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PUBLISHED ONLINE: 17 NOVEMBER 2009|DOI: 10.1038/NGEO689
A
tmospheric measurements of CO
2
concentration are highly
precise and provide an accurate, reliable measure of the
increase of CO
2
in the atmosphere every year
1
. Yet these meas-
urements cannot at present be used to verify global CO
2
emissions
estimated from energy data, because the uptake of CO
2
by the land
and ocean CO
2
sinks are not quantied with high enough accuracy.
Understanding the dierence in amount between anthropogenic
CO
2
emissions and changes in atmospheric CO
2
concentration
requires good estimates of the sinks and good attribution of the
causes of changes, both for the emissions and for their partitioning
between the natural reservoirs.
Global CO
2
emissions and their partitioning between the atmos-
phere and the land and ocean CO
2
sinks can be established using a
wide range of geophysical and economic data. We have constructed
a global CO
2
budget for each year during 1959–2008 and analysed
the underlying drivers of each component. e global increase in
atmospheric CO
2
was determined directly from measurements. CO
2
emissions from fossil fuel combustion were estimated on the basis
of countries’ energy statistics. CO
2
emissions from land-use change
(LUC) were estimated using deforestation and other land-use data,
re observations from space, and assumptions on the carbon density
of vegetation and soils and the fate of carbon. e time evolution of
the land and ocean CO
2
sinks, however, cannot be estimated directly
from observations. For these terms, we used state-of-the-art models
on which we imposed the observed meteorological conditions of the
past few decades. e resulting global CO
2
budget provides insight
into the global carbon cycle and the emerging trends.
Fossil fuel CO
2
emissions
CO
2
emissions from fossil fuel combustion, including small
contributions from cement production and gas aring, were
8.7±0.5 Pg C yr
−1
in 2008, an increase of 2.0% on 2007, 29% on
2000 and 41% above emissions in 1990 (Supplementary Table 1;
see Methods). Emissions increased at a rate of 3.4% yr
−1
between
2000 and 2008, compared with 1.0% yr
−1
in the 1990s (Fig. 1).
Emissions continued to track the average of the most carbon-
intensive family of scenarios put forward by the Intergovernmental
Panel on Climate Change
2,3
(IPCC; scenario A1FI in Fig. 1a). Since
1990, the growth in fossil fuel CO
2
emissions has been dominated
by countries that do not have emissions limitations in the so-called
non-Annex B of the Kyoto Protocol (mostly emerging economies
in developing countries), where emissions have more than doubled
in that time (Fig. 1b). Among Annex B countries (mostly advanced
Trends in the sources and sinks of carbon dioxide
Corinne Le Quéré, Michael R. Raupach, Josep G. Canadell, Gregg Marland
et al.*
Eorts to control climate change require the stabilization of atmospheric CO
2
concentrations. This can only be achieved
through a drastic reduction of global CO
2
emissions. Yet fossil fuel emissions increased by 29% between 2000 and 2008,
in conjunction with increased contributions from emerging economies, from the production and international trade of
goods and services, and from the use of coal as a fuel source. In contrast, emissions from land-use changes were nearly
constant. Between 1959 and 2008, 43% of each year’s CO
2
emissions remained in the atmosphere on average; the rest was
absorbed by carbon sinks on land and in the oceans. In the past 50 years, the fraction of CO
2
emissions that remains in the
atmosphere each year has likely increased, from about 40% to 45%, and models suggest that this trend was caused by a
decrease in the uptake of CO
2
by the carbon sinks in response to climate change and variability. Changes in the CO
2
sinks
are highly uncertain, but they could have a significant influence on future atmospheric CO
2
levels. It is therefore crucial to
reduce the uncertainties.
economies with emissions limitations), growth in some has been
oset by declines in others. is recent growth in CO
2
emissions
parallels a shi in the largest fuel emission source from oil to coal.
