Emissions Must Fall By Mid-Century to Meet Paris Temperature Goals, Study Finds
With the exception of the U.S., every country in the world has now expressed an intention to honor the Paris agreement, which means they have all committed to limiting global warming to well below 2 degrees Celsius above pre-industrial levels and to achieving net zero greenhouse gas emissions by the second half of the current century.
Now, two studies published Monday provide insight into how those commitments to avoid dangerous levels of climate change might practically be fulfilled.
One study, published in Nature Climate Change, used models to look specifically at the relationship between the Paris agreement's temperature and emissions goals, and concluded they are not always consistent: Temperature goals would best be achieved by reducing emissions as early and steeply as possible, and reaching zero emissions too late might render them out of reach.
Another study published in Nature Energy offered one small but concrete step in that direction of a speedy emissions reduction. If countries used natural gas instead of coal in existing power stations, they could reduce global greenhouse gas emissions by 3 percent in less than five years.
The first study, which was led by Katsumasa Tanaka of the National Institute for Environmental Studies in Japan and co-authored by National Center for Atmospheric Research (NACAR) senior scientist Brian O'Neill, ran 10 different models for different temperature and emissions scenarios, NCAR's AtmosNews reported Monday.
The results revealed that we could limit warming to 1.5 degrees Celsius by reducing emissions by 80 percent by 2033 or 2 degrees by reducing emissions by two-thirds by 2060. Emissions could then level off without having to fall all the way to zero.
However, if we overshoot the temperature goals and then try to double back to 1.5 or 2 degrees by the end of the century, it will not be enough to reduce emissions to zero; we will have to devise ways to remove carbon dioxide from the atmosphere.
"What we found is that the two goals do not always go hand in hand," Tanaka told AtmosNews."If we meet temperature targets without first overshooting them, we don't have to reduce greenhouse gas emissions to zero. But if we do reduce emissions to zero, we still might not meet the temperature targets if we don't reduce emissions quickly enough."
The study underscores the importance of timing. It found that temperature will not rise above 2 degrees if we reach zero emissions by 2060, but, if we delay until the end of the century, temperatures will rise above 2 degrees by 2043 and remain above 2 degrees for at least a century.
O'Neil and Tanaka told AtmosNews they thought their research might inform the "global stocktakes" that countries must make every five years under the Paris agreement, reporting their progress and altering their goals.
"Our study and others may help provide countries with a clearer understanding of what work needs to be done to meet the goals laid out in the agreement. We believe that the Paris Agreement needs this level of scientific interpretation," Tanaka said.
The Nature Energy study offered one step countries could take to begin reducing emissions quickly. The study, a joint effort by Imperial College London and the University of Sheffield, found that the UK reduced its total carbon emissions by 6 percent in 2016 by switching the fuel source of power plants from coal to natural gas, which emits less than half of the carbon dioxide that coal does when burned.
According to an Imperial College London press release, the study asked if the UK's success could be replicated in the 30 largest coal-burning countries. It found that, if these countries used existing infrastructure and capabilities to switch from coal to gas, they could reduce global carbon dioxide emissions by 0.8 to 1.2 gigatonnes a year.
The study's authors were quick to point out that switching to gas was a stop-gap measure for reducing emissions as quickly as possible while newer, more sustainable technologies are developed.
"Switching from coal to gas is not a long-term solution, but it is an important step to start reducing emissions quickly and at minimal cost. This will give us time to build up the required renewable energy capacity to permanently cut global carbon emissions," co-author and Imperial College London researcher Dr. Iain Staffell said in the release.
And, as O'brien and Tanaka's research indicates, time is of the essence.