Bookkeeping estimates of the net land-use change flux a sensitivity study with the CMIP6 land-use dataset

Neglecting wood harvest (NoH) or only using net transitions (net) leads to 3 times larger deviations from the reference (see Table 2) than LULCC uncertainties (first column) and reduces the net LULCC flux at most to about 1.1 PgC yr−1. The 5 %–10 % sensitivity of the net LULCC flux to LULCC uncertainties (about 1.55 to 1.75 PgC yr−1) can mainly be explained by the uncertainty of transitions. Almost no sensitivity of the net LULCC flux to the starting year of the model simulations remains. The impact of StYr and LULCC uncertainty on the net LULCC flux in 2014 is similar to the characteristics discussed for the cumulative net LULCC flux estimates (Fig. 3). LULCC differences still modulate annual net LULCC flux estimates throughout the 20th century (Fig. S2), and the largest variability of net LULCC flux, about ±0.1 to 0.3 PgC yr−1, is due to uncertainties in harvest and abandonment.

Our findings and discussions regarding DGVM studies are therefore also informative for the interpretation of CMIP6 results. BLUE is a data-driven bookkeeping model (Hansis et al., 2015) used in the GCB for LULCC flux estimates (Friedlingstein et al., 2019). We choose a bookkeeping model in contrast to a DGVM because LULCC fluxes due to individual LULCC events can be traced and because of the potential to isolate the net LULCC flux independent of climate variability, among other factors (Pongratz et al., 2014). The cumulative net LULCC flux exhibits a reduced sensitivity to LULCC uncertainty with starting year 1850 (compare vertical spread of blue markers in the LULCC column) since the input data have smaller uncertainty in more recent years (Fig. A1). At the same time, the largest estimates of the cumulative net LULCC flux comparing experiments with different StYr are produced in simulations from 1850 (second column).

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The baseline SSP4 scenario (SSP4-6.0) represents an evolution of progress with high agricultural productivity and environmental policies (reduced deforestation, re- and afforestation, etc.) in high-income countries and the opposite in low-income countries. The alternative scenario (SSP4-3.4) is based on more stringent mitigation policies, e.g. a larger carbon price. Similar to SSP5, the increase in cropland area is larger in the lower RCP scenario, namely 14 % and 80 % respectively for RCP6.0 and RCP3.4 between 2010 and 2100.

• A brief description of how the LUH2 dataset is prepared for use with the BLUE model and short discussion of the properties of the LULCC dataset are provided in the Appendix (Sects. A1 and A2).
• As a first step, we present the bookkeeping model BLUE used in this study.Then the LUH2 dataset, its high and low LULCC scenarios as well as various future scenarios are introduced.
• These results, albeit from a single model, are important for CMIP6 as they compare the relative importance of starting year, uncertainty of LULCC, applying gross transitions and wood harvest on the net LULCC flux.
• The relative change due to neglecting gross transitions is similar across LULCC setups, and for REG1700net the cumulative net LULCC flux is reduced to 211 PgC.
• The LUH2 dataset (Hurtt et al., 2020) provides historical land-use estimates from 850 with uncertainty estimates for agricultural land area (from the History Database of the Global Environment, HYDE; Klein Goldewijk et al., 2017) and wood harvest (Zon and Sparhawk, 1923; Kaplan et al., 2017).
• Furthermore, all setups roughly exhibit the same ratio of net LULCC flux with net or gross transitions.

The baseline SSP5 scenario (SSP5-8.5) on the other hand starts off with a minor maximum of the net LULCC flux which is followed by a declining estimate. The initial peak in SSP5 is mainly caused by pasture expansion and wood harvest (Fig. A3); the evolution of secondary land bookkeeping model and cropland is similar to that in the SSP4 baseline, but less area is used for pasture. In the alternative 3.4OS scenario, which differs from the SSP5 baseline mainly after 2040, a secondary peak after around 2050 is present, mainly caused by crop expansion over pasture.

