ICOS Science Conference 2022: Day 3, Session 21

1. Interpreting 2020 growth in
atmospheric carbon dioxide
concentrations as fossil fuel
emissions declined
Ben Poulter1, Lionel Arteaga Quintero1, Sourish Basu1, Abhishek Chatterjee2,
Joanna Joiner1, Alexei Lyapustin1, Lesley Ott1, Cecile Rousseaux1, Yujie Wang1,
Brad Weir1, Yasuko Yoshida1, and Zhen Zhang1

2. COVID-19 impact on economy led to 3-13%
decline in 2020 CO2 emissions (-2.6 GtCO2)
Decline in fossil fuel emissions of ~2.6 GtCO2
• -13% Google mobility data (Forster et al., 2020)
• -6.9% (-2.7 to -10.8%) (Le Quéré et al., 2020)
• -7% GCB-mean (Friedlingstein et al., 2020)
• -7% IEA World Energy Outlook (2020)
• -7% (Le Quéré et al., 2021)
• -6.5% Carbon Monitor (Liu et al., 2020)
• -6% monthly energy data (Le Quéré et al., 2021)
• -5.8% GCB (Friedlingstein et al., 2020)
• -5.8% IEA Global Energy Review (2021)

3. Greenhouse-gas satellites, OCO-2, detected
regional XCO2 anomalies in spring 2020
OCO-2 soundings
GEOS assimilation

4. Despite reduced emissions, 2020 atmospheric CO2
increased by 18.4 GtCO2 (+2.35 ppm)

5. • Research Questions:
1. How well does the MBL growth rate
integrate temporal lags and spatial
contributions?
2. Was the land carbon sink weaker in 2020
due to droughts and heatwaves and fires?
3. Was the ocean carbon uptake lower due to
La Niña-like conditions?
4. Can greenhouse-gas satellites provide low-
latency marine boundary layer GHG
information?
What happened to the imprint of COVID-19 on
atmospheric CO2 growth?

6. 1) Uncertainty in GHG networks ?
N
80°N
60°N
40°N
20°N
0
20°S
40°S
60°S
80°S
70°N
50°N
30°N
10°N
10°S
30°S
50°S
70°S
160°E
120°E
80°E
40°E
0
40°W
80°W
120°W
160°W
140°E
100°E
60°E
20°E
20°W
60°W
100°W
140°W
0°
180° 120°W 60°W 0° 60°E 120°E 180°
Longitude
Latitude
NOAA Marine Boundary Layer sites in the GGGRN – flask sites only (43)
(excluding ICOS, French, and WDCGG, if MBL sites only)
• COVID-19 led to reporting delays & other potential effects on sampling
• Does gradual loss of MBL sites make network more sensitive to meteorological variability & sampling error?
• Sensitivity analysis confirmed NOAA reported uncertainty range (0.08 ppm)
• However, NOAA growth rate algorithm requires 3-4 months of 2021 data
2000 2005 2010 2015 2020
spo
hba
syo
psa
crz
cgo
ams
pocs35
pocs30
pocs25
pocs20
pocs15
smo
abp
pocs10
asc
pocs05
poc000
chr
pocn05
pocn10
rpb
gmi
pocn15
avi
kum
pocn20
pocn25
key
mid
pocn30
bmw
bme
azr
shm
mhd
cba
ice
stm
brw
mbc
zep
alt
0.0
0.5
1.0
1.5
2.0
2.5
3.0
CO
2
growth
Rate
(ppm)
-150 -100 -50 0 50 100 150
-50
0
50
Longitude (°)
-150 -100 -50 0 50 100 150
-50
0
50
Longitude (°)
Latitude
(°)
0
50
0
50
titude
(°)
NOAA GGGRN MBL Sites MAM 2020 Wind Vectors
CO2 growth anomalies

