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TRINITY
COLLEGE
DUBLIN
Future atmospheric conditions increase the
greenhouse-gas intensity of rice cultivation
K.J. van
,†
Groenigen* ,
Introduction
 Heterogeneity in CH4 fluxes makes it difficult
to determine their global response to elevated
CO2 and warming from individual studies.
 We used meta-analysis to summarize the effect
of elevated CO2 and warming on CH4 emissions,
rice yield and yield-scaled CH4 emissions.
aa
(27)
(184)
Effect of warming (% per 1° C)
 Growing global food demand argues for
assessing GHG emissions from croplands on the
basis of yield rather than land area5.
80
(23)
70
60
50
40
30
20
10
0
CH4
Yield
0.4
 Data were analyzed using the natural log of the
response ratio (lnR) as the effect size. Warming
effects were normalized for the degree of
temperature increase. The lnR values were
weighted by replication. Bootstrapping was used
to calculate 95% confidence intervals on mean
effect size estimates. Average effect sizes were
back-transformed and reported as % change to
ease interpretation.
© by M. Schneider
Chinese rice paddies. Photo credit: Jim Hill, UC Davis.
bb (42)
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(109)
15
10
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0
-5
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-10
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-25
CH4
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a
0.2
lnRTN yield
 We extracted results for CH4 emissions and
rice yield from CO2 enrichment and warming
studies, conducted in the field or indoors. For
studies in which CH4 emissions and rice yield
were both reported, we also calculated yieldscaled CH4 emissions.
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Yield
Yield-scaled Root
CH4
biomass
The correlation between control temperature and treatment effects
on yield and yield-scaled CH4 emissions in warming studies (Fig.
2) suggests that effects of warming will intensify as global
temperatures continue to rise. It also corroborates model
predictions that climate warming will affect rice yields in tropical
regions more strongly than in temperate regions8.
Besides CH4, nitrous oxide (N2O) is an important GHG emitted
from rice paddies. However, N2O on average account for only
11% of the global warming potential of GHG emissions from rice
paddies9. This suggests that N2O will play a minor role in changing
the future GHG intensity of rice cultivation.
Figure 1. Results of a meta-analysis on the response of CH4 emissions, yield and yield-scaled CH4 emissions
from rice paddies to increased levels of atmospheric CO2 and warming. a Effects of increased CO2. b Effects of
warming. The number in parentheses indicates the number of observations used in each meta-analysis. Error
bars, 95% confidence intervals.
0.0
Materials and methods
contact: [email protected]
Discussion
Yield-scaled
CH4
lnRTN yield-scaled CH4
 Rice cultivation is a major source of the potent
GHG methane3 (CH4) and rice is the world’s
second-most produced staple crop4.
B.A. Hungate*
Results
Effect of increased CO2 (%)
 Rising atmospheric CO2 and global warming
are expected to affect rice yields and greenhouse
gas (GHG) emissions from rice paddies1,2.
C. van
‡
Kessel ,
-0.2
-0.4
-0.6
-0.8
-1.0
r2 =
-1.2
0.30
p < 0.01
-1.4
15
20
30
Control temperature (°C)
35
http://hostgk3.biology.tohoku.ac.jp/English%20Page/Riceface.html
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0.0
-0.2
© IRRI Images
Temperature
controlled open
top chambers
to study the
effect of
warming on
rice yield.
Conclusions and future research
0.4
-0.4
25
b
The FACE (Free
Air Carbon
Enrichment)
experimental
site in
Shizukuishi,
Japan.
r2 = 0.45
p = 0.01
15
20
25
30
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Control
Control temperature
temperature(°C)
(°C)
Figure 2. Effects of warming on rice yield and yield-scaled CH4 emissions vs. control temperatures in warming
experiments. a, The normalized effect of warming on rice yield (lnRTN) vs. control temperature in the warming
experiment. b, The normalized effect of warming on yield-scaled CH4 emissions (lnRTN) vs. control temperature.
 Fig. 1a: Elevated CO2 significantly increased CH4 emissions (+42%), rice yield
(+25%) and yield-scaled CH4 emissions (+31%). b: Warming significantly
decreased yield (-15% per 1°C) and increased yield-scaled CH4 emissions (+12%
per 1°C).
 Fig. 2: The negative effect of warming on rice yield (a) and the positive effect on
yield-scaled CH4 emissions (b) increased with the control temperature of warming
studies.
 Within studies that applied warming and CO2 enrichment in a factorial design,
we found no interactive treatment effects on either yield, CH4 emissions, or yieldscaled CH4 emissions (data not shown, see ref. 6 for details).
 Climate models estimate that by the end of the 21st century, land temperatures
in rice growing regions will be 4°C warmer than today7. Since we found no
significant interactions between warming and CO2 we calculated their combined
effect by multiplying their average treatment effects. Using this approach, 4°C
warming with CO2 enrichment will increase CH4 emissions by 58%, decrease rice
yields by 34% and increase yield-scaled CH4 emissions by 106%.
Future CH4 emissions from rice paddies will mostly increase due to
rising atmospheric CO2 and less due to warming, but both factors
contribute to an increased GHG intensity of rice cultivation.
Compared with other cereals, rice production systems show a
large potential for reduction in CH4 emissions through management
practices9. Moreover, adaptation efforts can reduce the negative
effect of warming on rice yields10. Future research should assess
whether these mitigation and adaptation efforts interact with global
change factors to influence CH4 emissions from rice agriculture.
Acknowledgements
Funding was provided by the NSF (DEB-0949460), the DOE Office of Science (BER)
through the Western Regional Center of NICCR, and the Irish Research Council, co-funded
by Marie Curie Actions under FP7.
References
This poster is based on our recent article in Nature Climate Change6.
1. Van Groenigen KJ et al. Nature 475, 214-216 (2011).
2. Peng S et al. PNAS 101, 9971-9975 (2004).
3. US-EPA. Global Anthropogenic non-CO2 GHG emissions: 1990-2020 (2006).
4. http://faostat.fao.org/site/567/default.aspx#ancor.
5. Cassmann KG et al. Annu. Rev. Environ. Resour. 28, 315-358 (2003).
6. Van Groenigen KJ et al. Nature Climate Change, doi:10.1038/nclimate1712 (2012).
7. Meehl GA et al. in Climate Change 2007: The Physical Science Basis (eds Solomon S
et al.) 747-845 (Cambridge Univ. Press, Cambridge, 2007).
8. Easterling WE et al. in Climate Change 2007: The Physical Science Basis (eds Parry M
et al.) 273-313 (Cambridge Univ. Press, Cambridge, 2007).
9. Linquist B et al. Glob. Change Biol. 135, 10-21 (2012).
10. Wassman R et al. Adv. Agron. 102, 91-133 (2009).
* Department of Biological Sciences, Northern Arizona University, Flagstaff, USA
† Department of Botany, Trinity College, Dublin, Ireland
‡ Department of Plant Sciences, University of California, Davis, USA.