The stock response of many campaigners and activists to the sorts of headline announcements that emerge from G8 summits is that the devil is in the detail.

Whether the topic is development aid or climate change, their consistently wary advice is: "Read the small print". In the aftermath of the 2008 summit in Hokkaido, Japan, the reverse is true: for although the Japanese government hosts had sought to make climate change a central theme of the gathering, it is the lack of detail in the final summit statement on this issue that bedevils the G8 leaders' approach.

The media presentation might suggest otherwise - for since the meeting of the world's leading economies on 7-9 July came to a close, an army of headlines, features and opinion-pieces has been branded with the words "at least 50%" - the G8's agreed aim for cutting greenhouse gas emissions by 2050. In semantic terms, this is a step forward from the Heiligendamm, Germany summit communiqué in 2007, when the leaders said only that they would "seriously consider" such a target. True, words matter - but so does the thinking behind them. So while any movement that might ease and hasten United Nations negotiations on a new, global climate agreement is welcome, fixing on numerical emissions cuts without explaining their significance or how they can be achieved could prove unhelpful.

In this light, a closer look at the Hokkaido statement reveals three critical piece of missing information.

First, the G8 chose not to specify a baseline year and so left open the question "at least 50% of what?" In climate-change circles, 1990 is most often used as the yardstick against which cuts are judged, but US emissions have increased by 16% between then and now.

It is easy to see why the G8 left open this question - to get United States buy-in - but it renders their promise lame before it has even entered the race.

Second, the G8's emissions-reduction ambitions are global. What this implies is that the US and the European Union, China and India - and everywhere else, all the way to Burkina Faso - have (at a minimum) to halve their emissions by 2050. The leading countries of the global south who were invited to Hokkaido for talks - Brazil, China, India, Mexico and South Africa (the self-styled G5) - were, understandably, very quick to highlight this inequity. While much is said and written about rapidly rising emissions in these and other developing countries, they are still arriviste emitters. I

n historical terms it is the United States, Britain, and Germany that have done more than others to over-saturate the atmosphere with carbon. Even now, citizens of the EU emit twice per head than their Chinese neighbours and are many times wealthier.

Third, while a long-term target for cutting emissions is an important political reference-point, policy today would be influenced much more keenly by shorter-term targets. In 2007, the United Nations's climate experts challenged leaders of industrialised countries to set 2020 reduction targets of between 25% and 40% below 1990 levels. The G8 have not risen to this challenge.