Earth likely to warm more than 2 degrees this century

July 31, 2017

Warming of the planet by 2 degrees Celsius is often seen as a "tipping point" that people should try to avoid by limiting greenhouse gas emissions. But the Earth is very likely to exceed that change, according to new University of Washington research. A study using statistical tools shows only a 5 percent chance that Earth will warm 2 degrees or less by the end of this century. It shows a mere 1 percent chance that warming could be at or below 1.5 degrees, the target set by the 2016 Paris Agreement.

"Our analysis shows that the goal of 2 degrees is very much a best-case scenario," said lead author Adrian Raftery, a UW professor of statistics and sociology. "It is achievable, but only with major, sustained effort on all fronts over the next 80 years."

The new, statistically-based projections, published July 31 in Nature Climate Change, show a 90 percent chance that temperatures will increase this century by 2.0 to 4.9 C.

"Our analysis is compatible with previous estimates, but it finds that the most optimistic projections are unlikely to happen," Raftery said. "We're closer to the margin than we think."

The most recent report from the Intergovernmental Panel on Climate Change included future warming rates based on four scenarios for future carbon emissions. The scenarios ranged from "business-as-usual" emissions from growing economies, to serious worldwide efforts to transition away from fossil fuels.

"The IPCC was clear that these scenarios were not forecasts," Raftery said. "The big problem with scenarios is that you don't know how likely they are, and whether they span the full range of possibilities or are just a few examples. Scientifically, this type of storytelling approach was not fully satisfying."

The new paper focuses instead on three quantities that underpin the scenarios for future emissions: total world population, gross domestic product per person and the amount of carbon emitted for each dollar of economic activity, known as carbon intensity.

Using statistical projections for each of these three quantities based on 50 years of past data in countries around the world, the study finds a median value of 3.2 C (5.8 F) warming by 2100, and a 90 percent chance that warming this century will fall between 2.0 to 4.9 C (3.6 to 8.8 F).

"Countries argued for the 1.5 C target because of the severe impacts on their livelihoods that would result from exceeding that threshold. Indeed, damages from heat extremes, drought, extreme weather and sea level rise will be much more severe if 2 C or higher temperature rise is allowed," said co-author Dargan Frierson, a UW associate professor of atmospheric sciences. "Our results show that an abrupt change of course is needed to achieve these goals."

Raftery previously worked on United Nations projections for future world population. His 2014 study used Bayesian statistics, a common tool used in modern statistics, to show that world population is unlikely to stabilize this century. The planet likely will reach 11 billion people by 2100.

In the new study, Raftery expected to find that higher populations would increase the projections for global warming. Instead, he was surprised to learn that population has a fairly small impact. That is because most of the population increase will be in Africa, which uses few fossil fuels.

What matters more for future warming is the carbon intensity, the amount of carbon emissions produced for each dollar of economic activity. That value has dropped in recent decades as countries boost efficiency and enact standards to reduce carbon emissions. How quickly that value drops in future decades will be crucial for determining future warming.

The study finds a wide range of possible values of carbon intensity over future decades, depending on technological progress and countries' commitments to implementing changes.

"Overall, the goals expressed in the Paris Agreement are ambitious but realistic," Raftery said. "The bad news is they are unlikely to be enough to achieve the target of keeping warming at or below 1.5 degrees."
-end-
The research was funded by the National Institutes of Health. Other co-authors are Alec Zimmer, a UW graduate now at Upstart Networks in Palo Alto, California; Richard Startz, a UW professor emeritus of economics who now holds a position at the University of California, Santa Barbara; and Peiran Liu, a UW doctoral student in statistics.

For more information, contact Raftery at 206-543-4505 or raftery@uw.edu and Frierson at 206-685-7364 or dargan@uw.edu. Note: Raftery is in Italy and is best reached via email.

University of Washington

Related Emissions Articles from Brightsurf:

Multinationals' supply chains account for a fifth of global emissions
A fifth of carbon dioxide emissions come from multinational companies' global supply chains, according to a new study led by UCL and Tianjin University that shows the scope of multinationals' influence on climate change.

A new way of modulating color emissions from transparent films
Transparent luminescent materials have several applications; but so far, few multicolor light-emitting solid transparent materials exist in which the color of emission is tunable.

Can sunlight convert emissions into useful materials?
A team of researchers at the USC Viterbi School of Engineering has designed a method to break CO2 apart and convert the greenhouse gas into useful materials like fuels or consumer products ranging from pharmaceuticals to polymers.

Methane: emissions increase and it's not a good news
It is the second greenhouse gas with even a global warming potential larger than CO2.

Tracking fossil fuel emissions with carbon-14
Researchers from NOAA and the University of Colorado have devised a breakthrough method for estimating national emissions of carbon dioxide from fossil fuels using ambient air samples and a well-known isotope of carbon that scientists have relied on for decades to date archaeological sites.

COVID-19 puts brakes on global emissions
Carbon dioxide emissions from fossil fuel sources reached a maximum daily decline of 17 per cent in April as a result of drastic decline in energy demand that have occurred during the COVID-19 pandemic.

Egregious emissions
Call them 'super polluters' -- the handful of industrial facilities that emit unusually high levels of toxic chemical pollution year after year.

Continued CO2 emissions will impair cognition
New CU Boulder research finds that an anticipated rise in carbon dioxide concentrations in our indoor living and working spaces by the year 2100 could lead to impaired human cognition.

Capturing CO2 from trucks and reducing their emissions by 90%
Researchers at EPFL have patented a new concept that could cut trucks' CO2 emissions by almost 90%.

Big trucks, little emissions
Researchers reveal a new integrated, cost-efficient way of converting ethanol for fuel blends that can reduce greenhouse gas emissions.

Read More: Emissions News and Emissions 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.