B1 Discussion of crossing points of net LULCC flux simulations

At the end of the historical LULCC dataset in 2014, the LULCC uncertainty retains some impact on the net LULCC flux (±0.15 PgC yr−1 at an estimate of 1.7 PgC yr−1). Of the past uncertainties in LULCC, a small impact persists in 2099, mainly due to uncertainty of harvest remaining in 2014.However, compared to the uncertainty range of the LULCC flux estimated today, the estimates in 2099 appear to be indistinguishable. Since harvest is provided in the LUH2 dataset based on the cover type (forest or non-forest), transitions are not used in BLUE when the cover type does not match.

However, harvest on forested primary land, which is most important for the net LULCC flux, is similar between REG and LO (Fig. A2) and thus causes the similarity in net LULCC flux. Harvest on secondary land does not produce a net flux to the atmosphere if considered over a long time-period (total source is equivalent to total sink). From about 1800 onwards, less harvest on primary land can be observed in the HI LULCC estimate, slightly more in LO and the most in REG.

Assessing and modeling the impact of land use and changes in land cover related to carbon storage in a western basin in Mexico

A part of the BLUE model simulations was executed on the Linux cluster hosted by the Leibniz-Rechenzentrum in Munich. Figure A5Differences in primary land area in BLUE and LUH2 in 2014 for REG850 (a), REG1700 (d) and REG1850 (g). Differences HI-REG  (b, e, h) and LO-REG (c, f, i) of BLUE-LUH2 primary land area for the same years as in panels (a, d, g). All rights are reserved, including those for text and data mining, AI training, and similar technologies.

• Since the other LULCC activities influence the available biomass, more or less area might be required in order to fulfil the harvested biomass demand.
• Start with a free account to explore 20+ always-free courses and hundreds of finance templates and cheat sheets.
• Bookkeeping involves the recording, on a regular basis, of a company’s financial transactions.
• In DGVM simulations, a higher CO2 exposure will most likely lead to larger vegetation and soil carbon stocks in the 20th century in low simulations as compared to high land-use simulations.
• Many small companies don’t actually hire full-time accountants to work for them because of the cost.
• Although total harvest biomass is designed to be equal across scenarios after (Hurtt et al., 2020), this is not true for harvested area, since harvested area is derived such that the demanded harvested biomass can be fulfilled.

However, there are large coherent areas over Central and North America and northern Europe/Asia with reduced cumulative net LULCC flux in LO1700 compared to REG1700. The time series of all three historical uncertainty estimates (Fig. 1) shows the known feature of a peak in 1960 (Hansis et al., 2015; Friedlingstein et al., 2019). Before around 1960, the net LULCC flux is almost continuously rising and levels decrease after 1960 to the end of the historical LULCC dataset in 2014. Around 2000, the annual net LULCC flux is of similar magnitude to that in the early 20th century. Table 3Overview of future sensitivity experiments, continued from simulations with starting year 1700 for all three LULCC scenarios (see Table 2).

A2 Properties of the LULCC dataset

For simulations that started in 1700 and 1850, the difference in primary land extent in 2014 is at most 4 % (Fig. A5), which is also true for REG and LO in 850. In all cases, the amount of primary land is larger in BLUE than in the original LUH2 dataset, at the cost of other land-cover types. Overall, this means that the total amount of net LULCC flux will be underestimated in BLUE, the most in the HI850 experiment. These results, albeit from a single model, are important for CMIP6 as they compare the relative importance of starting year, uncertainty of LULCC, applying gross transitions and wood harvest on the net LULCC flux. For the cumulative net LULCC flux over the industrial period, the uncertainty of LULCC is as relevant as applying wood harvest and gross transitions. However, LULCC uncertainty matters less (by about a factor of 3) than the other two factors for the net LULCC flux in 2014, and historical LULCC uncertainty is negligible for estimates of future scenarios.