The main findings for 2023, as published in National Science Review.
The global land carbon sink fell to its weakest level since 2003
This was the first low latency budget. In 2023 the CO2 growth rate hit a record high while fossil emissions barely grew, implying an unprecedented weakening of natural sinks. Bottom-up models and an OCO-2 inversion place the global net land sink at 0.44 ± 0.21 GtC yr−1, driven by the Amazon drought, extreme fires in Canada and extreme heat, mostly in the tropics.
- The CO2 growth rate reached a record 3.37 ± 0.11 ppm yr−1 at Mauna Loa (2.82 ± 0.08 ppm yr−1 for the marine boundary layer), 86% above 2022, while fossil CO2 emissions increased by only 0.1–1.1%.
- The global net land sink fell to 0.44 ± 0.21 GtC yr−1, the weakest since 2003.
- The largest abnormal carbon loss was in the Amazon during the drought of the second half of 2023 (0.31 ± 0.19 GtC yr−1), with a further loss in Southeast Asia (0.13 ± 0.12 GtC yr−1); extreme fires in Canada emitted 0.58 ± 0.10 GtC yr−1.
- Since 2015 the land sink north of 20°N has declined by half, to 1.13 ± 0.24 GtC yr−1 in 2023, while the tropics switched to a carbon loss (0.56 ± 0.23 GtC yr−1) with the developing El Niño.
- Land regions exposed to extreme heat contributed a gross carbon loss of 1.73 GtC yr−1.
The budget at a glance
| Quantity | January–December 2023 | Notes |
|---|---|---|
| Atmospheric CO2 growth rate | 2.82 ± 0.08 ppm yr−1 | NOAA marine boundary layer; 3.37 ± 0.11 at Mauna Loa (record high) |
| Fossil CO2 emissions | 10.20 ± 0.05 GtC yr−1 | +0.1% to +1.1% compared with 2022 |
| Net land sink | 0.44 ± 0.21 GtC yr−1 | Mean of DGVMs (0.14 ± 0.28) and OCO-2 inversion (0.73 ± 0.30) |
| Ocean sink (emulators) | 2.60 ± 0.72 GtC yr−1 | Ocean model emulators; OCO-2 inversion 2.33 ± 0.20 |
| Budget imbalance | 1.26 GtC yr−1 | Against the marine boundary layer growth rate; 0.09 against Mauna Loa |
Values as published. Uncertainties are ±1σ across ensemble members unless stated.
Models and data used
- Fossil CO2 emissions. Carbon Monitor and the Global Carbon Budget method (average of the two)
- Atmospheric growth rate. NOAA marine boundary layer (MBL) and Mauna Loa (MLO)
- Land, bottom-up. 3 DGVMs driven by ERA5: ORCHIDEE, JULES, OCN; fire emissions from GFED4.1s and GFAS
- Ocean, bottom-up. Machine-learning emulators of 5 ocean biogeochemical models and 8 data products (GCB 2022)
- Top-down. 1 OCO-2 atmospheric inversion: CAMS
- Anomaly reference. 2015–2022
Publication
Ke, P., Ciais, P., Sitch, S., Li, W., Bastos, A., Liu, Z., et al. (2024). Low latency carbon budget analysis reveals a large decline of the land carbon sink in 2023. National Science Review, 11(12), nwae367. https://doi.org/10.1093/nsr/nwae367