Global carbon emissions rise, but at a slower rate

Global emissions of carbon dioxide are projected to reach a new record in 2019, although the rate of increase is expected to slow, according to a forecast released 3 December by two UK universities and the Global Carbon Project (GCP), an international research collaboration. The study’s researchers tie the smaller increase chiefly to the reduced use of coal in the US and European Union, leading to a 0.9% decline in global emissions from coal. Slowing economic growth worldwide has also helped keep the year-to-year gain in check. Still, CO₂ emissions from natural gas and oil are projected to increase 2.6% and 0.9%, respectively.

The study , published in Earth System Science Data, pegs CO₂ emissions in 2019 from human activities—including both fossil-fuel combustion and land-use changes such as deforestation—at about 43.1 billion metric tons. The uncertainty range of 39.9 billion to 46.3 billion metric tons leaves open the possibility of a small decrease in emissions from 2018 or an increase of up to 1.5%. The scientific collaboration’s annual projections tend to come close to actual emission figures. The University of East Anglia and University of Exeter worked with the GCP on the research and also published papers in Nature Climate Change and Environmental Research Letters .

The release of the forecast came as delegates from nearly 200 nations met in Madrid at the 25th session of the United Nation’s Conference of the Parties, where the Trump administration gave official notice of its intent to withdraw next year from the landmark 2016 Paris Agreement. A bleak assessment released by the UN’s Environment Programme last month warned that nations need to up their emissions-reduction pledges by a factor of five to have any hope of limiting the global temperature increase to 1.5 °C above preindustrial levels, the goal set in Paris. Staying below a 2 °C increase, the threshold beyond which scientists say the worst effects of climate change will begin to take hold, will require a threefold increase in national commitments.

Scientists cautioned against reading too much into the slowing growth projected for 2019, noting that year-to-year fluctuations have occurred in the past. For example, following two years of slight declines, emissions rose 2.1% in 2018 to set a new record. “I’m not ready to call it a trend,” says Rob Jackson, an Earth system scientist at Stanford University and a lead author of the study.

India’s emissions are projected to grow by 1.8% from 2018, and the country’s total would be higher if not for a slowing economy and heavy monsoon rains that flooded coal mines while boosting hydropower generation. China’s emissions are expected to surge by 2.6%. Although the country’s electricity generation from coal has stayed flat, coal usage has grown for the manufacturing of cement, steel, and other energy-intensive products. The Chinese government is providing incentives for new gas plants even as the nation continues to build coal plants to encourage economic growth. The government recently terminated or reduced subsidies that had been driving rapid growth of wind and solar power.

“We’re still on the accelerator, and our goal isn’t to keep emissions constant—it’s to drive them to zero,” says Klaus Lackner, director of the Center for Negative Carbon Emissions at Arizona State University, who wasn’t involved in the study.

Emissions in the US and the EU are predicted to fall by 1.7% in 2019, as coal consumption for each drops by 10%. Coal emissions have been halved over the past 15 years in the US, says Jackson. A sharp rise in the price of carbon in the EU’s emissions trading scheme and other policies have also contributed to the reduction, the report says. (For more on emissions trading schemes, see Physics Today, December 2019, page 28 .)

The strongest trend seen in the data, Jackson says, is the increase in carbon emissions from natural gas, which are estimated to jump by 3.5% in the US and 2.6% worldwide. Although natural gas emits roughly half as much CO₂ as coal per unit of energy, Lackner notes that the new natural gas–fired plants that are supplanting coal will operate for decades.

Lackner figures that the world must reduce its carbon intensity, measured by unit of energy or by GDP, by more than 9% each year to keep the atmospheric CO₂ concentration below 450 parts per million, a widely recognized ceiling for limiting the global temperature increase to 2 °C. Achieving that would require a level of societal mobilization comparable to that of World War II, he says. And should action be delayed until 2025, the annual cuts needed will grow to 14%. If emissions remain constant, the 450 ppm threshold will be breached in 15 years, Lackner says.

The average atmospheric CO₂ concentration for the month of November 2019 was nearly 411 ppm, as measured by NOAA at the Mauna Loa Observatory in Hawaii. That’s a roughly 2 ppm increase from a year ago and 10 ppm above the November 2015 average. Since preindustrial times, atmospheric CO₂ concentrations have risen by 47%.