Coal contributed 40% of the fossil fuel CO
2
emissions in 2008,
compared with 37% for 1990–2000, whereas the contribution of
oil changed from 41% for 1990–2000 to 36% in 2008 (Fig. 1c). is
shi in the dominant source of fossil fuel emissions has reversed
the prevalence of oil since 1968. e growth in emissions since
2000 was also accompanied by an increase in the world per-capita
emissions from 1.1 metric tons of carbon in 2000 (Fig. 1d) to an
all-time high of 1.3 metric tons of carbon in 2008.
ere is growing evidence that the rapid growth in international
trade
4–10
and a shi of Annex B economic activity towards services
8
were signicant in driving non-Annex B CO
2
emission increases
due to fossil fuels. Several recent studies provide indicators of
the magnitude and time evolution of the share of non-Annex B
emission growth that was due to production of manufactured
products exported and consumed in Annex B countries. In 2001,
the equivalent of 0.22 Pg C was emitted in non-Annex B countries
to produce internationally traded products consumed in Annex B
countries
4
. In China alone, 30% of the growth in emissions between
1990 and 2002 was attributable to the production of exports from
China that were consumed in other countries
6
, and the share of the
growth increased to 50% between 2002 and 2005 (ref. 7). In 1990,
16% of Chinese emissions were from the production of exports,
increasing to 30% in 2005. Over half of the exported products were
destined for Annex B countries
6,7
. Complementary studies in some
Annex B countries showed that consumption-based emissions (that
is, emissions including imported products from non-Annex B coun-
tries, but excluding goods and services) were increasing faster than
emissions from domestic production
8,9
. In the UK, for instance,
within-country emissions decreased by 5% between 1992 and 2004,
whereas consumption-based emissions increased by 12% (ref. 8). In
the USA, within-country emissions increased by 6% between 1997
and 2004, whereas consumption-based emissions increased by 17%
(ref. 9). In both cases, a key factor driving the growth in consump-
tion-based emissions was the import of manufactured products
from China
6–9
. Taken together, these studies imply that a consider-
able share of the growth of emissions from non-Annex B countries
was associated with international trade. is explained around
one-quarter of the growth in non-Annex B emissions since 2000.
e growth in the world gross domestic product (GDP) was a
key driver in the recent increase in CO
2
emissions
2
. Consequently,
* A full list of authors and their aliations appears at the end of the paper.
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the global nancial crisis that aected markets in 2008 also had an
eect on the global CO
2
emissions and probably explains the mod-
est growth in emissions of 2.0% since 2007, compared with the faster
than average growth of 3.6% yr
−1
observed for 2000–2007. We predict
a decrease of 2.8% in global CO
2
emissions for 2009 using the change
in GDP projected by the International Monetary Fund (−1.1% as of
October 2009) and assuming that the carbon intensity of world GDP
has continued to improve following its long-term trend of −1.7% yr
−1
(refs 11, 12; Fig. 1a). e abrupt decrease in GDP in 2009 could bring
global CO
2
emissions back to just below their 2007 level and into the
middle range of the emissions scenarios that were used by the IPCC
to project climate this century
3
. e evolution of global CO
2
emis-
sions aer 2009 will depend on the subsequent trends in GDP and on
the evolution of the carbon intensity of GDP, for instance as a result of
countries following international agreements to curb CO
2
emissions.
Land-use change CO
2
emissions
Emissions from LUC are the second-largest anthropogenic source
of CO
2
. Deforestation, logging and intensive cultivation of crop-
land soils emit CO
2
. ese emissions are partly compensated by
CO
2
uptake from the regrowth of secondary vegetation and the
rebuilding of soil carbon pools following aorestation, aban-
donment of agriculture (including the fallow phase of shiing
cultivation), re exclusion and the shi to agricultural practices
that conserve soil carbon. Unlike fossil fuel emissions, which
reect instantaneous economic activity, LUC emissions are due to
both current deforestation and the carry-over eects of CO
2
losses
from areas deforested in previous years.
Here we have used a revised estimate
11
of the net CO
2
ux
resulting from LUC based on United Nations data for LUC areas
(available until 2005) and a book-keeping method
13
. For the period
1990–2005, net LUC CO
2
emissions were 1.5±0.7 Pg C yr
−1
, and were
dominated by tropical deforestation. In the deforestation process,
re is the primary means by which forests are converted to pastures
or croplands
14
, aer timber exploitation. To estimate LUC emissions
aer 2005, we used emissions due to re in deforestation areas
15
as a
proxy for deforestation emissions (Methods).
