How much carbon emissions have we got left in the future with the new global warming target of 1.5°C that was set in Paris? And how can the remaining carbon budget be shared fairly between almost 200 countries?
Last year we published an article on whether country emission pledges were a ‘fair and ambitious’ way to keep global average temperatures 2°C below preindustrial levels. Here, we update that analysis for a 1.5°C temperature level.
Translating pledges into future carbon emissions
In the Paris agreement, the world’s nations agreed to limit global warming to well below 2°C, pursuing 1.5°C. While the temperature goal is set globally, its implementation will happen ‘bottom-up’ through country-level emission pledges, called (Intended) Nationally Determined Contributions (INDCs or NDCs).
Scientists can help translate the global ambition level into the total amount of carbon dioxide emissions that can be emitted in the future. However, how do we ensure in a bottom-up process that future carbon emissions are shared fairly between countries? Assessing whether the national emissions pledges are ‘fair and ambitious’ is fraught with difficulty.
In 2015, we developed a framework to compare the consistency of countries’ current emission pledges to the ambition of keeping global temperatures below 2°C. We compared the allowable cumulative emissions of carbon dioxide with the emission pledges of the EU, USA, China, and India. We found that, combined, the EU, US, Chinese, and Indian emission pledges leave no room for other countries to emit CO2 if a 2°C temperature limit is respected.
How much is left?
Updating our 2015 study, we can emit about 850 billion tonnes of CO2 in the future before exceeding 2°C. This is equivalent to about 25 years of emissions at current levels.
After adjusting our estimates for 1.5°C, we find that we can emit about 200 billion tonnes of CO2 before exceeding 1.5°C. This is equivalent to about 5 years of emissions at current levels.
These future allowable emissions are not fixed, however. Most emission pathways in the Fifth Assessment Report by the UN’s climate panel IPCC assume that we can remove carbon dioxide from the atmosphere to keep below 1.5°C and 2°C (so-called negative emissions). This means sequestering carbon in new forests or, primarily, through technologies that combine carbon-neutral bioenergy with carbon capture and storage. Recent studies have shown that the scale of carbon dioxide removal required in the emission scenarios is highly contentious.
We believe it is more realistic to assume that we will be able to remove some carbon dioxide from the atmosphere, but not in sufficient amounts to take global emissions below zero. If we assume that emissions cannot go below zero, then we can only emit 200 billion tonnes CO2 to be consistent with 1.5°C and 850 billion tonnes CO2 to be consistent with 2°C.
What is a fair share?
The emissions pledges of the USA, EU, India, and China use all the remaining emissions for 1.5°C and leave very little room for the rest of the world to emit for 2°C.
We further compare how the remaining 200 or 850 billion tonnes CO2 could be shared between countries, by comparing the emission pledges for each country to two potential end-points:
- ‘Inertia’ shares the remaining emissions based on the current distribution of emissions;
- ‘Population’ shares the remaining emissions based on the current distribution of population.
In both cases, and for all countries, the emission pledges do not fall in what could be called a ‘fair’ pathway.
China and India, in particular, face a difficult challenge. Their economies and emissions are growing fast (despite a recent slowdown in China). Each year that their emissions grow, they will move further away from obtaining the necessarily net-zero emissions. China and India need to implement policies to slow and then peak emissions, before leading to a rapid decline in emissions towards zero.
Developed countries, such as the USA and EU, are already reducing their emissions but these reductions have to be increased. Indications are that this is technically possible, but it requires aligning political and societal priorities.
Summing up, our analysis shows that the emissions pledges are inconsistent with a 'fair and ambitious' pathway to 2°C and even not remotely consistent with a pathway consistent with 1.5°C. It is clear that countries need to increase their level of ambition.