Consequences

[bpbond]

What if GPP is really 150 PgC/yr, not 125?

• Lisa Welp was right
• A number of CMIP5 models, mostly notably CESM, are much too low
• MODIS and MTE far too low
• Upscaling wrong? (E.g. not accounting for tropical forests correctly.) Or is FLUXNET underestimating GPP?
• More rapid cycling of C than thought
• Residence time lower, and turnover higher, than thought?
• Consistent? "...we find that the ecosystem carbon turnover times simulated by state-of-the-art coupled climate/carbon-cycle models vary widely and that numerical simulations, on average, tend to underestimate the global carbon turnover time by 36 per cent." Carvalhais et al. 2014

What is Rs is really 60 Pg C/yr, not 85?

• Our upscaling of chamber measurements is fundamentally wrong
• Some unexpected constraint? E.g. tropical data is not representative of full suite of productivity, biased high?
• ESMs such as Had-GEM2 are too high - either in their temperature sensitivity, or basal rates, or ...?
• The oldest global Rs estimates are much more accurate than ones in the last 20 years

[bpbond]

Also "The results suggest that previous eddy-covariance-based estimates of global photosynthesis and respiration are probably biased high" Keenan et al. 2019

[bpbond]

From Nature brief: "The data could mean that the world's landmasses are taking up 7% more C than scientists thought" re https://www.atmos-chem-phys.net/19/8687/2019/

[bpbond]

"Model uncertainty—as measured by intermodel spread—is high for soil carbon turnover time (τ) and exceeds the uncertainty estimated for carbon uptake through gross primary production (GPP) (15, 16)." https://science.sciencemag.org/content/353/6306/1419

[jinshijian]

2019-9-4 meeting summary (1) Cut GPP and RS estimates after 1985 or 1990. (2) Comparing with CMIP6 GPP. (3) Think about implications: a. ESMs may be calibrated against wrong benchmark numbers; b. terrestrial C turnover time may be wrong; c. how can this change our understanding of global carbon cycling?

2019-9-9 meeting summary (1) Give GPP more categories (2) Try to break GPP down to high, middle, and tropic

[bpbond]

Why might Rs be too high? Perhaps soil moisture effects we're not accounting for? E.g. cite Stocker et al. (2019).