In 2008, the re emissions associated with deforestation were
0.3 Pg C yr
−1
less than their 1997–2008 average of 0.7 Pg C yr
−1
,
with the largest reductions being in southeast Asia (−65%) and
tropical America (−40%). Lower-than-average deforestation rates
reported in the Brazilian Amazon rainforest
16
corroborate lower
LUC emissions in 2008 in tropical America. Combining the
long-term average global LUC ux, 1.5 Pg C yr
−1
, with the 2008
deforestation re anomaly, −0.3 Pg C yr
−1
, our best estimate for
2008 LUC emissions is 1.2 Pg C yr
−1
. Wet La Niña conditions in
2008 probably limited re use and deforestation rates in southeast
Asia, particularly in Indonesia
17
. In the Amazon basin, climate
conditions were not anomalous, suggesting that other factors
caused the decrease in 2008 deforestation rates, which for the
Brazilian Amazon rainforest was the continuation of a decreasing
trend following high deforestation rates in 2002–2004 (ref. 16).
Taken together, the total CO
2
emission from fossil fuel
combustion and LUC was 9.9±0.9 Pg C yr
−1
in 2008. e rela-
tive contribution of LUC CO
2
emissions to total anthropogenic
CO
2
emissions decreased from 20% in 1990–2000 to 12% in
2008, owing to increasing fossil fuel emissions and below-aver-
age deforestation emissions in 2008. Although LUC emissions
were the smaller factor, their uncertainty, ±0.7 Pg C yr
−1
, is larger
than the uncertainty of ±0.5 Pg C yr
−1
associated with fossil fuel
emissions (Methods).
Atmospheric CO
2
growth and CO
2
sinks
On average, 43% of the total CO
2
emissions each year between
1959 and 2008 remained in the atmosphere, but this fraction is
Year
5
4
3
2
1
1990 1995 2000 2005 2010
Year
1990 1995 2000 2005 2010
Fossil fuel CO
2
emissions
(Pg C yr
–1
)
b
a
Year
4
3
2
1
0
1990 1995 2000 2005 2010
Fossil fuel CO
2
emissions
(Pg C yr
–1
)
c
Year
1.3
1.2
1.1
1990 1995 2000 2005 2010
Per-capita emissions
(metric tons of carbon per year)
d
Annex B
Non-Annex B
Oil
Coal
Gas
Cement
10
9
8
7
6
A1FI
A1B
A1T and B2
A2
B1
Fossil fuel CO
2
emissions
(Pg C yr
–1
)
Figure 1 | Fossil fuel CO
2
and per-capita emissions since 1990.
a–c, Fossil fuel emissions for the globe (a), Annex B countries (mostly
advanced economies; green) and non-Annex B countries (mostly
developing countries; blue) (b) and, specifically, coal (blue), oil (black),
gas combustion (green) and cement production (purple) (c). The data in
all panels are the annual mean data. Panel a also shows the projections
averaged by scenario family from the IPCC Special Report on Emissions
Scenarios (full coloured lines
3
), as in ref. 2. The grey shading in a is the
uncertainty in emissions. The blue shading covers all CO
2
emissions
scenarios used to project climate by the IPCC Fourth Assessment Report.
The red dot and dashed line in a are the projected CO
2
emissions for 2009
(see text). d, Global per-capita emissions.
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NATURE GEOSCIENCE DOI: 10.1038/NGEO689
subject to very large year-to-year variability (Fig. 2a). is ‘air-
borne fraction’ increased on average by 0.3±0.2% yr
−1
between
1959 and 2008. ere is a 90% probability that this increasing
trend is signicant taking into account the background variability
(Methods). e trend and its signicance are sensitive to estimates
of LUC emissions, which have large uncertainties. We quantied
the impact of LUC uncertainty on the airborne-fraction trend
using a range of LUC estimates (Supplementary Information). For
all nine published LUC estimates considered, the trend in the air-
borne fraction was positive with a signicance level at or above
90%. We conclude that a positive trend in the airborne fraction
is ‘likely’ (66% condence interval), according to the terminology
developed by the IPCC
18
.
