Greening the Planet: The Fertilizer Effect of CO2 Slows Warming

By Pat Joseph

A new study led by UC Berkeley Lab researcher Trevor Keenan suggests that increased plant growth is slowing the accumulation of carbon dioxide in the atmosphere, a finding that could help explain the mystery of why the uptick in CO2 concentrations has leveled off since 2002, even as emissions have increased. “We believed one of the planet’s main carbon sinks had unexpectedly strengthened,” Keenan explained in a Lab press release. “The question was: which one?”

Sinks are what climate scientists call mechanisms that remove carbon from the atmosphere. The ocean is one such sink, and it has absorbed more carbon in recent years, but at a steadily increasing rate. Terrestrial ecosystems are more variable. Using computer models, satellite measurements, and ground-based networks, researchers zeroed in on the fertilizer effect of CO2 and the resulting increase in photosynthesis as the most plausible explanation for the observed slow-down in CO2 concentrations.

This sounds like good news: The planet is getting greener while global warming slows. But it comes with worrying caveats. For starters, the effect may not last as increased temperatures dampen plant growth and rainfall patterns change. Also, much of the greening has occurred in cold regions previously blanketed in snow. And while snow and ice reflect solar energy away from the planet, vegetation absorbs it, increasing land surface temperatures. Finally, the effect is simply too small to keep up with emissions. “Unfortunately,” says Keenan, the increased carbon uptake by plants “is nowhere near enough to stop climate change.”

The study, published in November in Nature Communications, concludes, “Without effective reduction of global CO2 emissions, … future climate change remains a stark reality.”

A new study led by Berkeley Lab researcher Trevor Keenan suggests that increased plant growth is slowing the accumulation of carbon dioxide in the atmosphere, a finding that could help explain the mystery of why the uptick in CO2 concentrations has leveled off since 2002, even as emissions have increased. “We believed one of the planet’s main carbon sinks had unexpectedly strengthened,” Keenan explained in a Lab press release. “The question was: which one?”

Sinks are what climate scientists call mechanisms that remove carbon from the atmosphere. The ocean is one such sink, and it too has absorbed more carbon in recent years, but at a steadily increasing rate. Terrestrial ecosystems are more variable. Using computer models, satellite measurements, and ground-based networks, researchers zeroed in on the fertilizer effect of CO2 and the resulting increase in photosynthesis as the most plausible explanation for the observed slow-down in CO2 concentrations.

This sounds like good news: The planet is getting greener while global warming slows. But it comes with worrying caveats. For starters, the effect may not last as increased temperatures dampen plant growth and rainfall patterns change. Also, much of the greening has occurred in cold regions previously blanketed in snow. And while snow and ice reflect solar energy away from the planet, vegetation absorbs it, increasing land surface temperatures. Finally, the effect is simply too small to keep up with emissions. “Unfortunately,” says Keenan, the increased carbon uptake by plants “is nowhere near enough to stop climate change.”

The study, published in November in Nature Communications, concludes, “Without effective reduction of global CO2 emissions, … future climate change remains a stark reality.”

A new study led by UC Berkeley Lab researcher Trevor Keenan suggests that increased plant growth is slowing the accumulation of carbon dioxide in the atmosphere, a finding that could help explain the mystery of why the uptick in CO2 concentrations has leveled off since 2002, even as emissions have increased. “We believed one of the planet’s main carbon sinks had unexpectedly strengthened,” Keenan explained in a Lab press release. “The question was: which one?”

Sinks are what climate scientists call mechanisms that remove carbon from the atmosphere. The ocean is one such sink, and it too has absorbed more carbon in recent years, but at a steadily increasing rate. Terrestrial ecosystems are more variable. Using computer models, satellite measurements, and ground-based networks, researchers zeroed in on the fertilizer effect of CO2 and the resulting increase in photosynthesis as the most plausible explanation for the observed slow-down in CO2 concentrations.

This sounds like good news: The planet is getting greener while global warming slows. But it comes with worrying caveats. For starters, the effect may not last as increased temperatures dampen plant growth and rainfall patterns change. Also, much of the greening has occurred in cold regions previously blanketed in snow. And while snow and ice reflect solar energy away from the planet, vegetation absorbs it, increasing land surface temperatures. Finally, the effect is simply too small to keep up with emissions. “Unfortunately,” says Keenan, the increased carbon uptake by plants “is nowhere near enough to stop climate change.”

The study, published in November in Nature Communications, concludes, “Without effective reduction of global CO2 emissions, … future climate change remains a stark reality.”

A new study led by Berkeley Lab researcher Trevor Keenan suggests that increased plant growth is slowing the accumulation of carbon dioxide in the atmosphere, a finding that could help explain the mystery of why the uptick in CO2 concentrations has leveled off since 2002, even as emissions have increased. “We believed one of the planet’s main carbon sinks had unexpectedly strengthened,” Keenan explained in a Lab press release. “The question was: which one?”

Sinks are what climate scientists call mechanisms that remove carbon from the atmosphere. The ocean is one such sink, and it too has absorbed more carbon in recent years, but at a steadily increasing rate. Terrestrial ecosystems are more variable. Using computer models, satellite measurements, and ground-based networks, researchers zeroed in on the fertilizer effect of CO2 and the resulting increase in photosynthesis as the most plausible explanation for the observed slow-down in CO2 concentrations.

This sounds like good news: The planet is getting greener while global warming slows. But it comes with worrying caveats. For starters, the effect may not last as increased temperatures dampen plant growth and rainfall patterns change. Also, much of the greening has occurred in cold regions previously blanketed in snow. And while snow and ice reflect solar energy away from the planet, vegetation absorbs it, increasing land surface temperatures. Finally, the effect is simply too small to keep up with emissions. “Unfortunately,” says Keenan, the increased carbon uptake by plants “is nowhere near enough to stop climate change.”

The study, published in November in Nature Communications, concludes, “Without effective reduction of global CO2 emissions, … future climate change remains a stark reality.”

From the Winter 2016 Reality Bites issue of California.
Image source: Detail of map, courtesy of NASA.
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Comments

CO2 is a by-product of the burning of fossil fuels. The heat released is the real cause of global warming. The conversion of CO2 and H2O to organic matter through photosynthesis, does absorb some solar energy but too much heat is produced from natural gas, even if all the CO2 were immediately converted to organic matter, and total heat from nuclear plants, which has no mitigating CO2, is three times the electrical output. Conversion of CO2 is occurring at a slower pace than it is being produced. The heat produced by the consumption of the acknowledged energy sources alone, is more than four times the amount attributable to the rise in air temperature. Do not be concerned with the CO2. When renewable energy sources replace fossil and nuclear, the only question will be “has the reflected heat decreased enough due to melting of snow and ice to prevent the reversal of global warming”.
Dear Philip, thanks for your comment. The idea that so-called ‘waste heat’ is the leading cause of global warming is interesting, but not supported by the scientific consensus on climate change. It does have an effect but a relatively small one compared to greenhouse forcing. See: http://www.cgd.ucar.edu/tss/ahf/ Thanks again.

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