3.4 The Impact of IPCC SRES Scenarios We use Special Report on Emission Scenarios (SRES) emissions scenario simulation results generated using the IPSL "Earth system model" (Marti, et al, 2006) for external ocean surface forcing fields in our emissions scenario experiments with the NEMO ORCA2_LIM3_PISCES model (IPCC, 2001). The Earth system model IPSL-CM4 is a modular suite of four model components of the Earth system that can be used to study the complex interactions between the atmosphere, the ocean, sea-ice, land surfaces and glaciers. The model does not include a separate biogeochemical component. The full set of IPCC emission scenario simulations performed at IPSL are described at http://mc2.ipsl.jussieu.fr/simules.html. The atmospheric parameters needed to force the ORCA2_LIM3_PISCES configuration of NEMO are described in Sec 3.2. Daily and monthly values of these parameters produced with the IPSL-CM4 model are available on a 96 x 71 longitude-latitude grid (2.5 deg x 3.75 deg) for various emmisions scenario simulations. Detailed model initialization procedures of SRES scenario experiments with IPSL-CM4 are described in Marti, et al (2006). EXP 1: Reference run for 1950-2000. We'll run a NEMO ORCA2_LIM3_PISCES control simulation using outputs from the IPSL simulation labeled climate of the 20th century experiment (20C3M) run from 1860 to 2000 that is driven by the estimate of the known historical radiative forcing agents which include greenhouse gases (CO2, CH4, N2O, CFCs) and sulfate aerosol direct effects. For details of radiative forcings, see online http://www-pcmdi.llnl.gov/ipcc/model_documentation/IPSL-CM4.pdf. We focus on three SRES scenarios for which IPSL simulation results are available. EXP 2: SRES A1B emissions scenario simulation for 2001-2100. (2L27) The A1 storyline and scenario family describes a future world of very rapid economic growth, global population that peaks in mid-century and declines thereafter, and rapid introduction of new and more efficient technologies. The A1B scenario is characterized by "balanced across all evergy sources" not relying too heavily on one particular energy source. EXP 3: SRES A2 emissions scenario simulation for 2001-2100. (2L26) The A2 scenario describes a very heterogeneous world with continuously increasing global population and regionally oriented economic growth that is more fragmented and slower than in other storylines. It is characterized as "business-as-usual." EXP 4: SRES B1 emissions scenario simulation for 2001-2100. (2L28) The B1 scenario describes a convergent world with rapid changes in economic structures toward a service and information economy, with reductions in material intensity, and the introduction of clean and resource-efficient technologies. It is characterized as "the most environmentally conscious." In the A1B, A2 and B1 emissions scenarios, expected global mean CO2 concentrations for the end of the 21st century are about 720, 860, and 550 ppm, respectively. The current concentration of CO2 is about 380 ppm. Those concentration levels translate into the following global average surface air temperature increases relative to 1990: under scenarios A1B, A2 and B1 2.95, 3.79, and 1.98 deg C,respectively, by the end of the 21st century (IPCC, 2001). In the Arctic region, under the A2 (and B2) emissions scenarios, the models projected that mean annual Arctic surface temperatures north of 60 N will be 2 to 4 C higher by mid-century and 4 to 7 C higher toward the end of the 21st century (Fig. 18.4), compared to the present. Under scenarios of climate warming, sea-ice cover is expected to “retreat” further into the Arctic Basin, to breakup earlier and freeze-up later, and to become thinner and more mobile (ACIA, 2005). ACIA, 2005: Arctic Climate Impact Assessment, Cambridge, New York, N.Y. : Cambridge University Press, 2005. 1046 p. All SRES emissions scenario simulations we plan to use were initialized with the model conditions at the end of the 20C3M simulation (through the end of 2000) and run to 2100. For the initial conditions in our EXPs 2-4, the restart conditions at the end of 2000 in the reference run (EXP 1) will be used that include restart conditions of biogeochemical parameters. ------------------------------------------------------------------------------------------ Model outputs from SRES experiments EXPs 2-4 and reference EXP 1 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 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 our model simulation resutls of the SRES emission scenario experiments also show the coupling between physical climate variability and the Chl concentration in the upper ocean as found in the obervational 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 are found in the observed data over the past century (Boyce, et al, 2010).