A positive trend in the airborne fraction could be explained by
several factors. First, the atmospheric CO
2
concentration could be
increasing on a timescale shorter than those regulating the rate
of uptake of carbon sinks. Second, both the land and ocean CO
2
sinks are expected to decrease in eciency at high ambient CO
2
concentration because of the limits of CO
2
fertilization on land
and the decrease in carbonate concentration, which buers CO
2
in the ocean
19
. ird, the land and/or ocean CO
2
sink could be
responding to climate variability and change. Finally, sink proc-
esses not considered in current models may be contributing to the
observed changes
19
.
Combined evidence from atmosphere and ocean observations
constrains the mean uptake rates of land and ocean CO
2
sinks to
2.6±0.7 and 2.2±0.4 Pg C yr
−1
for 1990–2000, respectively
11,19–22
. We
estimated the year-to-year variability and trends in the land and
ocean CO
2
sinks using a series of global models that represent the
complex processes governing the carbon cycle in these two pools
(Methods). e models were forced by observed changes in global
atmospheric CO
2
concentration and by variable climate elds.
For 2008, the models estimated that the uptake rates for land and
ocean CO
2
sinks were 4.7±1.2 and 2.3±0.4 Pg C yr
−1
, respectively.
e land CO
2
sink was larger (in terms of uptake rate) and the ocean
CO
2
sink was smaller in 2008, relative to the previous three years
(Fig. 2), because the El Niño/Southern Oscillation (ENSO) was in
a positive (La Niña) state in 2008. During La Niña conditions, the
land CO
2
sink is enhanced owing to lower temperatures and wetter
conditions in the tropics, whereas the ocean CO
2
sink is reduced
owing to more intense equatorial upwelling of carbon-rich waters.
Observations in the equatorial Pacic Ocean corroborate the
lower ocean CO
2
sink in 2008 (ref. 23) estimated by the models.
e ocean models also attributed the low ocean CO
2
sink in 2008
in part to a weaker Southern Ocean sink, in response to the con-
tinuing increase in the southern annular mode
24,25
. e model
results over 1980–2006 were broadly consistent with the results
from atmospheric inverse models, which estimate the regional
distribution of air–surface CO
2
uxes using the spatiotemporal
variability in atmospheric CO
2
concentration measurements
26,27
(Supplementary Information).
e land biosphere models showed an increasing global land
CO
2
sink between 1959 and 2008 (Fig. 2c), with large year-to-
year variability. e variability was primarily driven by variability
in precipitation, surface temperature and radiation
28–30
. During
1959–2008, the fraction of the total CO
2
emissions that was absorbed
by the land had no signicant global trend. e ocean models
showed an increasing global ocean CO
2
sink between 1959 and 2008
(Fig. 2d), with small year-to-year variability compared with the land
sink. e modelled CO
2
sink increased at a lower rate than the emis-
sions, and the fraction of the total CO
2
emissions that was absorbed
by the oceans decreased by 0.60±0.15% yr
−1
(Supplementary Table 1)
as a result. e long-term decrease in the fraction of the emissions
taken up by the oceans cannot be veried from ocean observa-
tions alone because of the lack of global data coverage
31
. However,
8
6
4
2
0
1960 1970 1980 1990 20002010
Year
Atmospheric growth
(Pg C yr
–1
)
a
8
6
4
2
0
1960 1970 1980 1990 20002010
Year
Fossil fuel, cement and LUC
emissions (Pg C yr
–1
)
b
2
0
–2
–4
–6
1960 1970 1980 1990 20002010
Year
Land sink (Pg C yr
–1
)
c
2
0
–2
–4
–6
1960 1970 1980 1990 20002010
Year
Ocean sink (Pg C yr
–1
)
d
4
2
0
–2
–4
1960 1970 1980 1990 20002010
Year
Residual (Pg C yr
–1
)
e
Fossil fuel
and cement
Land-use
change
Figure 2 | Components of the global CO
2
budget. a, The atmospheric
CO
2
growth rate. b, CO
2
emissions from fossil fuel combustion and
cement production, and from LUC. c, Land CO
2
sink (negative values
correspond to land uptake). d, Ocean CO
2
sink (negative values
correspond to ocean uptake). e, The residual sum of all sources and sinks.
