
So ahead of the speech on 25 June, the White House published 'The President's Climate Action Plan', listing measures that would be taken without the need for further federal legislation. These included a 'Presidential Memorandum' instructing the Environmental Protection Agency to engage individual States about new regulations limiting the amount of carbon dioxide that can be emitted by power station. This is likely to lead to the phasing out of coal as a source of electricity unless it is burned with carbon capture and storage technology.
While President Obama's personal leadership on climate change is extremely welcome, the measures he outlined are simply not sufficient given the scale of his ambition. Without Congressional support for new federal legislation to reduce his nation's emissions, President Obama is trying to fight climate change with one hand tied behind his back.
Emissions of greenhouse gases by the United States in 2011, the most recent year for which figures are available, were 6.7 billion tonnes of carbon-dioxide-equivalent. This was below the peak of 7.3 billion tonnes in 2007 and 6.9 per cent lower than in 2005. The Obama administration pledged at the United Nations climate change summit in Cancún, Mexico, in December 2010 that the United States would reduce its emissions by 17 per cent by 2020 compared with 2005.
Most of the reduction in emissions has been achieved somewhat unintentionally by a reduction in economic activity and the exploitation of domestic shale gas reserves, which has lowered the price of natural gas as a fuel source for power generation. This natural gas has displaced coal, which generates twice as much carbon dioxide per unit of electricity.
In 2012, carbon dioxide emissions from energy use in the United States fell by 3.9 per cent compared with the previous year, although the Energy Information Administration expects them to rise again over the next two years.
More significantly, emissions of greenhouse gases by the United States in 2011 were 8.4 per cent above their 1990 level, which is used by many countries as the most appropriate baseline. As the population of the United States was 311.6 million in 2011, per capita emissions were about 21.5 tonnes. To have a reasonable chance of avoiding dangerous global warming of more than 2 centigrade degrees, average per capita emissions across the world will have to be cut to just 2 tonnes by 2050.
So the United States needs to do much more to reduce its emissions, and it will require stronger action at federal level to match the considerable action that is already being undertaken by individual States, cities and companies.
The main obstacle to progress is the Republican Party which has forced itself into an ideological straitjacket of climate change denial that prevents even its moderate lawmakers from publicly acknowledging the strength of scientific evidence.
Responding to President Obama's initiative on climate change, the Speaker of the House of Representatives, John Boehner, chose only to highlight how reducing emissions might affect coal companies. This follows comments to the newspaper 'USA Today' last November in which Mr Boehner accepted that the climate is changing but claimed "what has initiated it, though, has sparked a debate that's gone on now for the last 10 years".
This is despite the unanimous verdict of all of the leading scientific organisations in the United States, including the National Academy of Sciences, that global warming is being driven by human activities, primarily emissions of greenhouse gases.
Mr Obama must continue to take his case for action to the American people and to challenge Congress to back his ambitions.
Bob Ward is policy and communications director at the Grantham Research Institute on Climate Change and the Environment at London School of Economics and Political Science.