On the other side of the pond, the European Union (EU) agreed a 10% minimum target for biofuel use in transport by 2020. That deal is part of a new European commitment to cutting carbon dioxide emissions by 20% from 1990 levels by 2020. What's more draft climate change legislation just announced in the UK could tie the nation into cuts of a hefty 60% in carbon dioxide emissions by 2050.

And that's a key difference between the US and EU approaches. In a situation that has uncanny parallels with the Kyoto Protocol - where Europe has committed to targets (albeit the slightly smaller average 5% cut in emissions over 1990 levels by 2008-2012) but the US has refused to ratify the convention - Europe has again committed to actual greenhouse gas cuts while the US has not.

The distinction is particularly important in an area such as biofuels where reductions in carbon dioxide emissions do not automatically follow an increase in biofuel consumption.

Take the case of ethanol, currently produced from corn in the US and sugarcane in Brazil. Although the combustion of ethanol produced from these crops is carbon neutral on a broad scale, as the plants have absorbed during their lifetime all the carbon dioxide subsequently released when their byproducts are burnt, other emissions-releasing factors come into play. For example, growth of crops under intensive use of industrial fertilizers, fossil fuel consumption during the conversion of the crop to ethanol, and transport associated with intensive agriculture and crop processing can all add to the greenhouse gas emissions total.

In contrast, the second generation biofuels currently under investigation, such as ethanol created from cellulosic sources - woody plants like switchgrass or poplar rather than corn or sugarcane - have the potential to cut greenhouse gas emissions by 90% or more when replacing gasoline. That's because the ethanol conversion process burns part of the plant, rather than fossil fuels, to provide the heat needed for fermentation. But such technologies are not yet in widespread commercial use, although there's extensive research underway.

Of course, greenhouse gas emissions are not the only issue that could arise alongside a massive boost in biofuels uptake. There may also be increases in food prices due to competition for agricultural land - corn prices have already risen in Mexico, which is a net importer of corn from the US - and potential changes in land use, including deforestation, to grow more crops for biofuels.

That said, President Lula claims Brazil has shown that it is possible to increase production of biofuels without harming the production of food and also reducing deforestation of the Amazon region. Indonesia, meanwhile, has announced that it will not permit or license palm oil plantations for biodiesel production in national parks or protected areas.

It appears, so far, that the US is ramping up its biofuels goal with more of a view to energy security issues than climate change. In a speech during his recent trip to Brazil, Bush placed environmental stewardship third in his list of reasons for diversifying energy supply, after the national security issue of being dependent on oil from overseas and the economic problem of oil dependency. And that would certainly seem to be true if the focus is on increasing use of ethanol produced from corn.

While individual US states and cities - notably California - are making commitments on greenhouse gases, the situation needs addressing with a firm target on a national level. Indeed, this is what recent industry coalition the US Climate Action Partnership has called for.

As the EU is expected to raise its commitment for emissions cuts from 20% to 30% of 1990 levels by 2020 should nations such as the US, China and India also sign up to reduction targets, it's even more imperative that the US commits to greenhouse gas cuts rather than promoting measures such as biofuels and solar energy on a piecemeal basis. As European Commission president Jose Manuel Barroso said, "We can say to the rest of the world, Europe is taking the lead, you should join us in fighting climate change."