Was Cancun a success? Well, countries, except brave Bolivia who dared to quote the science, did agree on something - which is an achievement of sorts.
But although progress was made on a number of issues to do with accounting for a nation's emissions and verifying their actions, none of the decisions made at Cancun are yet sufficient to lead to quantifiable changes.
According to Climate Action Tracker, which provides an independent peer-reviewed assessment of emission reduction proposals, the largest factors limiting emissions savings are:
Surplus emissions allowances
Countries will currently be able to sell and buy allowances originally meant for the period up to 2012 beyond that date. If so, this could mean that taken together, developed countries wouldn't need to do anything further to curb emissions until at least 2020. This would add about 3-9% relative to 1990 to the emission limits, and credits would still not be exhausted until 2025-2030.
Forests and land use
The options for accounting for the impact of a country's forests, land-based emissions, deforestation and reforestation are not finally agreed. By 2020 they could cause a nation's emissions to be 3% more than they would otherwise be relative to 1990.
Japan has a relatively ambitions 25% reduction target below 1990 by 2020, but it is likely to be met by offsetting in developing countries. As these actions would be counted by those countries, this would mean double-accounting.
There's scant chance of federal greenhouse gas legislation in the USA. This means their 2050 target is unlikely to be met. Double counting of offsets is a problem for America and its partners too.
The gap between hope and action
With business carrying on as at present, global emissions by 2020 will be 56 billion tonnes CO2equiv/year. To limit warming to 2°C or 1.5°C, they would need to be in the range of 44-40 billion tonnes by 2020, a reduction of 22-29%, or 12-16 billion tonnes, at a rate of over two billion tonnes per year.
The promises made at Cancun lie in a range from low ambition to high. If the lowest were attained by 2020, there would be a reduction of just 3 billion tonnes, leading to an average global temperature raise that is highly unacceptable, of 3.2oC.
If the highest ambition targets were reached in 2020, this would only add another 1.3 billion tonnes of cuts, to 51.7 billion tonnes per year.
The gap is therefore between 8 and 12 billion tonnes per year in 2020.
How can the gap be closed?
The Climate Action Tracker has identified several options which would achieve more than enough to close the gap:
• The decision on how many emissions allowances could be carried over by nations after 2012 has yet to be taken. Therefor it is possible to eliminate new surplus emissions ‘built into’ 2020 reduction pledges; options for this are included in the negotiating text
• Remove crediting for forestry and land use that allow developed countries to increase their emissions
• Reduce international aviation and marine emissions up to half of the projected levels in 2020
• Increase ambition level of developed countries as a group - in line with the European Union's aspiration - to a 30% cut below 1990 in 2020 (without forestry credits)
• Ensure reductions of emissions in developing countries of 1.5 - 6.2 billion tonnes
• Halt deforestation by 2020.
Crucially, global long-term emission reductions are required as well: at least 50% below 1990 by 2050. The UK's Climate Change Committee advocated 60% last week. The Cancun climate conference did not include a goal for 2050.