Agriculture’s Regional Effect on Climate ─ a Short and Interesting Study by Paul C. West and Colleagues
© 2010 Peter Free
03 November 2010
Trading carbon for food by Paul C. West and colleagues
Converting land to agricultural use generally increases the amount of carbon in the atmosphere, thereby accentuating climatic warming.
Clearing natural ecosystems for crop production release CO2 into the atmosphere as stored carbon is released from vegetation biomass and soil. . .
For example, sparsely vegetated ecosystems like deserts store little carbon, whereas densely vegetated tropical forests store much more. . . .
Collectively, the effects of land use change on global greenhouse gas emissions are substantial ─ deforestation accounts for ~12-20% of worldwide annual emissions.
© 2010 Paul C. West et al., Trading carbon for food: Global comparison of carbon stocks vs. crop yields on agricultural land, PNAS, doi:10.1073/pnas.1011078107 (online early release, 01 November 2010) (paragraph split)
Quantifying the effects of where food is grown
Paul West and colleagues attempted to comparatively quantify this effect by examining different natural and agricultural ecologies sprinkled across the planet.
For example, they asked, where does agricultural conversion of land contribute least to increased atmospheric carbon load, and where most?
They concluded that land conversion, per hectare, in the tropics resulted in nearly twice as much carbon release as similar conversions on temperate region land.
If the ratio is calculated per unit of achieved crop yield, the difference becomes nearly three-fold. This is because tropical agricultural land (as opposed to the tropics’ natural ecosystems) is less agriculturally productive than temperate zone land.
Why this finding matters
The authors estimate that the world’s increasing population, combined with elevated meat and biofuel requirements, will require a 50 percent increase in crop production by the year 2050.
Most of the approximately 100 to 200 million hectares of agricultural increase will be in the tropics.
From the atmosphere’s perspective, converting the tropics’ natural ecosystems ─ which are the planet’s most massive and densely-efficient carbon stores ─ into the world’s effectively least efficient agricultural land is problematic.
Even the best tropical case is worrying
The paper notes that, even if tropical land food production is doubled to match temperate zone production yields, tropical carbon losses will still significantly exceed those in temperate zones (~35 versus ~27 carbon tons lost per acre).
What to do?
The authors believe their findings corroborate recommendations that seek to concentrate reforestation in the tropics.
Social complexity will interfere
Obviously people in the tropics are going to have the major say on this. I can’t see them starving themselves to death for the planet’s benefit.
Though futurists envision the temperate zone making payments to the tropical (to encourage forestation), I have difficulty envisioning how that is going work. Especially given the developed world’s seeming inability to control even its own carbon emissions.
There’s another problem, too. The “payments from rich to poor” plan seems to assume that temperate zone will regularly be shipping food to the tropical region. Whether that solution is more carbon-efficient than raising tropical food remains to be assessed.
The overall problem is what it always has been ─ arguably too many us on a too-small planet
But nobody wants to talk about that.