7. NASA GEOS-5 CO2 tracer experiment
NOAA GGGRN sites (south to north)
spo
hba
syo
psa
crz
cgo
ams
pocs35
pocs30
pocs25
pocs20
pocs15
smo
abp
pocs10
asc
pocs05
poc000
chr
pocn05
pocn10
rpb
gmi
pocn15
avi
kum
pocn20
pocn25
key
mid
pocn30
bmw
bme
azr
shm
mhd
cba
ice
stm
brw
mbc
zep
alt
0
1
2
3
4
5
6
• Tagged fossil (EDGAR), land (LPJ, CN, ED), ocean (NOBM)
and fire (QGFED) tracers
• Sampled NOAA GGGRN MBL sites
Increased atmospheric CO2 growth at all stations
Reduced fossil fuel contribution
Delta
CO
2
ppm

8. NASA GEOS-5: Land contribution to CO2
growth
Delta
CO
2
ppm
LPJ
Catchment CN
ED
NOAA GGGRN sites (south to north)
Reduced southern hemisphere CO2 uptake (0-0.2 ppm)
Disagreement in northern hemisphere CO2 uptake (-0.2 to +0.2 ppm)

9. NASA GEOS-5: Fire contribution to CO2 growth
Delta
CO
2
ppm
NOAA GGGRN sites (south to north)
Increased fire CO2 contribution in southern hemisphere
Intense 2020 fire season in southern hemisphere
increased CO2 growth (0 to 0.04 ppm)
• Australia black summer
• Brazil deforestation fires
• Parana drought fires

10. NASA GEOS-5: Ocean contribution to CO2
growth
Delta
CO
2
ppm
NOAA GGGRN sites (south to north)
Agreement for increased ocean uptake between prognostic and data-driven ocean
models (-0.05 to -0.25 ppm)
NOBM
Landshutzer

11. Teleconnections in 2020 – ENSO, AO and IOD
• ENSO 3.4, Indian Ocean Dipole (IOD),
and Arctic Oscillation (AO) had varying
moderate to extreme states
• Positive to negative phase shift in ENSO,
moderate La Niña (early 2020 fires in
Australia, S America drought)
• Extreme positive phase IOD, wetter than
usual South Asia
• Extreme positive phase AO (Saji, Nature
1999) brought early heatwave to Siberia

12. Vegetation and hydrology anomalies
MODIS MAIAC NDVI anomalies (spring 2020)
SON
MAM
GRACE water storage anomalies
• Early green-up in Asia, and browning over Australia
• Abnormally dry summer / fall conditions in South America

13. Agreement in growth rate estimates between
ground networks and satellite-based methods
• Total XCO2 is benchmark similar to NOAA MBL
• Agreement in IAV
• No systematic bias
• Approaches within the NOAA MBL uncertainty
• Imbalance between GCP forecast
• Move retrievals of (e.g., OCO-2) XCO2 toward faster
reporting than flask networks
Toward lower-latency atmospheric CO2 growth
rates
2015 2016 2017 2018 2019 2020
1.5
2.0
2.5
3.0
Atmospheric
growth
rate
(ppm
CO
2
)
NOAA GML
NOAA GML (Basu)
NOAA GML (excl. KEY+MHD)
NOAA GML (GEOS)
Global MBL (GEOS)
XCO2 (GEOS)
GCP projection
GCP: 2016+2017
Betts approach
GCP: 2018-2020
Holt-Winter fit to
extend Sept-Dec

14. Explaining the discrepancy in 2020 atmospheric
CO2 growth and reduced emissions
• Sustained atmospheric CO2 growth, near El Nino-type levels, largely due to reduced
land carbon uptake
• Fires in 2020 also played a smaller role in increased atmospheric growth anomalies
(at annual, regional scales)
• Ocean carbon uptake appeared to increase, potentially with cooler southern ocean
conditions
• Agreement in growth rate estimates between ground networks (GGGRN) and
satellite retrievals (OCO-2) show promise for reducing latency of carbon budgets
• Contact: benjamin.poulter@nasa.gov