Malte Meinshausen, Louise Jeffery, Johannes Guetschow, Yann Robiou du Pont, Joeri Rogelj, Michiel Schaeffer, Niklas Höhne, Michel den Elzen, Sebastian Oberthür, and Nicolai Meinshausen

Nature Climate Change, 26th October 2015, dx.doi.org/10.1038/nclimate2826

National post-2020 greenhouse gas targets and diversity-aware leadership

Background slides.

Embargo until 26th October 2015; 16:00 London Time

The problem

1. All countries agree to keep global mean temperatures at least below 2°C.

2. All the countries‘ self-set targets are 2°C compatible under their own understanding of fairness.

3. Adding up all countries‘ emissions, a least-cost path towards staying below 2°C will however be missed by a wide margin.

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One solution

1. A major economy, say ‚country A‘, starts to lead in the international climate effort and sets an ambitious target.

2. All other countries adopt ‚comparable‘ targets to that country A. Comparable under their own understanding of fairness.

3. If the target of country A is sufficiently ambitious, a self-differentiation can then enable the collective 2°C target to be achieved.

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What are 2°C compatible emissions?

By 2025:•Lower global emissions to 15% below 2010, which is 10% above 1990 levels.

By 2030: •Lower global emissions to 22% below 2010, which is 1990 levels.

Those are approximately median values for any IPCC AR5 pathway that stays within the 1000 GtCO2 cumulative carbon budget limit. Methods see paper.

Fig.

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Current INDCs and leadership targets of USA, EU28 and ChinaGlobal emission shares: •China accounts for a quarter of global emissions, 25%, in 2010.•Next biggest emitter was the USA with 16%. •EU28 comes in third with 11%.

INDCs:•China‘s INDC is a ‚peaking by 2030‘ pledge combined with an intensity target, quantified at approximately 35% above 2010 emissions by 2030 •The INDC of the USA is a 26-28% reduction below 2005 by 2025. •The INDC of the EU28 is a 40% reduction below 1990 by 2030.

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The pie represents global GHG emissions in 2010, incl. landuse. Colors correspond to the regions as indicated in the world map. Main emission data source is PRIMAP, a composite dataset combining UNFCCC official data, where available, CDIAC, EDGAR and other authoritative data sources.

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48 Gt

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The pie represents global GHG emissions in 2010, incl. landuse. Colors correspond to the regions as indicated in the world map. Main emission data source is PRIMAP, a composite dataset combining UNFCCC official data, where available, CDIAC, EDGAR and other authoritative data sources.

48 Gt

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The pie represents global GHG emissions in 2010, incl. landuse. Colors correspond to the regions as indicated in the world map. Main emission data source is PRIMAP, a composite dataset combining UNFCCC official data, where available, CDIAC, EDGAR and other authoritative data sources.

48 Gt

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48 Gt

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Percentages indicate changes of 2025 emissions (colored

areas) relative to 2010 emissions (grey areas in

background).

Percentages indicate changes of 2025 emissions (colored

areas) relative to 2010 emissions (grey areas in

background).

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World emissions by 2025 would be 6% above 2010 levels, if other countries adopted ‚comparable‘

targets to the US. Comparability taken as the more favourable approach

for every country.

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If the USA were to adopt a target of -52% below its 2010 levels (54% below 2005), global emissions

could be 15% below 2010, which is the 2°C waypoint.

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By 2030, if every country ‚followed‘ Australia‘s

target of 26-28% below 2005, then global

emissions would be 2% above 2010 levels.

By 2030, Australia would have to reduce its

emissions by 66% in order to act as leading by

example, putting the world on a 2°C track.

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By 2030, world emissions would be practically at

2010 levels, if all countries were to follow the 40% EU target (which is 27% below

2010).

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By 2030, the EU28 would have to reduce 61% below 2010 or 67% below 1990, if the world should regard EU28 as a leader and be

on a 2°C track.

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If all countries were to follow China, with a

supposedly 35% increase of emisisons until 2030 over 2010, then global

emissions would increase by a third.

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China would have to reduce its emissions by

about a third, rather than increase by a third, in order to be a leading

example for other countries and put the world on a 2°C track.

Country US(2025)

EU(2030)

China(2030)

Australia(2030)

INDC(announced)

-26 to -28% (on 2005 levels)

40% (on 1990 levels) Peak by 2030 -26 to -28%

(on 2005 levels)

INDC(on 2010 levels) -22 to -24% -27% +35%

(estimate) -23 to -25%

Towards Distributive justice -29% -41% -32% -30%

Corrective justice -51% -49% -4% -65%

Leadership(on 2010 levels)

-52% -61% -32% -66%

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More information & interactive results at:

www.mitigation-contributions.org An interactive data appendix with this study‘s results, allowing the user to probe any G20 country‘s target, if other world countries were doing ‚the same‘. The paper is available from 26th October 2015, 4pm London time: dx.doi.org/10.1038/nclimate2826