Global Carbon Budget: Fossil fuel CO2 emissions growth nearly flat; atmospheric concentration continues to rise
The latest annual Global Carbon Budget shows the growth of carbon dioxide (CO2) emissions from fossil fuel use is likely to be nearly flat for the third year in a row, with fewer emissions from coal burning a possible factor. Even with that slowdown, however, atmospheric CO2 continues to climb—growing by a record high of 23 gigatonnes (Gt) in 2015 and projected to grow 25 Gt in 2016.
The Global Carbon Budget 2016, an annual release from the Global Carbon Project (GCP), shows that CO2 emissions from fossil fuel combustion, gas flaring, and cement production have leveled off since 2014 and the emissions growth rate has slowed over the past decade. The latest budget predicts global CO2 emissions growth from fossil fuels and cement production will continue to be low in 2016, gaining only 0.2% from 2015. The budget also shows that decadal average growth was 1.8% a year from 2006 through 2015 compared with 3.5% from 2000 through 2009.
Corinne Le Quéré, director of the Tyndall Centre at the University of East Anglia, who led the data analysis, said, “This third year of almost no growth in emissions is unprecedented at a time of strong economic growth. This is a great help for tackling climate change but it is not enough. Global emissions now need to decrease rapidly, not just stop growing.”
Carbon emissions from the world’s two largest fossil-fuel consumers, China and the United States, were lower. US emissions declined by 2.6% in 2015, with coal decreasing and oil and gas increasing. US fossil fuel emissions are expected to decrease by 1.7% in 2016. China’s emissions fell 0.7% in 2015 and are expected to decline by 0.5% in 2016.
Some US coal burning may have been replaced by natural gas from hydraulically fractured wells, and data indicate that China may be burning some lower-emitting coal as well, noted researchers involved in the project at Oak Ridge National Laboratory.
Although minimal growth is projected for 2016, fossil fuel CO2 emissions remain at an all-time high, with the estimate for 2016 at 36.4 Gt CO2 (or 9.9 Gt carbon), which continues to increase atmospheric CO2 concentrations, according to the budget released November 14 and detailed in a related article in the journal Earth System Science Data.
Budget pulls together measurements, statistics, modeling analysis
It’s too early to say whether fossil fuel emissions growth will stay flat in coming years, said Tom Boden of ORNL’s Carbon Dioxide Information Analysis Center and a key contributor to GCP’s annual budget.
“At the same time that coal use is down in the US, we’re exporting record amounts of coal to Europe,” Boden noted. “There are always factors that you can’t foresee, and that’s why we don’t like to predict emissions more than a couple of years out.
“Too many times there have been abrupt changes that could affect global and national energy use and corresponding emissions,” including everything from mine strikes to war to the global financial crisis and even political changes, Boden said.
The report, pulled together by 60 researchers from around the globe, has been published yearly since 2005, with human emissions from fossil-fuel use and land-use changes divided among the atmosphere, land, and ocean. The budget brings together measurements, statistical information, and analyses of model results to provide an assessment of the global carbon budget and uncertainties from 1959 to 2016.
“It is important to realize how the GCP budget is derived and that it simplifies the global carbon budget into five fundamental pieces—releases from land use changes and fossil fuel usage (the two big human impacts), the atmospheric reservoir, and the ocean and terrestrial sinks,” Boden explained. “The atmospheric part we know well based on high-precision measurements worldwide. Fossil fuel emissions are based on actual energy production, trade, and fuel chemistry data. Land-use change emissions and oceanic uptake are based on both historical measurements and model results. The fifth piece, uptake by the terrestrial biosphere, is simply the residual necessary to balance the sum of sources and sinks.”
Atmospheric CO2 hits above 400 ppm
The concentration of CO2 in the atmosphere has grown from about 277 parts per million (ppm) in 1750, when the industrial era began, to an average of 399.4 ppm in 2015. The global monthly average of atmospheric CO2 rose above 400 ppm for the first time in May 2013 and has stayed above that monthly average since November 2015, the report noted. This is the highest level in at least 800,000 years and is 44% above pre-industrial levels, the GCP notes.
The increase in atmospheric CO2 concentration is expected to be relatively high in 2016 because of the record high emissions levels and the persistence of a smaller residual terrestrial sink. The lower sink is in response to El Niño-related weather conditions over tropical land that tend to stress plants and hamper their carbon uptake, the researchers said.
“We saw a lower land carbon sink, due to the particularly warm, El Niño-influenced weather at the end of 2015 that carried over into this year,” added Anthony Walker, an ORNL researcher who contributed modeling work to the project. “There have been several substantial El Niño years in the recent past and they are often associated with lower land carbon sink.”
“The report and approach reflect the complexity and challenges in characterizing the terrestrial uptake of carbon,” Boden said. “The terrestrial biosphere is highly variable with lots of influential factors—complex and diverse ecosystems, varied responses to weather conditions such as El Niño, different soil conditions, disease and insect outbreaks, disturbance, and on and on.”
The report itself is a “tremendous undertaking,” Walker noted, “bringing together painstakingly compiled fossil fuel emissions data, global models, and very large datasets, including satellite data, atmospheric data, and requiring simulations be run in a short timeframe and turned into a product that many researchers turn to.”
The carbon budget is used in conjunction with other climate indicators like global surface temperatures, sea level rise, and Arctic sea ice extent as key indicators of the extent of human-induced climate change.