The CAT Thermometer explained
The temperatures on the CAT thermometer are ‘median’ warming estimates in 2100. It means that there is a 50% chance that the calculated temperature would be exceeded if the given emissions pathway were followed.
For example, our emissions pathway in the pledge scenario (that incorporates NDCs until 01 November 2017) gives a 50% chance of warming being 3.16°C or higher in 2100.
Using probabilities to provide more information
The ‘median’ is based on the probability distribution generated by the climate model (MAGICC) when it takes into account uncertainties in our knowledge of climate sensitivity, the carbon cycle, and effect of greenhouse gases, aerosols, and other factors that are used to calculate the temperatures. The probability distribution enables us to provide more information for policy makers and stakeholders about the likelihood of goals being met, or specific temperatures being exceeded.
November 2017 NDCs likely below 3.5°C and over 90% chance exceeding 2°C
The emissions pledge pathway that includes (I) NDCs has over 90% probability of exceeding 2°C. The current policy pathways have a higher than 97% probability of exceeding 2°C.
What governments need to do to achieve the global goal
Fortunately, as shown by the IPCC AR5, substantially more action, sufficient to hold warming below 2°C (and to below 1.5°C by 2100) with likely probability is technically and economically feasible. According to the IPCC, the costs of reducing emissions to limit warming to below 2°C are modest, even before taking into account co-benefits such as increased energy-security and health improvements due to reduced air pollution. Annualised reductions of consumption growth are estimated at around 0.06 per cent over the century, relative to a baseline of 1.6 to 3% growth per year.
The IPCC AR5 shows that even starting from emission levels implied by INDCs and current policy projections, 1.5°C and 2°C pathways are still technically feasible. However, the resulting emission pathways are increasingly expensive as they are not consistent with the most cost-efficient policies. Slower-than-optimal emission reductions early on need to be followed by faster reductions later on, effectively leading to significantly higher costs for the period 2030–2050 than would otherwise be needed. While the challenges are significant, limiting warming to below 1.5°C by the end of the century is still feasible from current emissions levels. However, with every decade lost, these challenges and costs rise and will, at some point, become insurmountable with warming locked in to 1.5 or 2°C and above. 
For more information on the global emission pathways and how they are calculated, please see the detailed analysis and methodology pages.
If you use the provided data or any of the graphs provided on this website, please make sure to reference the Climate Action Tracker and the Ecofys / Climate Analytics / NewClimate team!
Last temperature update: 6 November 2017.
1 | 3.4°C is the median of the low and high ends of current policy projections (3.1 to 3.7°C). The uncertainty range on the figure (2.5-4.7°C) originates from carbon-cycle and climate modelling around both the low and high current policy projections. Here we give the 68% range; that is the 16th and 84th percentiles of the probability distribution.
2 | Refer to CAT Briefing "The CAT Emissions Gap - How close are INDCs to 1.5 and 2 pathways?", September 2015.