The UNEP report is particularly relevant to the short-term situation given that the international community has agreed to limit future warming to prevent catastrophic warming to 2° C or perhaps 1.5° C if later studies demonstrate that a 1.5° C warming limit is necessary to prevent catastrophic harms.
The UNEP report found that even if nations meet their current climate pledges, ghg emissions in 2020 are likely to be 8 to 12 gigatonnes of CO2 equivalent (GtCO2e) above the level that would provide a likely chance of remaining on the least-cost pathway.
To be on track to stay within the 2° C target and head off very dangerous climate change, the report says that emissions should be a maximum of 44 GtCO2e by 2020 to set the stage for further cuts needed keep warming from exceeding the 2° C target.
Since total global ghg emissions in 2010 already stood at 50.1 GtCO2e, and are increasing every year, reaching a 44 GtCO2e target by 2020 is extraordinarily daunting and much greater ambition is needed from the global community than can be seen in existing national ghg emissions reduction commitments.
UNEP pointed out in its report that the 44 GtCO2e target by 2020 is necessary to have any hope of achieving even greater cuts needed after 2020 when total emissions must be limited to sharply declining total emissions limitations. Moreover if the world continues under a business-as-usual scenario, which does not include pledges, 2020 emissions are predicted to reach 59 GtCO2e, which is 1 GtCO2e higher than was estimated in a UNEP report issued in 2012. Without doubt increasing the ambition of national ghg commitments is urgently needed to provide any reasonable hope of limiting warming to non-catastrophic levels.
The September, 2013, IPCC issued a report which contained a budget on total carbon emissions that the world needs to stay within to give a 66% chance of preventing more than the 2° C warming that attracted world attention despite the fact that it has been widely criticized as being overly optimistic. This budget is an upper limit on total human CO2 equivalent emissions from the beginning of the industrial revolution until the day we stop burning carbon. The IPCC said that for warming to remain below last 2° C warming limit, the total amount of CO2 must be less than 1000 billion tons.
The IPCC report estimated that we’ve already used 531 billion tons of that budget as of 2011 by burning fossil fuels for energy as well as by clearing forests for farming and myriad other uses. That means would mean that there is 469 tons left in the emissions budget. This further means that the budget would be completely used up by current emissions by around 2044, just over 30 years from now.