As the dust settles, the pledge will increasingly look like bad science, bad politics and bad faith:

• Unrealistic: G8 leaders appear cavalier with their maths: 50% is a nice, round number and 2050 gives the impression of long-term commitment. "Make no mistake, that's a lot," writes David Adam in The Guardian. He explains that developing countries will demand the right to pollute more for years to come, so the onus is upon rich countries -- the G8 itself. The UK alone could face up to 95% cuts in its carbon output within four decades to meet its share of the load. Yet many scientists argue that emissions cuts bigger than 50% are needed to offset potentially devastating climate change.
• No pressure: The reduction is just a goal, not a binding target, which would not have been accepted by either the United States or Canada, both of which are major energy producers and consumers.
• Base year? The worth of the G8's own agreement was called into question when Yasuo Fukuda, Japan's prime minister and the summit's chairman, appeared not to know the base year for calculating the agreed 50% reduction in carbon emissions. The Kyoto Protocol, which expires in 2012, used the base year of 1990, which at the time was seen as advantageous for the Europeans and difficult for the Japanese, who had already made energy efficiency gains in the 1990s. Just a few years makes a huge difference, writes The New Scientist. If the target were to cut emissions by 50% by 2050 relative to 2008 levels, that would mean a reduction of less than 40% when translated to 1990 levels.
• Interim milestones: Environmental campaigners say the communique has no reference to interim targets, such as ambitions for 2020, or 2030. Good scientists link long-term goals to short-term action to know if they are on track to succeed. As politicians usually work in five-year periods and act in five-year horizons, the absence of interim milestones is particularly surprising.

The G8's vague targets now seem like a fig leaf covering the lack of concrete long-term goals in UN-led talks that aim to create a new framework for when the Kyoto Protocol expires in 2012 (due to conclude in Copenhagen in December 2009). The eventual long-term goal, writes Adam, could be a 2C maximum temperature rise, or a 450ppm limit for CO2 in the atmosphere, or, at a push, a halving of global emissions by 2050. He adds that the acid test will be the United Nations Framework Convention on Climate Change (UNFCCC) meeting in Poland in December: "any more US stalling on a long-term target will expose the G8 statement as hot air."