Can Paris pledges avert severe climate change?

November 26, 2015

COLLEGE PARK, Md. - 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.

A study published in Science today shows that if implemented and followed by measures of equal or greater ambition, the Paris pledges have the potential to reduce the probability of the highest levels of warming, and increase the probability of limiting global warming to 2 degrees Celsius.

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' vow to reduce emissions in 2025 by 26-28 percent of 2005 levels and China's pledge to peak emissions by 2030 and increase its share of non-fossil fuels in primary energy consumption to around 20 percent. 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 know how the commitments would play out from a risk management perspective," said economist Allen Fawcett of the U.S. Environmental Protection Agency, the lead author of the study. "We analyzed not only what the commitments would achieve over the next ten to fifteen years, but also how they might lay a foundation for the future."

Although many researchers have focused on the importance of the 2 degree limit, Fawcett and colleagues assessed uncertainty in the climate change system from an overall risk management perspective. They 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 Gokul Iyer, the study's lead scientist at the Joint Global Change Research Institute, a collaboration between the Department of Energy's Pacific Northwest National Laboratory and the University of Maryland. "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 degree limit, and it is likely that the temperature increase would exceed 4 degrees. They went on to show that the INDCs and the future abatement enabled by Paris introduce a chance of meeting the 2 degree target, and greatly reduce the chance that warming exceeds 4 degrees. The extent 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," said 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 degrees Celsius. It's important to know that the INDCs are a stepping stone to what we can do in the future."

To perform the analysis, the team incorporated the INDCs along with assumptions about future emissions reductions into a global, technologically detailed model of the world called the Global Change Assessment Model or GCAM that includes energy, economy, agriculture and other systems. The GCAM model produced numbers for global greenhouse gas emissions, which the team then fed into a climate model called Model for the Assessment of Greenhouse-gas Induced Climate Change or MAGICC. Running the simulations for each scenario 600 times resulted in a range of temperatures for the year 2100, which the team converted into probabilities.

Iyer said the next thing to look at was the question of the kinds of policies and institutional frameworks that could pave the way for a robust process that enables emissions reduction efforts to progressively increase over time.
-end-
This work was supported by the Global Technology Strategy Program, the William and Flora Hewlett Foundation, the Department of State, and the Environmental Protection Agency.

Reference: Allen A. Fawcett, Gokul 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. Can Paris Pledges Avert Severe Climate Change, Science, November 26, 2015, doi: 10.1126/science.aad5761

Interdisciplinary teams at Pacific Northwest National Laboratory address many of America's most pressing issues in energy, the environment and national security through advances in basic and applied science. Founded in 1965, PNNL employs 4,400 staff and has an annual budget of nearly $1 billion. It is managed by Battelle for the U.S. Department of Energy's Office of Science. As the single largest supporter of basic research in the physical sciences in the United States, the Office of Science is working to address some of the most pressing challenges of our time. For more information on PNNL, visit the PNNL News Center, or follow PNNL on Facebook, Google+, LinkedIn and Twitter.

DOE/Pacific Northwest National Laboratory

Related Climate Change Articles from Brightsurf:

Are climate scientists being too cautious when linking extreme weather to climate change?
Climate science has focused on avoiding false alarms when linking extreme events to climate change.

Mysterious climate change
New research findings underline the crucial role that sea ice throughout the Southern Ocean played for atmospheric CO2 in times of rapid climate change in the past.

Mapping the path of climate change
Predicting a major transition, such as climate change, is extremely difficult, but the probabilistic framework developed by the authors is the first step in identifying the path between a shift in two environmental states.

Small change for climate change: Time to increase research funding to save the world
A new study shows that there is a huge disproportion in the level of funding for social science research into the greatest challenge in combating global warming -- how to get individuals and societies to overcome ingrained human habits to make the changes necessary to mitigate climate change.

Sub-national 'climate clubs' could offer key to combating climate change
'Climate clubs' offering membership for sub-national states, in addition to just countries, could speed up progress towards a globally harmonized climate change policy, which in turn offers a way to achieve stronger climate policies in all countries.

Review of Chinese atmospheric science research over the past 70 years: Climate and climate change
Over the past 70 years since the foundation of the People's Republic of China, Chinese scientists have made great contributions to various fields in the research of atmospheric sciences, which attracted worldwide attention.

A CERN for climate change
In a Perspective article appearing in this week's Proceedings of the National Academy of Sciences, Tim Palmer (Oxford University), and Bjorn Stevens (Max Planck Society), critically reflect on the present state of Earth system modelling.

Fairy-wrens change breeding habits to cope with climate change
Warmer temperatures linked to climate change are having a big impact on the breeding habits of one of Australia's most recognisable bird species, according to researchers at The Australian National University (ANU).

Believing in climate change doesn't mean you are preparing for climate change, study finds
Notre Dame researchers found that although coastal homeowners may perceive a worsening of climate change-related hazards, these attitudes are largely unrelated to a homeowner's expectations of actual home damage.

Older forests resist change -- climate change, that is
Older forests in eastern North America are less vulnerable to climate change than younger forests, particularly for carbon storage, timber production, and biodiversity, new research finds.

Read More: Climate Change News and Climate Change Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.