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\title{Brief Article}
\author{The Author}
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{\vskip 12pt}
{\noindent Section 3.4}
{\vskip 12pt}

{\noindent The Impact of IPCC Scenarios}
{\vskip 12pt}

We use the simulation results generated using the IPSL "Earth system model"
(Marti, et al, 2006) as external ocean surface forcing fields for IPCC scenario experiments.
The IPSL-CM4 version of the model couples four components of the Earth system.
LMDZ is the component for atmospheric dynamics and physics. 
ORCA is the component for ocean dynamics. LIM is the component for sea-ice dynamics
and thermodynamics. ORCHIDEE handles the land surface.

The atmospheric parameters needed to force the ORCA2\_LIM\_PISCES configuration of 
NEMO are described in Sec 3.2.
%% zonal and meridional wind components at 10m above the surface, 
%% temperature and specific humidity at 2m above the surface,
%% snow falling and precipitation rates, downwelling shortwave and longwave at the surface.
Daily and monthly values of the parameters are avaialble for the following climate scenario
simulations on a 96 x 71 longitude-latitude grid. 
All scenario simulations are started with the same procedure. 
The ocean starts from rest with temperature and salinity set to the values of 
the Levitus (1982) atlas. The sea-ice characteristics correspond to a ten years adjustment 
of the sea-ice model from a forced ocean-ice simulation. The atmosphere is initialized from 
the ECMWF (ERA15) for 1 Jan 1979. For more details, see Marti, et al (2006).
With this procedure, the first ten years of the simulation correspond to rapid adjustments 
between all the models, and they are not representative of the longer time scale evolution
of the simulation. We'll discard these first ten years of the IPSL-CM4 simulation results as 
the atmospheric forcing for our climate scenario runs using the NEMO ORCA2\_LIM\_PISCES.

Simulation results of the following climate scenarios will be used to
force the NEMO system to generate corresponding biogeochemical tracers.

"2L20" is a control simulation with concentration of the different trace gazes
prescribed to modern trace gazes concentration (the simulation period 1840-2409).
%% what are "modern trace gazes concentration"? constant in time?

"2L26" is an A2 emissions scenario simulation for 2000-2100.

In the A2 emissions scenario, cumulative CO2 emissions by the middle and end of the 21st century 
are projected to be about 600 and 1850 GtC respectively, and expected CO2 concentrations for the 
middle and end of the 21st century in this scenario are about 575 and 870 ppm, respectively. The 
current concentration of CO2 is about 380 ppm (Nakicenvoic et al., 2000).
%% Methane and nitrous oxide increases grow rapidly in the 21st century.
%% Sulfur dioxide increases to a maximum value just before 2050 (105 MtS/yr) and
%% then decreases in the second half of the century (60 MtS/yr by 2100) 
%% (Nakicenvoic et al., 2000).
The full set of IPCC simulations performed at IPSL are described at http://mc2.ipsl.jussieu.fr/simules.html.

{\vskip 12pt}
{\noindent EXP 1: Reference run}
{\vskip 12pt}

We'll use "2L20" surface forcing datasets to run the ORCA2\_LIM\_PISCES 
for the period 1850 to 2100 to generate a control simulation of biogeochemical parameters
for that period. For inital state of the model at the beginning of the simulation
(01Jan1850), we'll use one or more passes through the 1850 to 1859 forcing as spinup.

{\vskip 12pt}
{\noindent EXP 2: A2 emissions scenario run}
{\vskip 12pt}

Using "2L26" dataset, we'll run the ORCA2\_LIM\_PISCES for the period 2010 to 2100.
For the initial condition, the restart conditions at the end of 2009 in the EXP 1 will be used.
Model outputs from EXP 1 and EXP 2 are compared for the period 2010-2100.
We're particularly interested in the differences in total chlorophyll pigment concentration 
(Chl), SST, mixed-layer depth (MLD), and sea-ice concentration (and pCO2) in the Arctic.

A recent observational study suggests that phytoplankton biomass has declined
a global rate of ~1\% of the global median per year over the past century
(Boyce, et al, 2010). SST was the strongest single predictor of Chl.
Rising SSTs over most of the global ocean were associated with
declining Chl in eight out of the ten regions.
Positive relationships between SST and Chl were found in the Arctic and 
Southern regions while negative effects prevailed at low latitudes.
Latitudinal gradients in MLD effects were also observed, with predicted positive 
effects between 20N and 20S and negative effects in polar areas, suggesting that 
warming SST and reduced MLD may be responsible for phytoplankton declines at low latitudes.

We'll investigate whether three variables, SST, Chl and MLD in the model 
simulation resutls also suggest  the coupling between physical climate variability 
and the Chl concentration in the upper ocean as found in a recent study of the observed data.
We'll also investigate whether simulated global phytoplankton concentration will decline over the
next  century and if so whether long-term declining trends are related to increasing  SST as they
are found in the observed data over the past century (Boyce, et al, 2010).

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EXP 3: 1%CO2 2xCO2 sceanrio ???
???
"2L23", "2L23B" 

"2L24" is a pre-industrial simulation with trace gazes concentration
prescribed to pre-industrial values (circa 1750) (1931-2080).

"2L23" is a CMIP simulation with 1% increase in the CO2 concentration
until quadrupling CO2 is reached (1931-2080).

"2L23B" is an additional stabilization scenario with 2xCO2 
starting from the CMIP run when the corresponding level of CO2 is reached (1931-2080).

"2L26" and "2L27" are emissions scenarios A2 and A1B respectively for 2000-2100.

"2L28" and "2L31" are emissions scenario B1 for 2000-2100.

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We observe declines in eight out of ten ocean regions, and estimate a global rate of decline of 
~1\% of the global median per year. Our analyses further reveal interannual to decadal 
phytoplankton fluctuations superimposed on long-term trends. These fluctuations are strongly 
correlated with basin-scale climate indices, whereas long-term declining trends are related to 
increasing sea surface temperatures. We conclude that global phytoplankton concentration has 
declined over the past century; this decline will need to be considered in future studies of marine ecosystems, geochemical cycling, ocean circulation and fisherie



The A2 story line is characterized by heterogeneity. Self reliance and local identities are emphasized, and population increases continuously. Population reaches over 10 billion by 2050. Economic development is regionally oriented and economic and technological development is relatively slow, compared to the other story lines. From these major factors, and using Integrated Assessment Models (IAMs), emissions of the major greenhouse gases were developed for the 21st century. 

Cumulative CO2 emissions by the middle and end of the 21st century are projected to be about 600 and 1850 GtC respectively, and expected CO2 concentrations (in parts per million, ppm) for the middle and end of the 21st century in this scenario are about 575 and 870 ppm, respectively. The current concentration of CO2 is about 380 ppm. Methane and nitrous oxide increases grow rapidly in the 21st century. Sulfur dioxide increases to a maximum value just before 
2050 (105 MtS/yr) and then decreases in the second half of the century (60 MtS/yr by 2100).





