Effect of current pledges and policies on global temperature

 

 

Data underlying the above graph can be downloaded here

 

Addressing global warming

In the absence of policies global warming is expected, to reach 4.1°C – 4.8°C above pre-industrial by the end of the century. The emissions that drive this warming are often called Baseline scenarios (‘Baselines’ in the above figure). and are taken from the IPCC AR5 Working Group III. Current policies presently in place around the world are projected to reduce baseline emissions and result in about 3.6°C  [1] warming above pre-industrial levels. The unconditional pledges or promises that governments have made, including in submitted INDCs as of 7 December 2015, would limit warming to about 2.7°C [2] above pre-industrial levels, or in probabilistic terms, likely limit warming below 3°C.

There remains a substantial gap between what governments have promised to do and the total level of actions they have undertaken to date. Furthermore, both the current policy and pledge trajectories lie well above emissions pathways consistent with a 1.5°C or 2°C world.

 

Evaluating progress towards the below 2°C and 1.5°C limits

Limiting warming to the globally agreed goal of holding warming below a 2°C increase above pre-industrial in the 21st century means that the emissions of greenhouse gases need to be reduced rapidly in the coming years and decades, and brought to zero shortly after mid-century.  Vulnerable countries, small island states and least developed countries, have called for warming to be limited to below 1.5°C by 2100. As a consequence the adequacy of the 2°C limit is being reviewed in a formal UNFCCC process where the merits of the 1.5°C limit are also being examined [3]

The CAT evaluates progress towards these global goals by quantifying the aggregate effects of current policies and the pledges (promises) and INDCs put forward by countries, and compares these with the emissions levels consistent over time with both the 1.5°C and 2°C warming limits.

 

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 INDCs until 7 December) gives a 50% chance of warming being 2.7°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.

 

December 2015 - INDCs likely below 3°C and over 90% chance exceeding 2°C

The emissions pledge pathway that includes INDCs has aover 90% probability of exceeding 2°C, and only a ‘likely’ (>66%) chance of remaining below 3°C this century. The current policy pathways have a higher than 99.5% probability of exceeding 2°C.


Limiting warming to 2°C with ‘likely’ probability

In the CAT we assess pathways against a (>66%) probability of holding warming below 2°C. A median 2°C pathway would give, in effect, only a ‘toss of the coin’ chance of limiting warming below this level. It is assumed that policy makers are interested in a higher probability of achieving this limit. A higher probability of limiting warming below 2°C gives greater confidence that the emissions reduction efforts made will be successful in limiting warming to 2°C. This means, of course, that the median peak warming from a 2°C compatible pathway will be lower than 2°C - in the range of 1.5-1.7°C (see figure above and IPCC AR5 WGIII Ch6).


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.[4]

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.[5]


Further information
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 / New Climate / PIK team!

Last temperature update: 7 December 2015. 'Pledges' include all INDCs submitted by 7 December.

 



[1] 3.6 is the median of the low and high ends of current policy projections (3.3 to 3.8°C). The uncertainty range on the figure (2.7-4.9°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] The uncertainty range for pledges on the CAT thermometer (2.2-3.4°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. If the more ambitious end of pledge ranges were reached, warming could be limited to a median of 2.5°C. This includes the upper end of country INDCs where a reduction range is specified (e.g. the 28% end of the 26-28% commitment by the USA), and mitigation commitments that are conditional on finance (e.g. 101 Mt CO2-e by Trinidad & Tobago).

[3] http://unfccc.int/science/workstreams/the_2013-2015_review/items/6998.php

[4] The IPCC AR5 WGIII identified many mitigation options to hold warming below 2°C (with a likely chance), and with central estimates of 1.5-1.7°C by 2100. The IPCC further shows that  “a limited number of studies have explored scenarios that are more likely than not to bring temperature change back to below 1.5°C by 2100”.  The scenarios indicating the feasibility of bringing temperatures down below 1.5°C are “characterised by (1) immediate mitigation action; (2) the rapid upscaling of the full portfolio of mitigation technologies; and (3) development along a low-energy demand trajectory.” (IPCC WGIII SPM page 17). The 0.06 per cent figure is median of the range 0.04 to 0.14, Table SPM.2, IPCC AR5 WGIII page 15. For consumption growth figures refer to page 16.

[5] Refer to CAT Briefing "The CAT Emissions Gap - How close are INDCs to 1.5 and 2 pathways?", September 2015.