North American cold-climate forests are absorbing less carbon: study


By Xu Jing
  • World
  • Wednesday, 19 Aug 2020

CHICAGO, Aug. 18 (Xinhua) -- A study led by University of Michigan (UM) researchers shows that the amount of carbon Siberian forests contribute to the planet's seasonal carbon flux has increased much more than that of other forests at similar latitudes.

Since the early 1980s, the seasonal carbon uptake in Siberian forests has increased four times more than that of North American boreal forests like those in Alaska and western Canada.

To produce the findings, a research team involving experts from around the globe began with actual measurements of atmospheric CO2, collected over decades by the National Oceanic and Atmospheric Administration (NOAA).

They then worked backwards, using a computer model to calculate the regional surface emissions that would result in atmospheric carbon levels that matched the actual observations.

"We used these realistic surface fluxes and released them to the atmosphere in our model, and what's unique is that we tagged individual regions differently," said Keppel-Aleks, UM assistant professor of climate and space sciences and engineering. "We could watch red CO2 originating from Siberia, blue CO2 originating from North America, green CO2 originating from lower latitude ecosystems. That allowed us to figure out which regions are responsible for this increase in the seasonal cycle."

The varied carbon flux across different forests of similar latitudes suggests that, while some forests, like those in Siberia, are continuing to increase their carbon uptake, others, like those in North America, may not. They may even absorb less as the climate changes.

"This research shows that we need to be thinking differently about how we understand the carbon cycle," said study co-author Gretchen Keppel-Aleks, UM assistant professor of climate and space sciences and engineering. "We can't just lump ecosystems together by their latitude. We need to be thinking about individual species and specific seasonal cycles of temperature and precipitation.

The research also corroborates earlier data that shows significant greening in Siberian forests alongside much less greening at similar latitudes in North America.

"It's really significant that, using completely independent atmospheric data, we're corroborating the browning and greening trends in the remote sensing data and showing that Siberian ecosystems do in fact seem to be growing more productive in the summer," Keppel-Aleks said.

"It's another unambiguous sign that humans are causing changes in the Earth's ecosystems, and it shows that we need to develop a better understanding of those ecosystems if we want to predict what's in store for the planet," Keppel-Aleks said.

The study is the first to quantify how carbon emitted from specific surface regions during the annual carbon flux affects the seasonal cycle of CO2 in the atmosphere

The study has been published in PNAS.

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