Equilibrium sensitivity of global terrestrial ecosystem carbon to elevated nitrogen b
l
d i
deposition in CLM4.0 of NCAR
Email: [email protected]
CLM4 N-deposition
0.12 gN/m2 (~20 Tg-N/yr)
0 43 gN/m2 ((~73
0.43
73.1
1 Tg-N/yr)
Galloway et. al. 2004,2008 says y
,
y
• Humans have more than doubled the rate at which nitrogen enters the
the rate at which nitrogen enters the
terrestrial biosphere ¾ Agricultural land expansion, Agricultural land expansion
¾ Fossil fuel burning and ¾ Fertilization application
Thus, Earth’s vegetation cover affects significantly
0 48 gN/m2 (~81.6
0.48
( 81 6 Tg
Tg-N/yr)
N/yr)
¾Alter regional and global climate through
changes in the global carbon and nitrogen cycles
¾ To date, very few global scale studies exist
on the impact of elevated nitrogen deposition
on terrestrial ecosystem
For present day
Bonan
& Levis
B
L i 2010
Annual mean net exchange of carbon
Net emission to atmosphere
With CO2 fertilization
Net sink by the
biosphere
Jain et al 2009, GBC
The influence of nitrogen on
concentration-carbon
concentration
carbon feedback is of
greater importance
• How much ecosystem carbon is sequestered per unit increase in N‐
dep (per Tg‐N)? • How is the Terrestrial ecosystem carbon sensitivity to N‐dep
responds to the changing climate (per K) and CO2 concentration responds to the changing climate (per K) and CO
concentration
(per ppm)?
Description of CLM4
The CLM4 examines the physical
physical, chemical
chemical,
and biological processes of terrestrial
ecosystem and demonstrates the importance of
climate in determining vegetation compositions
and the feedback.
1000-year experiments (Net ecosystem exchange is is nearly zero by 900)
A horizontal resolution of 1.9° latitude and 2.5° longitude is used. A 57-year (1948–2004)
observational atmospheric forcing dataset is used to drive the model.
model
set 1
CTL
2N
4N
8N
set2
CTL2xCO2
2N2xCO2
4N2xCO2
8N2xCO2
set3
CTL2K ((Pre-industrial N-deposition)
p
)
2N2K
4N2K (Present day N-deposition)
8N2K (by 2100)
Increased BNF and C-fixation
8%
5.7%
3.5%
15.6%
15.67%
15.75%
15 9%
15.9%
Pool size effect: at
higher N-dep levels, the
carbon stocks are
higher and hence the
change per unit
warming is larger
33%
32.4%
32.2%
32.3%
To find the TEC Sensitivity
Following Bala et al 2012, Climate Dynamics)
The carbon
Th
b storage
t
sensitivity
iti it over land
l d (βL) to
t CO2 is
i defined
d fi d as the
th change
h
in TEC associated with unit change in atmospheric CO2
ΔTEC
βL =
ΔCa
The carbon storage sensitivity over land to temperature change (γL) as the
change in TEC associated with unit change in temperature
ΔTEC
γL =
ΔT
We have defined the carbon storage sensitivity over land to N-dep as the
change in TEC associated with unit change in atmospheric N-dep and
denoted as δL
ΔTEC
δL =
ΔN
Sensitivity of TEC
3.41
2 83
2.83
2.08
Pre-industrial
ese day
Present
21st Century
ΔTEC
δL =
ΔN
YEAR
CO2 fertilization
236 Gt-C is taken up by
terrestrial ecosystem
Climate Warming
g
152 Gt-C is lost by terrestrial
ecosystem
N- deposition
p
175 Gt-C is taken up by
terrestrial ecosystem
y
Total Ecosystem Carbon (TEC) sensitivity
βL
γL
δL
(Gt-C/ppm) (Gt-C/K)
CTL
2N
4N
8N
2.21
2.30
2.43
2 67
2.67
-152
-158
-167.7
-182
182
(Gt-C/Tg-N)
Nfertilizati
on
3.41
2.83
2 08
2.08
With
2xCO2
With 2K
4.48
3.82
2 92
2.92
2.79
2.34
1 71
1.71
βL =
ΔTEC
ΔCa
γL =
ΔTEC
ΔT
δL =
ΔTEC
ΔN
During the years 1765 – 2000 (Jain et al 2009 and Galloway et al 2004)
Due to N-fertilization (51.4TgN):
175 Gt-C is taken up by terrestrial ecosystem
Due to CO2 fertilization (110ppm): 236 Gt-C is taken up by terrestrial ecosystem
Due to Warming (~1 deg C) :
152 Gt-C is lost by terrestrial ecosystem
Conclusions
•
Our simulations suggest that both CO2‐ and N‐fertilization lead to enhanced TEC – with TEC increasing by 2.21 Gt‐C per ppm increase in atmospheric CO2
concentration and by 3.41 Gt‐C per unit increase in N‐deposition (Tg‐N).
•
y
p
g
TEC decreases by 152 Gt‐C per unit warming •
Based on these sensitivities, we estimate that the TEC losses due to increased warming are likely compensated by the additional nitrogen deposition since the
warming are likely compensated by the additional nitrogen deposition since the preindustrial times (176Gt‐C verses 152 Gt‐C)
•
The magnitude of TEC sensitivity decreases beyond current N‐deposition levels, The
magnitude of TEC sensitivity decreases beyond current N deposition levels
indicating N‐deposition in the future may not be able to compensate the climate warming effect
for y
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