The Western Hemisphere seen from space
From forests to soils to coastal waters to the atmosphere, carbon is literally all around us. A new report maps its path around North America and explores the fate of the carbon cycle as fossil fuels continue to burn. Credit: NASA/NOAA/GSFC/Suomi NPP/VIIRS/Norman Kuring

The same day that the National Climate Assessment was released last month, a different report was quietly released by its side: the Second State of the Carbon Cycle Report. The report tracks carbon as it moves through ecosystems, from forests to cities to coastal waters and more, and the report serves as the most comprehensive evaluation of carbon cycle science in North America for the past decade.

“Carbon is the basis of life on Earth,” Gyami Shrestha, director of the U.S. Carbon Cycle Science Program and an editor of the report, told Eos. “When it binds with oxygen, hydrogen and nutrients, it creates the basis of all living beings on Earth, and it’s essential for human activities.”

“It’s important to know how we are impacting Earth, and how the carbon cycle is impacting Earth.”

Additionally, said Shrestha, humans are affecting the carbon cycle by burning fossil fuels, and the report seeks to pinpoint humans’ fingerprint in the present and in years to come.

“Carbon is very critical in regulating climate,” Shrestha said. “It’s important to know how we are impacting Earth, and how the carbon cycle is impacting Earth.”

The report, the second iteration published by the intergovernmental U.S. Global Change Research Program, includes research since 2007 across the United States, Mexico, and Canada. More than 200 scientists from across research institutions, national laboratories, government agencies, universities, and the private sector served as authors, pulling from research spanning more than 3,000 publications. The result is a comprehensive assessment of carbon cycling in land, air, and water in North America.

Here are some of the main findings from the more than 900-page report:

  1. Since the industrial revolution, carbon dioxide (CO2) has increased in our atmosphere by 40%. Methane concentrations have skyrocketed in the same time period, increasing by 160% in our atmosphere.
  2. North America reduced its global fossil fuel emissions from 24% to 17% in the time span between 2004 and 2013. Industries switching energy sources to natural gas instead of coal and improvements in vehicle efficiency largely explain the drop, as does the increase in emissions from other continents.
  3. Forests, grasslands, and other land ecosystems have been sucking up carbon to the tune of 600–700 teragrams of carbon per year in North America (for scale, that’s about a third of the continent’s annual fossil fuel emissions).
  4. The data on how much carbon our coastal waters take in and lock away still have large uncertainties. But researchers did highlight how much gets absorbed by certain ecosystems, such as tidal wetlands and estuaries, which suck up 17 teragrams of carbon per year and bury the majority in their sediments.
  5. Although methane continues to build up in our skies globally, North America is not increasing its emission rates, even though it has been amping up natural gas use.
  6. Cutting emissions of greenhouse gases (GHGs) in North America by 80% of 2005 levels will cost $1–4 trillion from 2015 to 2050. The number may pale in comparison to how much climate damage could cost in the future. By 2050, for instance, the bill for climate change damages may amount to $170–206 billion in that year alone.
  7. Urban areas in North America burp out the most carbon of any locations, yet those sources are among the hardest to track.
  8. Frozen soil in the Arctic is melting and could release 5%–15% of its carbon stores by the end of this century.
  9. The waters off Oahu, the Aleutian Islands, and the Gulf of Maine are acidifying, and the low pH is already altering ecosystems.

The report sees some paths forward: “Recently, many U.S. states, led by their governors, have made state-level commitments to reduce GHG emissions,” the authors wrote in the report’s executive summary.

In addition, scientists should work toward resolving open questions, including how CO2 feedbacks could tweak terrestrial ecosystems and how humans are precisely shaking up the carbon cycle. More research, says the report, is yet to come.

“The U.S. has been able to decrease its emissions. But it’s not been enough.”

Still, the authors behind the fourth edition of the National Climate Assessment (NCA4) wrote in Eos that current global and regional efforts to mitigate the causes of climate change are not drastic enough to avoid “substantial damages to the U.S. economy, environment, and human health and well-being over the coming decades.”

“Instead, more immediate and substantial global greenhouse gas emissions reductions and more regional adaptation efforts would be needed to avoid the most severe consequences in the long term,” the NCA4 authors wrote.

Shrestha agrees, reminding us that the United States contributes the majority of emissions for North America.

“The U.S. has been able to decrease its emissions,” Shrestha said of the past decade. “But it’s not been enough.”

—Jenessa Duncombe (@jenessaduncombe), News Writing and Production Intern


Duncombe, J. (2018), Tracing the path of carbon in North America, Eos, 99, Published on 04 December 2018.

Text © 2018. The authors. CC BY-NC-ND 3.0
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