Timothy Birdnow

The Earth is greening - and atmospheric carbon dioxide is the reason, according to climatologist Patrick Michaels.

From Climate Etc.

A new paper finds higher than expected CO₂ fertilization inferred from leaf to global observations. The paper predicts that the Earth is going to gain nearly three times as much green matter as was predicted by the IPCC AR5.

Earlier this month, I posted a short piece about an explosive paper on planetary greening that appeared in the journal Global Change Biology. I’ve since mused that it deserves a considerably longer, more contextual post.

The innocuously titled paper, "Higher than expected CO₂fertilization inferred from leaf to global observations”, by Vanessa Haverd (of Australia’s CSIRO) and eight coauthors uses a biophysical model and observed climate to back-calculate global primary productivity (GPP; the net change in standing vegetation per year), and to forward-calculate it using climate model forecasts.

Abstract. "Several lines of evidence point to an increase in the activity of the terrestrial biosphere over recent decades, impacting the global net land carbon sink (NLS) and its control on the growth of atmospheric carbon dioxide (c_a). Global terrestrial gross primary production (GPP)—the rate of carbon fixation by photosynthesis—is estimated to have risen by (31±5)% since 1900, but the relative contributions of different putative drivers to this increase are not well known. Here we identify the rising atmospheric CO₂concentration as the dominant driver. We reconcile leaf‐level and global atmospheric constraints on trends in modeled biospheric activity to reveal a global CO₂fertilization effect on photosynthesis of 30% since 1900, or 47% for a doubling ofc_aabove the pre‐industrial level. Our historic value is nearly twice as high as current estimates (17±4)% that do not use the full range of available constraints. Consequently, under a future low‐emission scenario, we project a land carbon sink (174PgC, 2006–2099) that is 57PgC larger than if a lower CO₂fertilization effect comparable with current estimates is assumed. These findings suggest a larger beneficial role of the land carbon sink in modulating future excess anthropogenic CO₂ consistent with the target of the Paris Agreement to stay below 2°C warming, and underscore the importance of preserving terrestrial carbon sinks.”

Posted by: Timothy Birdnow at 11:47 AM | Comments (4) | Add Comment
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