We will need extensive CH4 capture, as well as CO2 capture, technologies.
It seems to me that the linked reference (and associated article) about biospheric feedback effect in a synchronously coupled model of human and Earth system is a play to try to document the potential validity of negative emissions technology like BECCS using ACME (Phase 1). While ACME tries to account for the impact of phosphorous on the biosphere, I am concerned that much of their focus on BECCS is just happy talk, which will not prevent a socio-economic collapse in the 2050 to 2060 timeframe. Nevertheless, it appears that these BECCS assumptions & associated projections will be rolled into both CMIP6 and AR6 to further the illusion that the situation is in capable hands (i.e. the DOE [which runs ACME] controlled by Rick Perry).
My point is that no matter how serious our situation is, decision makers like Rick Perry can always use happy talk about all the future CO2 and/or CH4 negative emissions technology that we are going to deploy in a few decades, just so that they don't have to do anything significant to lower emissions right now:
Peter E. Thornton et al, Biospheric feedback effects in a synchronously coupled model of human and Earth systems, Nature Climate Change (2017). DOI: 10.1038/nclimate3310
http://www.nature.com/nclimate/journal/v7/n7/full/nclimate3310.html?foxtrotcallback=trueAbstract: "Fossil fuel combustion and land-use change are the two largest contributors to industrial-era increases in atmospheric CO 2 concentration. Projections of these are thus fundamental inputs for coupled Earth system models (ESMs) used to estimate the physical and biological consequences of future climate system forcing. While historical data sets are available to inform past and current climate analyses, assessments of future climate change have relied on projections of energy and land use from energy–economic models, constrained by assumptions about future policy, land-use patterns and socio-economic development trajectories. Here we show that the climatic impacts on land ecosystems drive significant feedbacks in energy, agriculture, land use and carbon cycle projections for the twenty-first century. We find that exposure of human-appropriated land ecosystem productivity to biospheric change results in reductions of land area used for crops; increases in managed forest area and carbon stocks; decreases in global crop prices; and reduction in fossil fuel emissions for a low–mid-range forcing scenario. The feedbacks between climate-induced biospheric change and human system forcings to the climate system—demonstrated here—are handled inconsistently, or excluded altogether, in the one-way asynchronous coupling of energy–economic models to ESMs used to date."
See also the associated linked article entitled: Titan simulations show importance of close two-way coupling between human and Earth systems"
https://phys.org/news/2017-07-titan-simulations-importance-two-way-coupling.htmlExtract: "Through the Advanced Scientific Computing Research Leadership Computing Challenge program, Thornton's team was awarded 85 million compute hours to improve the Accelerated Climate Modeling for Energy (ACME) effort, a project sponsored by the Earth System Modeling program within DOE's Office of Biological and Environmental Research. Currently, ACME collaborators are focused on developing an advanced climate model capable of simulating 80 years of historic and future climate variability and change in 3 weeks or less of computing effort.
Now in its third year, the project has achieved several milestones—notably the development of ACME version 1 and the successful inclusion of human factors in one of its component models, the iESM.
"What's unique about ACME is that it's pushing the system to a higher resolution than has been attempted before," Thornton said. "It's also pushing toward a more comprehensive simulation capability by including human dimensions and other advances, yielding the most detailed Earth system models to date.
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The development of iESM started before the ACME initiative when a multilaboratory team aimed to add new human dimensions—such as how people affect the planet to produce and consume energy—to Earth system models. The model—now a part of the ACME human dimensions component—is being merged with ACME in preparation for ACME version 2.
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ACME version 1 will be publicly released in late-2017 for analysis and use by other researchers. Results from the model will also contribute to the Coupled Model Intercomparison Project, which provides foundational material for climate change assessment reports."