27 November 2015
More than 190 countries are meeting in Paris next week to create a durable framework for addressing climate change and to implement a process to reduce greenhouse gases over time. A key part of this agreement would be the pledges made by individual countries to reduce their emissions. An article published in Science today shows that the Paris pledges can reduce the probability of extreme levels of warming beyond 4°C and increase the probability of limiting global warming to 2°C, but require a robust process that allows ambition to continuously increase over time to achieve this.
In the lead up to the Paris meetings, countries have announced the contributions that they are willing to make to combat global climate change, based on their own national circumstances. These Intended Nationally Determined Contributions, or INDCs, take many different forms and extend through 2025 or 2030. Examples of these commitments include the United States' intention to reduce emissions in 2025 by 26-28% of 2005 levels, the EU’s vow to reduce its emissions in 2030 by 40% of 1990 levels, and China's pledge to peak emissions by 2030 and increase its share of non-fossil fuels. In the study, the scientists tallied up these INDCs and simulated the range of temperature outcomes the resulting emissions would bring in 2100 under different assumptions about possible emissions reductions beyond 2030.
“We wanted to understand what Paris can mean from a risk management perspective," said climate scientist Joeri Rogelj of the International Institute for Applied Systems Analysis, a co-author of the study. "We not only looked at what current country proposals mean for the well-known 2-degree limit, but also what they imply for much more dramatic warming."
Although many researchers have focused on the importance of the 2°C limit, the study assessed uncertainty in the climate change system from an overall risk management perspective. The researchers analyzed the full range of temperatures the INDCs might attain, and determined the odds for achieving each of those temperatures. To determine odds, they modeled the future climate hundreds of times to find the range of temperatures these various conditions produce.
“It’s not just about 2 degrees,” said Dr. Gokul Iyer, the study's lead scientist at the Joint Global Change Research Institute in the United States, “It is also important to understand what the INDCs imply for the worst levels of climate change.”
In the study, the scientists compare the Paris commitments to a world in which countries don't act at all or start reducing greenhouse gas emissions only in 2030.
The team found that if countries do nothing to reduce emissions, the Earth has almost no chance of staying under the 2°C limit, and it is likely that the temperature increase would exceed 4°C. They went on to show that the INDCs and the future abatement enabled by Paris introduce a chance of meeting the 2°C target, and greatly reduce the chance that warming exceeds 4°C. The degree to which the odds are improved depends on how much emissions limits are tightened in future pledges after 2030.
“Long-term temperature outcomes critically hinge on emissions reduction efforts beyond 2030,” says Iyer. “If countries implement their INDCs through 2030 and ramp up efforts beyond 2030, we’ll have a much better chance of avoiding extreme warming and keeping temperature change below 2°C.”
“If we consider Paris the finish line, we will fail to protect our climate. It needs to be a starting point for further action,” explains Rogelj. “Clear steps that show how emissions can be further reduced over time are critical for a lasting legacy of Paris.”
Iyer said the next thing to look at was the question of what kinds of policies and institutional frameworks could pave the way for a robust process that enables emissions reduction efforts to progressively increase over time.
Allen A. Fawcett, Gokul C. Iyer *, Leon E. Clarke , James A . Edmonds, Nathan E. Hultman, Haewon C. McJeon, Joeri Rogelj, Reed Schuler, Jameel Alsalam, Ghassem R. Asrar, Jared Creason , Minji Jeong, James McFarland, Anupriya Mundra, Wenjing Shi, (2015). Can Paris Pledges Avert Severe Climate Change? Science November 26, 2015
Last edited: 26 November 2015
IIASA research at the Paris Climate Change Conference 2015
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