Recent pledges for national climate action are vague, complicated and barely comparable, casting doubt over the transparency of a prospective global agreement to be reached later this year.
Countries have promised to submit pledges for climate action ahead of a summit in Paris at the end of this year.
In Paris, they are expected to reach a major agreement setting targets for action beyond 2020, for greenhouse gas emissions, financing and measures to adapt to climate change.
The emissions pledges that countries have submitted so far show all of the problems of leaving the task of setting targets to countries themselves.
Comment: UN needs to take control of Paris pledges
The Paris process follows past agreements in Kyoto in 1997, in Copenhagen in 2009 and in Cancun in 2010.
The Kyoto Protocol was a top-down process, where countries negotiated formal, rules-based emissions targets for industrialised nations.
To try and involve developing countries, the Copenhagen and Cancun agreements left it up to countries to decide their own targets voluntarily, rather than negotiate these in advance.
The Paris agreement is also following this voluntary approach, allowing countries to set their own targets. The aim is also to borrow some of the formal, rules-based approach of the Kyoto Protocol, to make some aspects of the agreement legally binding.
The signs so far are not good, as the pledges submitted to date are barely comparable:
1. They target different years, either 2025 or 2030, and with different baselines, including 1990, 2005 and 2013
2. Use different treatments of aspects which will have enormous impact on their ambition, for example whether they will allow the use of international carbon offsets and forest carbon sinks
3. Use different approaches for setting emissions targets, whether absolute emissions, or targets based on the carbon intensity of GDP, or compared with business as usual emissions
4. Measure different greenhouse gases (GHGs), including all the main GHGs, or just carbon dioxide (CO2)
5. In some cases have a range of ambition, raising the question which end of the range is the main target.
Perhaps most seriously, there is a question mark over the quality of national reporting of historical emissions. If this is just educated guesswork, then the targets are meaningless.