The land and ocean sinks (c,d) are shown as an average of several models
normalized to the observed mean land and ocean sinks for 1990–2000
(refs 11,19). The shaded area is the uncertainty associated with each
component. See Methods for the sources of data and an explanation
of uncertainties.
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a weakening of the regional CO
2
sinks has been observed since at
least 1990 (Fig. 3), from repeated surface-ocean CO
2
observations
in the North Atlantic Ocean
32,33
and in the Southern Ocean
31,34
, and
from the spatial distribution of atmospheric CO
2
increases in the
Southern Ocean
24
. ese observations suggest that in some ocean
regions, the ocean carbon cycle is responding to climate variability
and climate change in a way that can aect the net uptake of CO
2
by
the ocean. In contrast, increasing air–sea CO
2
ux was observed in
the North Pacic Ocean
35
.
We identied the drivers of the trends in land and ocean CO
2
sinks in the models by forcing a subset of the models with increas-
ing atmospheric CO
2
concentration alone (no changes in climate;
see Supplementary Information). ese additional simulations iso-
late the eect of climate from the combined eects of rapidly rising
CO
2
and high ambient CO
2
concentration. In all models tested,
the land and ocean CO
2
sinks increased at the same rate (in one
model) or faster (in six models) when climate did not change. We
combined the land and ocean CO
2
sinks estimated by the models
with the emissions to reproduce the time evolution of the airborne
fraction. e model-based airborne fraction decreased at a rate of
0.8% yr
−1
when the models were forced by increasing CO
2
concen-
tration alone, and increased at a rate of 0.1% yr
−1
(close to the rate
of 0.3% yr
−1
estimated from observations) when the models were
forced by both increasing CO
2
concentration and changes in climate.
ese simulations do not completely exclude a role for rapidly ris-
ing CO
2
or high ambient CO
2
concentration because the models are
subject to uncertainty, particularly due to their coarse resolution
36
in the ocean and to errors in observed precipitation and radiation
on land.
Our estimates of sources and sinks of CO
2
were based on largely
independent data and methods. us, when all the sources and
sinks were summed every year they did not necessarily add to zero,
because of the errors in the various methods. e sum of all CO
2
sources and sinks, which we call the ‘residual’, spanned a range
of ±2.1 Pg C yr
−1
(Fig. 2e). is residual was not explained by the
atmospheric CO
2
growth rate, the CO
2
emissions from fossil fuel
combustion or the ocean uptake, because the uncertainties in these
components were much smaller than the variability of the resid-
ual. Errors in LUC ux may explain a small part of the residual,
for instance during the late 1990s, when res in Indonesia were
partly caused by land clearance taking advantage of the drought
conditions
17
. Our re-based LUC anomalies for 1997 were 0.7 Pg C
greater than normal and account for one-half of the residual for
that year. Overall, the residual was most probably caused by the
regional responses of terrestrial vegetation to climate variability,
indicating that land models overestimated the response of vege-
tation to the relatively cool/wet La Niña-like climatic conditions
of the mid 1970s and underestimated the response to the vol-
canic eruption of Mount Pinatubo, in the Philippines, in the early
1990s. is later underestimation has been explained elsewhere
as resulting from a missing response in the models to the aerosol-
induced increase in the diuse-light component of surface irradi-
ance, and the subsequent enhancement of light penetration into
vegetation canopies
29
.
