Carbon fluxes from land 2000–2020: bringing clarity to countries' reporting
Authors: Grassi Giacomo , Conchedda Giulia , Federici Sandro , Abad Viñas Raul , Korosuo Anu , Melo Joana , Rossi Simone , Sandker Marieke , Somogyi Zoltan , Vizzarri Matteo , Tubiello Francesco N. 
Published: October 2022

Abstract. Despite an increasing attention on the role of land in meeting countries'
climate pledges under the Paris Agreement, the range of estimates of carbon
fluxes from land use, land-use change, and forestry (LULUCF) in available
databases is very large. A good understanding of the LULUCF data reported by
countries under the United Nations Framework Convention on Climate Change
(UNFCCC) – and of the differences with other datasets based on country-reported data – is crucial to increase confidence in land-based climate
change mitigation efforts. Here we present a new data compilation of LULUCF fluxes of carbon dioxide
(CO2) on managed land, aiming at providing a consolidated view on the
subject. Our database builds on a detailed analysis of data from national
greenhouse gas inventories (NGHGIs) communicated via a range of country
reports to the UNFCCC, which report anthropogenic emissions and removals
based on the IPCC (Intergovernmental Panel on Climate Change) methodology.
Specifically, for Annex I countries, data are sourced from annual GHG
inventories. For non-Annex I countries, we compiled the most recent and
complete information from different sources, including national
communications, biennial update reports, submissions to the REDD+
(reducing emissions from deforestation and forest degradation) framework, and
nationally determined contributions. The data are disaggregated into fluxes
from forest land, deforestation, organic soils, and other sources (including
non-forest land uses). The CO2 flux database is complemented by
information on managed and unmanaged forest area as available in NGHGIs. To
ensure completeness of time series, we filled the gaps without altering the
levels and trends of the country reported data. Expert judgement was applied
in a few cases when data inconsistencies existed. Results indicate a mean net global sink of −1.6 Gt CO2 yr−1 over the
period 2000–2020, largely determined by a sink on forest land (−6.4 Gt CO2 yr−1), followed by source from deforestation (+4.4 Gt CO2 yr−1),
with smaller fluxes from organic soils (+0.9 Gt CO2 yr−1) and other
land uses (−0.6 Gt CO2 yr−1). Furthermore, we compare our NGHGI database with two other sets of
country-based data: those included in the UNFCCC GHG data interface, and
those based on forest resources data reported by countries to the Food and Agriculture Organization of the United Nations (FAO) and used
as inputs into estimates of GHG emissions in FAOSTAT. The first dataset,
once gap filled as in our study, results in a net global LULUCF sink of −5.4 Gt CO2 yr−1. The difference with the NGHGI database is in this case
mostly explained by more updated and comprehensive data in our compilation
for non-Annex I countries. The FAOSTAT GHG dataset instead estimates a net
global LULUCF source of +1.1 Gt CO2 yr−1. In this case, most of the
difference to our results is due to a much greater forest sink for non-Annex
I countries in the NGHGI database than in FAOSTAT. The difference between
these datasets can be mostly explained by a more complete coverage in the
NGHGI database, including for non-biomass carbon pools and non-forest land
uses, and by different underlying data on forest land. The latter reflects
the different scopes of the country reporting to FAO, which focuses on area
and biomass, and to UNFCCC, which explicitly focuses on carbon fluxes.
Bearing in mind the respective strengths and weaknesses, both our NGHGI
database and FAO offer a fundamental, yet incomplete, source of information
on carbon-related variables for the scientific and policy communities,
including under the Global stocktake. Overall, while the quality and quantity of the LULUCF data submitted by
countries to the UNFCCC significantly improved in recent years, important
gaps still remain. Most developing countries still do not explicitly
separate managed vs. unmanaged forest land, a few report implausibly high
forest sinks, and several report incomplete estimates. With these limits in
mind, the NGHGI database presented here represents the most up-to-date and
complete compilation of LULUCF data based on country submissions to UNFCCC. Data from this study are openly available via the Zenodo portal (Grassi et
al., 2022), at https://doi.org/10.5281/zenodo.7190601.