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Changes in temperature estimates

4th September 2012

The current Climate Action Tracker (CAT) analysis estimates that pledges under the most likely scenario result in a warming of 3.3°C with a 68% confidence interval of 2.6-4.1°C. The previous analysis published in Durban in December 2011 shows a warming of 3.5°C by 2100 for the minimum ambition pathway. The Durban results were 0.3°C higher compared to previous calculations. Current changes result from using a recently updated version of the PRIMAP climate module (which is based on the simple coupled carbon-cycle and climate model MAGICC) and updated emission and pledge data. This technical paper explains where the differences come from in more detail.

Current calculations are based on a series of updates and changes that result in changes in predicted warming. These are:

  • Update of the PRIMAP climate module used to calculate the temperature rise from the emission pathways;
  • Updates and changes in baseline and pledge pathway calculations, including improvements in the pathway calculation and new releases of data (such as UNFCCC national inventories).

The changes in the climate module amount to a difference of -0.07°C. The changes in the emission pathways result in a total difference of -0.16°C, which is split equally between changes in the pathway creation algorithms and changes due to the use of new data sources.

You can download the full technical paper here.