The recession and inadequate project preparation have led to almost 30 per cent of projects under the United Nations' carbon trading system failing to deliver any credits, according to a new report.

Projects to prevent emissions from waste, such as landfill gas capture, are the least likely to get all their credits. Only half of these projects come to fruition, according to Point Carbon, a consultancy.

Some 1,950 projects have been registered with the UN's Clean Development Mechanism, which issues carbon credits under the Kyoto protocol. Each credit represents a tonne of carbon dioxide that was reduced, and they are awarded to projects such as wind farms and solar power generation, in developing countries. The credits are bought by rich countries, which can count them towards their targets to reduce emissions under Kyoto.