Statistical Tools Help Estimate Future Outcomes of Paris Agreement Targets

Early in 2017, statistical tools were used in a broadly-cited study to model the likely future outcomes of the global temperature targets set by the Paris Agreement.

For the top 10 emitters, this is the percentage increase in the country’s emissions-reductions targets that would be required to achieve the Paris Agreement’s goal of keeping warming to 2 degrees C this century. Countries that set more ambitious goals or that have made substantial progress already need a smaller boost now. Russia is not included, since it has exceeded its Paris Agreement commitments. Image Credit: P. Liu and A. Raftery/Communications Earth & Environment.

The study discovered that on present-day trends, the Earth had just a 5% probability of remaining under the 2°C warming goal this century—the supposed goal of the international climate treaty.

The same authors have now utilized their statistical tools to ask what kinds of emissions cuts would truly be needed to fulfill the goal of 2°C warming, which is regarded as a threshold for climate stability as well as climate-related risks, like drought, excessive heat, sea-level rise and extreme weather

The study performed by the University of Washington found that emissions reductions on an average of 1.8% drop in emissions annually rather than 1% annually, or around 80% more ambitious than those in the Paris Agreement, would be sufficient to stay within the 2°C goal. The study results were published in Nature’s open-access journal, Communications Earth & Environment, on February 9th, 2021.

A number of people have been saying, particularly in the past few years, that the emissions targets need to be more ambitious. We went beyond that to ask in a more precise way: How much more ambitious do they need to be?

Adrian Raftery, Study Lead Author and Professor of Statistics, University of Washington

The new article employs the same statistical method to model the three key drivers of human-induced greenhouse gases—that is, gross domestic product per person, national population, and the amount of carbon produced for every dollar of economic activity, called carbon intensity.

Next, it utilized a statistical model to demonstrate the range of possible future outcomes based on the projections and data, to date.

But even with updated techniques and five additional years of data, currently covering from 1960 to 2015, the conclusion still remains almost the same as that of the earlier analysis: that is, meeting Paris Agreement targets would give just a 5% chance of staying below the 2°C warming goal.

Presuming that economic growth or population growth will not be targeted by climate policies, the study authors then asked about the kind of change that would be required in the 'carbon intensity' measure to fulfill the 2°C warming goal.

Raising the overall targets to reduce carbon emissions by an average of 1.8% per year, and persisting on that path after the end of the Paris Agreement in 2030, would give the world only a 50% probability of staying below the 2°C warming goal by 2100.

Achieving the Paris Agreement’s temperature goals is something we’re not on target to do now, but it wouldn’t take that much extra to do it.

Peiran Liu, Study First Author, University of Washington

Liu had performed the study as part of his doctorate at the University of Washington.

The article also considered the implications behind this overall strategy of the Paris Agreement commitments made by different nations. Countries have set their own Paris Agreement emissions-reductions pledges.

As such, the U.S. has pledged a 1% cut in carbon emissions annually until 2026, or somewhat more ambitious than the average set by the Paris Agreement. China has pledged to decrease its carbon intensity, or the carbon emissions for each unit of economic activity, by as much as 60% of its 2005 levels by 2030.

Globally, the temperature goal requires an 80% boost in the annual rate of emissions decline compared to the Paris Agreement, but if a country has finished most of its promised mitigation measures, then the extra decline required now will be smaller.

Peiran Liu, Study First Author, University of Washington

Supposing that each nation’s share of the work stays unchanged, then the United States would be required to raise its goal by as much as 38% to contribute its part toward truly achieving the 2°C warming goal.

On the other hand, China’s fairly effective and more ambitious strategy would need just a 7% increase, while the United Kingdom, which has already made considerable progress, would need a 17% boost. Conversely, nations that had pledged emissions cuts but where emissions have increased, such as Brazil and South Korea, would now need a larger boost to counteract the lost time.

The study authors also recommended that nations should increase their accountability by assessing the progress every year and not on the five year, 10 year, or longer timescales factored in several prevailing climate plans.

Raftery added, “To some extent, the discourse around climate has been: ‘We have to completely change our lifestyles and everything. The idea from our work is that actually, what’s required is not easy, but it’s quantifiable. Reducing global emissions by 1.8% per year is a goal that’s not astronomical.”

According to Raftery, from 2011 to 2015 period, the U.S. did observe a drop in emissions, because of efficiencies in sectors spanning from transportation to lighting as well as regulation. The economic changes caused by the pandemic will be brief, he predicted; however, the flexibility and creativity required by the pandemic maul read to a permanent drop in emissions.

If you say, ‘Everything’s a disaster and we need to radically overhaul society,’ there’s a feeling of hopelessness. But if we say, ‘We need to reduce emissions by 1.8% a year,’ that’s a different mindset,” Raftery concluded.

The National Institutes of Health ash funded the study.

Journal Reference:

Liu P R & Raftery A E (2021) Country-based rate of emissions reductions should increase by 80% beyond nationally determined contributions to meet the 2 °C target. Communications Earth & Environment.


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