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Research Highlight

Global Carbon Budget: Fossil fuel emissions and atmospheric CO2 on the rise

Topics: Clean Energy Climate and Environmental Systems

Global carbon emissions are on the rise again after three years of little growth. Emissions from fossil fuels are projected to rise 2% in 2017 to an all-time high driven largely by increased fossil fuel consumption in China and India according to the recently released Global Carbon Budget. The upward trend represents a return to the growth rates seen during 2004-2013.

The background level of atmospheric carbon dioxide (CO2) in the troposphere, a key contributor to climate change, is expected to increase by 2.5 parts per million (ppm) in 2017, reaching a new high of more than 405 ppm.

The Global Carbon Budget 2017, an annual release from the Global Carbon Project (GCP), offers updated estimates of the major sources and sinks of carbon and provides information about the status of emissions around the world and the human activities that are influencing the upward trend.

The report indicates fossil fuel emissions from China, projected to increase 3.5% based on a burgeoning economy and growing coal, oil, and gas consumption, are the primary driver for the projected global rise. Declines in emissions in the US and EU are projected to be smaller than those of the last decade at 0.4% and 0.2%, respectively.

The budget also revealed renewable energy growth and energy efficiency improvements, as detailed in a related article in the journal Earth System Science Data.

Living data and new analyses reduce uncertainty

More than 70 researchers around the world collaborated on the Global Carbon Budget 2017, which brings together quantitative measurements and sophisticated models to assess anthropogenic CO2 emissions and their redistribution among the atmosphere, ocean, and terrestrial biosphere.

With fossil fuels contributing the majority of carbon emissions—88% in the last decade—the accuracy of that component is critical to the budget. That’s where ORNL’s Tom Boden comes in.

Boden and his former ORNL colleagues Gregg Marland and Bob Andres developed a methodology for quantifying fossil fuel carbon emissions in the 1980s and 1990s, and Boden continues to employ the methods today. The data Boden analyzes includes energy statistics from all countries and stretches back to the dawn of the industrial revolution in 1750, making for a uniquely inclusive and consistent record.

Rather than adding a single year of data to a static set, Boden stresses that the GCP report is based on “living” data that is continually collected and updated with new scientific findings.

“Our data are getting better, more diverse, and more robust,” said Boden. “The models are richer, and this year’s report has the most exhaustive characterization of uncertainty that I’ve seen for each of the five key pillars.”

The terrestrial pillar was calculated with increased scientific rigor this year. Previously, the land sink was determined by assigning the residual after the other pillars—atmosphere, ocean, fossil fuel emissions, and land-use change—had been assessed. For the 2017 budget, a team of more than 20 international scientists, including ORNL’s Anthony Walker, used a suite of models to determine the terrestrial sink.

With the added precision in the land sink calculation, the average budget imbalance for the past decade decreased to 0.6 gigatonnes of carbon. The imbalance, which indicates overestimated emissions and/or underestimated sinks, continues to decline as scientific data and models improve.

“The report is a commendable scientific effort to properly understand what we know, what we don’t know, and explain that in a very open fashion,” said Walker.

Taking the pulse of the planet with this tenth GCP budget and fifth consecutive journal publication provides a big picture perspective and contributes new information to the ongoing discussion about climate change.

“One of the big questions,” said Boden, “is how good are these numbers? In this latest release we’ve addressed this question and noted the uncertainties, and most are within 5%.”