3. The Impact of IPCC SRES Scenarios In our emissions scenario experiments with the NEMO ORCA2_LIM2_PISCES model, we use for external ocean surface forcing fields the results of the simulations performed using the IPSL "Earth system model" (Marti, et al, 2006). The simulations were carried out following Special Report on Emission Scenarios (SRES) emissions scenario (IPCC, 2001, 2007). [All SRES emissions scenario simulations generated using the IPSL-CM4 model were initialized with the model conditions at the end of the 20C3M simulation (1860 to the end of 2000) and were run to 2100.] 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_LIM2_PISCES configuration of NEMO include wind stress components, short- and longwave radiation, temperature, humidity, and precipitation. 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 emmissions scenario simulations. Datasets we used can be downloaded from https://esg.llnl.gov:8443/index.jsp or http://dods.ipsl.jussieu.fr/mc2ipsl/calculo/. Detailed model initialization procedures of SRES scenario experiments with IPSL-CM4 are described in Marti, et al (2006). We plan to perform the following (four) SRES scenario experiments. EXP 1: Reference run for 1961-2000. (20C3M) We run a 40-year NEMO ORCA2_LIM2_PISCES control simulation for 1961-2000 using outputs from the IPSL simulation labeled "Climate of the 20th century experiment (20C3M)" run from 1860 to 2000 that was driven by the estimate of the known historical radiative forcing agents which include greenhouse gases (CO2, CH4, N2O, CFCs) and sulfate aerosol direct effects. The results of 20C3M represent the state of the current atmopsheric environment with greenhouse gases increasing as obserevd through the 20th century. The external forcings used in this 20C3M experiment are: -daily zonal and meridional wind components at 10m above the surface -daily air temperature at 2m above the surface -monthly downwelling shortwave and longwave at the surface -monthly snow falling and precipitation rates -monthly specific humidity at 2m above the surface. Spinup: One pass through the 1958-2007 forcing with the CORE.2 dataset was used as a spinup for the 20C3M simulations beginning at 01Jan1961. In this “spin-up” run, the ocean is initially at rest with temperature and salinity set to January climatorogical values of Levitus (1982). In the Arctic and Southern Oceans, initial mean sea ice thickness of 3.5 m is imposed in regions with a sea surface temperature below 0 C. An initial ice concentration of 0.95 are also assumed (Vancoppenolle, et al, 2009). Initial biogeochemical parameters are also set following Aumont and Bopp (2006). From this initial state, the ORCA2_LIM2_PISCES configuration of NEMO is integrated for 50 years with Newtonian restoring terms for sea surface salinity only. For the ocean surface forcing, the CORE bulk formula is used with the 50-year CORE.2 dataset. --CORE.2 Global Air-Sea Flux dataset and various climatologies are available from NCAR along with NCEP/NCAR daily reanalysis data [Large and Yeager, 2004; (http://dss.ucar.edu/datasets/ds260.2/)]. The results from this experiment represent the present state of biogeochemical parameters and will be compared to the results from emissions scenario simulations described below. We focus on (three) SRES scenarios for which IPSL simulation results are available. EXP 2: SRES A1B emissions scenario simulation for 2001-2050. 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. In particular, the A1B scenario is characterized by "balanced across all evergy sources" not relying too heavily on one particular energy source. 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). The external forcings used in this A1B experiment are: -monthly zonal and meridional wind components at 10m above the surface -monthly air temperature at 2m above the surface -monthly specific humidity at 2m above the surface. -monthly downwelling shortwave and longwave at the surface -monthly snow falling and precipitation rates. For the initial conditions in EXP 2 (A1B), the restart conditions at the end of 2000 in the reference run EXP 1 (20C3M) were used that include restart conditions of biogeochemical parameters. Model output: Model outputs from SRES experiment EXP 2 for the 20-year period 2031-2050 and the reference EXP 1 for the period 1981-2000 are compared. *========================================================================================= *========================================================================================= EXP 3: SRES A2 emissions scenario simulation for 2001-2100. 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. 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). All SRES emissions scenario simulations generated using the IPSL-CM4 model were initialized with the model conditions at the end of the 20C3M simulation (1860 to the end of 2000) and were run to 2100. For the initial conditions in EXP 2 (A1B), the restart conditions at the end of 2000 in the reference run EXP 1 (20C3M) were used that include restart conditions of biogeochemical parameters. *========================================================================================= Scenario descriptions are based on those in AR4 and TAR. The A1 scenarios are of a more integrated world. The A1 family of scenarios is characterized by: * Rapid economic growth. * A global population that reaches 9 billion in 2050 and then gradually declines. * The quick spread of new and efficient technologies. * A convergent world - income and way of life converge between regions. Extensive social and cultural interactions worldwide. There are subsets to the A1 family based on their technological emphasis: * A1FI - An emphasis on fossil-fuels (Fossil Intensive). * A1B - A balanced emphasis on all energy sources. * A1T - Emphasis on non-fossil energy sources. -- IPCC's Third Assessment Report (TAR) and Fourth Assessment Report (AR4) *----------------------------------------------------------------------------------------- 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 Chlorophyll (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 from 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 (Behrenfeld, 2006, Boyce, et al, 2010). *========================================================================================= * http://www.ipcc-data.org/ddc_co2.html * http://www-pcmdi.llnl.gov/ipcc/standard_output.html#Experiments * http://dods.ipsl.jussieu.fr/mc2ipsl/calculo/2L23B/Atm/TS/ * http://dods.ipsl.jussieu.fr/mc2ipsl/calculo/