Washington — The planet’s capacity to absorb carbon emissions is almost keeping pace with the increasing amount of greenhouse gases (GHGs) spewed into the atmosphere by human activities. But that won’t last forever, scientists say, in findings published August 1 in the journal Nature.
Scientists from the National Oceanic and Atmospheric Administration (NOAA) and the University of Colorado collaborated to analyze 50 years' worth of global carbon dioxide (CO2) measurements. They found that the planet’s oceans, forests and other ecosystems have not yet reached their capacity to absorb GHGs.
“Globally, these carbon dioxide ‘sinks’ have roughly kept pace with emissions from human activities, continuing to draw about half of the emitted CO2 back out of the atmosphere,” said NOAA’s climate researcher Pieter Tans. “However, we do not expect this to continue indefinitely.”
Tans, based at NOAA’s Earth System Research Laboratory in Colorado, co-authored the study with lead author Ashley Ballantyne of the University of Colorado.
Carbon emissions not absorbed by Earth’s natural processes accumulate in the atmosphere, where scientists say they contribute to global warming.
The oceans and forests that absorb carbon are known as “carbon sinks” — natural or artificial pools where carbon is stored for an indefinite period. Plants consume carbon dioxide in photosynthesis, and the oceans take up carbon in particle form and by absorption of CO2 in a gaseous form.
GHGs have increased substantially over the half-century span of the data examined by these scientists.
“Earth is taking up twice as much CO2 today as it was 50 years ago,” Ballantyne said.
A press release from NOAA says this analysis makes it clear that not enough is yet understood about the processes by which ecosystems of the world remove CO2 from the atmosphere.
Cultivating forests to absorb excess GHGs has been proposed as a response to global warming, but whether such projects would act as effective sinks is not really known.
“Since we don’t know who or where this process is happening, we cannot count on it,” Tans said. “We need to identify what’s going on here, so that we can improve our projections of future CO2 levels and how climate change will progress in the future.”
The absorption capacity of Earth’s carbon sinks is expected to slow down. Increased ocean acidity is already occurring due to carbon absorption, and “We know it becomes harder to stuff even more CO2 into the oceans,” Tans said.
The 50 years of data reviewed in the study had been collected by NOAA and the Scripps Institution of Oceanography from remote sites around the world, including the top of a mountain in Hawaii and the South Pole.