FF vs LULCC emissions

[Govindasamy Bala]

https://doi.org/10.1088/1748-9326/ac69fd

This ERL paper demonstrating the fundamental difference between Fossil Fuel emissions and LULCC was published some months back, but I am not sure it was posted here. 

Key message: FF emissions and LULCC are fundamentally different. Hence, in terms of climate benefits, offsetting FF emissions with afforestation is scientifically flawed. 

This is textbook stuff but good to demonstrate the concept using a comprehensive Earth system model. 

https://doi.org/10.1088/1748-9326/ac69fd 

Contrasting climate and carbon-cycle consequences of fossil-fuel
use versus deforestation disturbance

Abstract
Carbon dioxide emissions from deforestation disturbance (e.g. clear-cutting, forest fires) are in the same units as carbon dioxide emissions from fossil fuels. However, if the forest is allowed to regrow, there is a large difference between the climate effects of that forest disturbance and the climate effects of fossil CO2. In this study, using a set of idealized global climate-carbon model simulations with equal amounts of CO2 emissions, we show that on century to millennial timescales the response of the climate system to fossil-fuel burning versus deforestation disturbance are vastly different. We performed two 1000-year simulations where we added abrupt emissions of about 600 PgC to the
preindustrial state as a consequence of either fossil fuel use or deforestation disturbance with vegetation regrowth. In the fossil fuel simulations, after 1000 years, about 20% of the initial atmospheric CO2 concentration perturbation remains in the atmosphere and the climate is about 1 ◦C warmer compared to the preindustrial state. In contrast, in the case of deforestation with regrowth, after 1000 years, atmospheric CO2 concentration returns close to preindustrial values, because deforested land will typically recover its carbon over the decades and centuries in the absence of further human intervention. These results highlight the differences in the degree of long-term commitment associated with fossil fuel versus deforestation emissions.

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With Best Wishes,

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G. Bala
Professor
Center for Atmospheric and Oceanic Sciences
Indian Institute of Science
Bangalore - 560 012
India

Tel: +91 80 2293 3428; +91 80 2293 2505
Fax: +91 80 2360 0865; +91 80 2293 3425
Email: gb...@iisc.ac.in; bala.gov@gmail.com
Google Scholar
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[Daniel Nepstad]

Thanks for sharing.

Your study assumes that deforestation is followed by forest regrowth, correct?  But most deforestation is followed by the establishment of permanent cropland or grazing land. This is consistent with the growing demand of the human population for food, feed and fuel from the land. And where forest is allowed to regrow, it is often subject to further disturbance (fire, logging, thinning) that prevent it from recovering pre-clearing carbon stocks.

Could you explain the rationale for assuming that all deforestation is followed by regrowth?  

Kind regards,

Dan

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[Govindasamy Bala]

Dan,

Good question. This is a "highly idealized" study to mainly illustrate the point that the "long-term" consequences of the two emission sources are very different. The key message we wanted to convey was that the FF emissions add external carbon to the climate system (atmosphere, land biosphere and ocean) while LULCC fluxes are just an internal arrangement of carbon in the climate system. A fraction of the externally added carbon would stay in the atmosphere for millennia while internally added carbon to the atmosphere could be completely removed in the absence of further human intervention. 

It is not always true that deforested area remains deforested. A good example is the abandoned agricultural areas in the mid-latitudes where there is regrowth of forests. I am sure we can endlessly argue about the fate of deforested land and the realism of the scenario employed in our study. The key scientific message should not be lost by giving too much importance to specific scenarios.

Cheers

Bala

[Tom Goreau]

Thanks for the reality check, Dan! Most deforested areas, even when planted to tree crops, never match the biomass they replace. And what we usually see is not secondary forest, invasive weeds take over after the land is abandoned because cattle starve and crops fail after the nutrients from forest burning are lost.

 

In 1984 we found that primary Amazonian rainforest with hundreds of tree species, when simply clearcut and abandoned, without even being farmed or grazed, were replaced almost entirely by just three worthless weed species: a tree with wood that is useless for firewood (Cecropia), a poisonous spiny relative of deadly nightshade that kills cows that eat it, and a magnificent red passion flower that unfortunately bore no fruit.

To view this discussion on the web visit https://groups.google.com/d/msgid/CarbonDioxideRemoval/C777AB41-612A-4EEC-B96A-E2F08DBA2CD0%40earthinnovation.org.