You all may have seen the news report “Grasslands More Reliable Carbon Sink Than Trees” I’m not exactly sure whether this site is a source of UC Davis press releases, or a more broad climate communications site.
Their basic argument is that because forests have most of their carbon above ground, and they burn up that carbon in wildfires (the video has a very nice graphic that depicts this), then grasslands are better because their carbon doesn’t burn up. First, note that this statement claims that this scientific information is relevant to policy in terms of California’s cap and trade program.
A study from the University of California, Davis, found that grasslands and rangelands are more resilient carbon sinks than forests in 21st century California. As such, the study indicates they should be given opportunities in the state’s cap-and-and trade market, which is designed to reduce California’s greenhouse gas emissions to 40 percent below 1990 levels by 2030.
So we are talking investments conceivably in the next 10 years to reduce GHGs. But what was most peculiar to me was how they went about figuring this out, and some of their results. First of all, they referred to RCP 8.5 as a “business as usual” scenario. If this were a NEPA document, we might say that there is scientific controversy around that claim. Many would say that it’s a “useful worst case scenario” not “business as usual”. Of course, you don’t have to have a Ph.D. in atmospheric physics to think that people might disagree about what’s likely to happen in the future, and that prophecy is unlikely to have a meaningful probability distribution.
Most interesting to me, though, were their efforts to predict where trees would go away and be replaced by grasslands under that climate scenario. This can be seen in the figure above, and also a figure I couldn’t copy that is a placeholder for the video for the paper here.
Tree or grass people might wonder, how could you possibly predict that, given what we know of trees and grasses? Well, it’s possible to link a variety of models. I think the authors did real nice work in explaining their paper, using an open source journal and describing the limitations of their work.
Here’s the first sentence of their results and conclusions:
In contrast to the conventional paradigm, we show that the inherent resilience of grassland vegetation to drought and wildfire (figure 1) translates to a more reliable C sink than forest ecosystems (figure 2) in response to 21st century climate changes.
But their caveats include:
Factors such as species traits, biodiversity, rapid evolution, and human management intervention could alter our model-based findings from the projections provided here. Consequently, our results indicate the potential direction of change as opposed to predictions that consider the full ensemble of ecological, physiological and management factors that can alter pathways and responses of ecosystems to climate change.
(my bold, human management intervention like fire suppression?) In what sense is it realistic to model the carbon impacts of future wildfires while not considering fire suppression?
Future work could focus on such factors as the evolutionary history of trees to fire, the physiological adaptations of ecosystems as well as regional species to fire, drought and climate change, the effects of biodiversity on ecosystem resilience as well as a comprehensive analysis of the goods and services provided by forests and grasslands.
The research was funded by the National Science Foundation. I wonder if on their research panels, there is ever a thought of “is there a point at which running models has little real world data that the information produced is not worth funding, or we should be clear that it is basic science with no real-world relevance? NSF doesn’t have to care whether its research is policy relevant, because its mission in broader than that, it’s mission is to “advance the progress of science” but as I’ve argued before, if researchers make the claim that it is, perhaps there should be some kind of standard. For those of you who haven’t seen my effort in this direction here’s a link to Eight Steps to Vet Scientific Information for Policy Fitness.
On wonders whether if the California policy makers had (1) framed the questions they felt they needed answered relevant to their cap n trade program (2) reviewed existing literature on grasslands, forests, trees, drought, fires and climate change, would they have prioritized this kind of study?