Top–down assessment of the Asian carbon budget since the mid 1990s

Increasing atmospheric carbon dioxide (CO2) is the principal driver of anthropogenic climate change. Asia is an important region for the global carbon budget, with 4 of the world's 10 largest national emitters of CO2. Using an ensemble of seven atmospheric inverse systems, we estimated land biosphere fluxes (natural, land-use change and fires) based on atmospheric observations of CO2 concentration. The Asian land biosphere was a net sink of −0.46 (−0.70–0.24) PgC per year (median and range) for 1996–2012 and was mostly located in East Asia, while in South and Southeast Asia the land biosphere was close to carbon neutral. In East Asia, the annual CO2 sink increased between 1996–2001 and 2008–2012 by 0.56 (0.30–0.81) PgC, accounting for ∼35% of the increase in the global land biosphere sink. Uncertainty in the fossil fuel emissions contributes significantly (32%) to the uncertainty in land biosphere sink change.

Since the global total in each inversion is scaled to be consistent with the CDIAC global total (except WU which used EDGAR) this difference is not significantly different from zero and, therefore, is not shown.       This study includes seven independent inversion systems each with a different transport model, prior land biosphere and ocean fluxes, as well as fossil fuel and cement (FFC) emission estimates (see Supplementary Table 1). In all inversions, the prior FFC emissions estimate was scaled so that the annual global total was approximately consistent with the CDIAC inventory (http://cdiac.ornl.gov/trends/emis/meth_reg.html), except WU, which used the EDGAR version 4.2 inventory. However, the spatial distribution and temporal variability among inversions differed (Supplementary Table 1). Both JMA and CSIRO used a fixed spatial distribution (time invariant) for the fluxes. While CSIRO scaled the regional total emissions to match CDIAC, JMA scaled the global total emission, which led to much lower rates of FFC emission increase for East Asia after 2000 (since the East Asian emissions increased faster than the global mean). NIES and CAO used the ODIAC inventory 8 , while the remaining inversions based the spatial distribution on EDGAR version 4.2 (http://edgar.jrc.ec.europa.eu). (The prior FFC emissions for each inversion system are shown in Supplementary Fig. 1 and 2).

Supplementary Note 2
In the post processing and analysis, we used FFC emission estimates from three different inventories, CDIAC (http://cdiac.ornl.gov/trends/emis/meth_reg.html), IEA (https://www.iea.org) and EDGAR version 4.2 (http://edgar.jrc.ec.europa.eu). The posterior land biosphere fluxes were calculated by subtracting each of these FFC estimates from the total posterior fluxes. In each inventory, the bunker fuels, i.e., fuel used in international aviation and maritime transport, were included in the global total but not in the regional totals. The IEA inventory does not include estimates for emissions from cement production, therefore, the estimates for this source from CDIAC were added to the IEA estimates.

Supplementary Note 3
The NOAA ESRL GMD Observation Package 9 brings together direct (ground-based) measurements of CO 2 from multiple laboratories in a standard format along with detailed meta-data. Details about the Observation Package and a link to download the data is available here: http://www.esrl.noaa.gov/gmd/ccgg/obspack/. The GlobalView-CO 2 package 10 is a data product based on a selection of concentration data for baseline conditions at each observation site. Details about GlobalView-CO 2 and a link to download the data is available here: http://www.esrl.noaa.gov/gmd/ccgg/globalview/co2/co2_intro.html.
For validation, we have used the CONTRAIL (Comprehensive Observation Network for TRace gases by AIrLiner) data 11 . The CONTRAIL measurements are made from commercial aircraft flying on a regular basis between Japan East, South and Southeast Asia, as well as to Australia, Hawaii and North America. We have used measurements made using an in-situ analyzer, i.e., the CONTRAIL Continuous CO 2 Measuring Equipment (CME). The CME consists of a LICOR LI-840 non-dispersive infrared analyzer, data logger and gas handling instrumentation (for details see reference 4). Air is sampled from an inlet mounted at the aircraft's air conditioning intake duct. Details about CONTRAIL and how to access the data can be found here: http://www.cger.nies.go.jp/contrail/index.html.

Supplementary Note 4
Vegetation activity data were analysed with Advanced Very High Radiometric Resolution (AVHRR) observations of the Normalized Difference Vegetation Index (NDVI). NDVI