As a result of all CO
2
sources and sinks, atmospheric CO
2
growth
was 3.9±0.1 Pg C yr
−1
in 2008, an increase of 1.8 ppm, which is
0.6 Pg C yr
−1
less than the average of the previous three years despite
there being an increase in CO
2
emissions from fossil fuel combus-
tion. Average atmospheric CO
2
in 2008 reached a concentration of
385 ppm, which is 38% above pre-industrial levels. e lower-than-
average atmospheric growth rate was probably driven by a high
land CO
2
uptake due to the La Niña state of ENSO, and by reduced
rates of deforestation in southeast Asia and in the Amazon
16
, as
indicated by lower rates of re and clear-cut activities measured at
the deforestation frontier.
Filling the gaps in the global CO
2
budget
Progress has been made in monitoring the trends in the carbon
cycle and understanding their drivers. However, major gaps
remain, particularly in our ability to link anthropogenic CO
2
emissions to atmospheric CO
2
concentration on a year-to-year
basis; this creates a multi-year delay and adds uncertainty to
our capacity to quantify the eectiveness of climate mitigation
policies. To ll this gap, the residual CO
2
ux from the sum
of all known components of the global CO
2
budget needs to
be reduced, from its current range of ±2.1 Pg C yr
−1
, to below
the uncertainty in global CO
2
emissions, ±0.9 Pg C yr
−1
. If this
can be achieved with improvements in models and observing
systems, geophysical data could provide constraints on global
CO
2
emissions estimates.
e likely recent trend in the airborne fraction of the total
emissions suggests that the growth in uptake rate of CO
2
sinks is not
keeping up with the increase in CO
2
emissions
11
. e models used
here indicate that this trend could be due to the response of the land
and ocean CO
2
sinks to climate variability and climate change. If the
model response to recent changes in climate is correct, this would
lend support to the positive feedback between climate and the car-
bon cycle that was predicted by many coupled climate–carbon cycle
models
37
. However, these models do not yet include many processes
and reservoirs that may be important, such as peat, buried carbon
in permafrost soils, wild res, ocean eddies and the response of
marine ecosystems to ocean acidication. An improved knowledge
of regional trends would help to constrain the climate–carbon cycle
feedback better.
e current growth in global anthropogenic CO
2
emissions is
tightly linked to the growth in GDP. On the basis of the projected
changes in GDP, it is likely that CO
2
emissions in 2009 will revert to
their 2007 levels. e key to sustained emissions reductions aer the
global economy recovers lies in restructuring the primary energy
use to decouple emissions from GDP
12
.
Methods
Original data to complete the global CO
2
budget are generated by multiple agen-
cies and research groups around the world and are collated annually by the Global
Carbon Project (http://www.globalcarbonproject.org). CO
2
emissions from fossil
fuel and other industrial processes between 1959 and 2006 were based on United
Nations Energy Statistics and cement data from the US Geological Survey
38
, and
were provided by the Carbon Dioxide Information Analysis Center. For 2007 and
2008, increases in fossil fuel emissions were calculated using BP energy data
39,40
and
increases in cement emissions were based on the preliminary data
41
on 20 of the
largest producers (amounting to over 80% of total global production), assuming
120˚ E 180˚ 120˚ W 60˚ E
60˚ N
30˚ N
30˚ S
60˚ S
0˚
0˚60˚ W
A
B
2.0
0.3
0.1
–0.1
–0.3
–2.0
Sea–air CO
2
trend (μatm yr
–1
)
Longitude
Latitude
Figure 3 | Trends in the observed partial pressure of CO
2
for ocean minus
air, for 1981–2007. The observed trends are calculated by fitting a linear
trend to repeated measurements of surface-ocean and air CO
2
as in refs 31
and 32. Positive (red) values indicate regions where the partial pressure of
CO
2
in the ocean is increasing faster than atmospheric CO
2
. Large, medium
and small dots are plotted for trends with errors of <0.25, 0.25–0.50 and
>0.50 matm yr
−1
, respectively. In southern circumpolar waters (A), the
trends were estimated from austral winter data
31
. In the South Indian Ocean
(B), the trends were estimated for 1991–2007 (ref. 34) only.
