Starting from COP 19, the World Climate Conference held in Warsaw in 2013, governments decided to commit to officially declaring their pledges on reducing greenhouse gas emissions. With just a few weeks to go until COP 21, which will be held in Paris from 30 November, 155 countries have made their promises known. These, however, vary considerably from one another.

While the US has declared a reduction in emissions of 26–28 per cent to be achieved by 2025 (compared to 2005 levels), the European Union has aimed for a 40 per cent decrease to be reached by 2030 (compared to 1990 figures). India, meanwhile, has targeted a reduction of 33–35 per cent, while Russia is aiming for minus 25–30 per cent. And China has not promised a reduction, but rather a "peak" to be reached by 2030. Some governments have also preferred to use as a reference point for calculating their reduction not a specific year, but the figure known as "business as usual" ("BAU", in the table showing data for the fifteen largest emitters of harmful gases in the world): reductions are calculated, in this case, relative to the emissions that would be reached in the future if no corrective action were taken.

In an attempt to bring some clarity, and to understand the true combined worth of the pledges announced, the United Nations has prepared a report taking into account 146 promises (those submitted by 1 October). The Executive Secretary of the UNFCCC (United Nations Framework Convention on Climate Change), Christiana Figueres, has explained that – to date – these pledges "will lead to limiting the rise in average global temperature, by the end of the century, to 2.7 degrees Celsius." That is well beyond the limit set by the governments themselves, of 2 degrees, which is necessary to avoid catastrophic consequences.

The pledges, then, are not sufficient. All the more so given that NGOs consider even the UN's assessment to be optimistic. According to Nicolas Hulot, president of the French foundation bearing his name (and "special envoy" of the Paris government to COP 21), "at the current rate, we will exceed the threshold of 3 degrees Celsius." For this reason, he added, it is essential that governments periodically review their commitments in the future: "The G20 countries, responsible for three quarters of global emissions, could take this initiative, and redefine their promises as early as 2016 or 2017."

Governments, however, still appear quite divided. And at the beginning of November came the unexpected news of China revising its pollution data upwards. The world's largest contributor to greenhouse gas emissions admitted that it had significantly underestimated coal use on its territory. This means that the statistics published up to now were missing approximately one billion tonnes of CO2 released into the atmosphere — equivalent to the annual emissions of a country like Germany.