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‘Abrupt Increase’ In CO2 Absorption Stuns Scientists

Scientists have discovered that plants, trees and soil have abruptly increased their atmospheric carbon dioxide intake in the last 20 years. The land biosphere was taking in about one billion tonnes of carbon per year since 1988, equal to about 10 per cent of the global fossil fuel emissions for 2010. “We were completely taken by surprise by the findings. It’s opened up a whole new series of questions.”

The earth would have warmed faster in the last two decades had there not been an unexplained rise in the amount of carbon dioxide being absorbed on land, scientists believe.

Scientists have discovered an “abrupt increase” since 1988 in the uptake of carbon dioxide (CO2) by the land biosphere, which comprises all of the planet’s plant and animal ecosystems.

Wellington-based scientist Dr Sara Mikaloff-Fletcher, from the National Institute of Water and Atmospheric Research, was part of the global research team investigating the distribution of CO2 emissions.

Ms Mikaloff-Fletcher said the breakthrough had taken scientists “completely by surprise”.

Although the findings were interesting, she said they created more questions than answers.

“We applied some really exciting statistical techniques … to look at how (the uptake of CO2 on land) is changing over time.

“We were completely taken by surprise (by the findings). It’s opened up a whole new series of questions.”

The findings do not contradict existing science about global warming, but rather explain how much CO2 is absorbed by plants and animals, with some of the CO2 then being passed from plants into the land.

A report into the findings says the increase in uptake is “a big number”, about one billion tonnes of carbon per year.

“To put it into context, that is over 10 per cent of global fossil fuel emissions for 2010,” the report said.

Applying the new statistical approach to records from as early as the 1950s, the “sharp increase” in 1988 has continued to the present day.

Ms Mikaloff-Fletcher said there had been some theories about what had caused the increased uptake by the land, but so far no answer has been found.

“What it does mean is that the climate change has been a lot slower than it would have been otherwise (because) less of the CO2 we’re producing is staying in the atmosphere.”

Ms Mikaloff-Fletcher said scientists were now trying to establish what caused the increase in CO2 being absorbed by the land and whether that might change in the future.

“While the increase was shown to be significant, the physical processes driving it remain a mystery. It poses big questions for us. What caused this shift? What can it tell us about how land’s ability to take up CO2 is going to change in the future? How is that going to feed back into climate conditions in the future?”

New Zealand Herald, 11 July 2012

see also:

The Global Land Carbon Sink

Gurney, K.R. and Eckels, W.J. 2011. Regional trends in terrestrial carbon exchange and their seasonal signatures. Tellus 63B: 328-339.

According to Gurney and Eckels (2011), “projections of atmospheric CO2 concentrations and the resulting climate change rely to a significant degree on projections about future land and ocean uptake,” and citing the work of Friedlingstein et al. (2006) and Sitch et al. (2008), the two authors proceeded to investigate how CO2 uptake by earth’s terrestrial surfaces has varied over the past three decades. In doing so, the Gurney and Eckles utilized the results of atmospheric CO2 inversions — constrained by observed atmospheric CO2 concentrations (Tans et al., 1990) and simulated atmospheric transport — to estimate trends in air-to-land carbon fluxes, as per Enting (2002). This they did, as they describe it, “at spatial scales down to the continents using the results of the TransCom 3 international atmospheric CO2 inversion inter-comparison (Gurney et al., 2002, 2008),” which effort involved 13 participating modeling groups. So what did they learn?

The two U.S. researchers report that the results of their analyses indicate that the global land carbon sink is intensifying, and that it is doing so at a rate of 0.057 PgC/year/year, resulting in 1.65 PgC of additional uptake over the period examined (1980-2008), which finding, in their words, “is consistent with related findings in recent years,” citing in this regard the studies of Cao et al. (2002), Cao et al. (2005), Le Quere et al. (2009) and Piao et al. (2009).

As ever more anthropogenic CO2 is emitted into the atmosphere and the air’s CO2 concentration rises ever higher, so too does the photosynthetic prowess of earth’s terrestrial vegetation grow ever stronger, as the great global greening of the earth gains ever more momentum and sucks ever more CO2 out of the air and incorporates it into living biomass and soil organic matter, thereby muting the rate of global warming that would otherwise prevail in the absence of this important negative feedback phenomenon.

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