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NATURE GEOSCIENCE DOI: 10.1038/NGEO689
the same fractional change as in 2005–2006 for smaller producers. e gas-aring
emissions for 2006 were also used for 2007 and 2008. Per-capita emissions were
compiled by the Carbon Dioxide Information Analysis Center between 1959 and
2006. For 2007 and 2008, per-capita emissions were based on our global CO
2
emis-
sions and world population from the US Census Bureau. We used an uncertainty in
CO
2
emissions of ±6% (ref. 42), representing a 1σ (66%) condence interval. is
uncertainty was revised upwards from the 5% used in ref. 11 beccause of the larger
share of global emissions from non-Annex B countries.
We calculated CO
2
emissions from LUC using a book-keeping method
13
with
the revised statistical data from the Food and Agriculture Organization of the
United Nations Global Forest Resource Assessment
43
, as in ref. 11. We used re
emissions estimates from the Oak Ridge National Laboratory Distributed Active
Archive Center’s Global Fire Emissions Database, version 2, where information
on burned area and re activity from various satellite sensors
44
is combined with
a biogeochemical model to estimate carbon stocks and combustion parameters
45
.
We sampled only those 1° × 1° grid cells undergoing active deforestation during
the 2000–2005 period, using existing maps
46
. Emissions from the ‘maintenance
res’ (for example pasture burning) at the deforestation frontier are probably
an order of magnitude lower than deforestation emissions because of lower fuel
loads in pasture and cropland ecosystems
45
; in our analyses, we therefore included
90% of the total estimated emissions. e use of re estimates assumes that
year-to-year changes in re CO
2
emissions were the main cause of interannual
variability in LUC emissions and that the delayed emissions from decomposition
were relatively constant. e variability in LUC estimated from re emissions
correlated with the variability estimated by the book-keeping method when
they overlap (correlation coecient, r = 0.54; n = 12). We used an uncertainty of
±0.7 Pg C yr
−1
, representing a 1σ (66%) condence interval. is uncertainty was
revised upwards from the ±0.5 Pg C yr
−1
used in ref. 11, to acknowledge recently
identied inconsistencies between deforestation and agricultural conversion
statistics (see Supplementary Information).
e data on annual growth in atmospheric CO
2
concentration was provided
by the US National Oceanic and Atmospheric Administration Earth System
Research Laboratory (http://www.esrl.noaa.gov/gmd/ccgg/trends). We used the
global mean data aer 1980 and the Mauna Loa data between 1959 and 1980.
e land CO
2
sink was estimated using ve global vegetation models updated
from ref. 28 (see Supplementary Information). e models represent the proc-
esses governing ecosystem carbon dynamics in biomass, litter and soil pools and
the space–time distribution of CO
2
uxes exchanged with the overlying atmos-
phere. All models were forced by observed atmospheric CO
2
concentration and a
combination of meteorological elds from the Climatic Research Unit observed
climate data and the US National Centers for Environmental Prediction reanalysis
product
47
. e ocean CO
2
sink was estimated using four ocean general circulation
models coupled to ocean biogeochemistry models
24,48–50
. e models represent
the physical, chemical and biological processes governing the marine carbon
cycle and the space–time distribution of CO
2
uxes exchanged with the overlying
atmosphere. All models were forced by meteorological elds from the US National
Centers for Environmental Prediction reanalysis product
47
. e land and ocean
CO
2
sinks were estimated from the mean of all models. We corrected the model
mean to agree with the observed uptake rates for land and ocean CO
2
sinks in
1990–2000 (refs 11,19). us, the models were used to assess the year-to-year
variability and trends in the land and ocean CO
2
sinks only. e uncertainty for a
given time period combined the uncertainty for 1990–2000 (ref. 19) and ±1 mean
absolute deviation for all models around the central model estimate for the given
period (see Supplementary Information).
e signicance of the trend in airborne fraction was computed from the
monthly deseasonalized atmospheric CO
2
data as detailed in ref. 11. e noise
in the airborne fraction was reduced by removing the part of the variability
associated with the ENSO and volcanic-activity indices. e statistical signi-
cance was computed from a 1,000-member Monte Carlo simulation with noise
properties similar to those of the airborne fraction. e standard deviation of the
1,000-member simulation provided the uncertainty in the results.
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