Resumen de Coupling socioeconomic processes with climate models: a parameterization for the community earth system model (cesm)
Andrés Navarro Martínez de la Casa
Earth System Models (ESMs) are powerful tools for understanding Earth’s climate. In short, they consist in a set of equations that summarize the main physical and biogeochemical processes of the Earth. These models aim to simulate the complex interactions of the atmosphere, ocean, land surface, and cryosphere, together with the carbon and nitrogen cycles.
Despite the advance in climate modeling, the inclusion of dynamical interactions of the socioeconomic dimension into global models is an underexplored field. Thus, most of the ESMs treat processes and fluxes of the anthroposphere as an uncoupled external forcing that feed the model. One reason is theoretical, as the feedbacks are considered of second-order importance. Another reason is the limited availability of computing power. However, advances in computational resources now allow to parameterize human-Earth processes in a more detailed way.
A relevant human-induced activity in climate models is the anthropogenic fossil fuel emissions. The most typical way to include this process in ESMs is prescribing global CO2 concentrations on the assumption that the gas soon becomes well-mixed in the atmosphere. However, given the highly non-linear character of the processes involved, it is not unreasonable to assume that geographical variability of anthropogenic emissions may affect global climate.
This thesis in concerned with the development of a “socio-economic parameterization” to be coupled with a widely-used ESM, the Community Earth System Model (CESM). The module, dubbed POPEM (POpulation Parameterization for Earth Models), embeds the knowledge on system dynamics to model population, which is used to compute anthropogenic CO2 emissions at gridcell level. The model is coded as a FORTRAN routine to allow a better coupling with CESM.
The standalone version of POPEM is validated against historical records of population and emissions –UN population estimates and CDIAC emission estimates–. After such initial test, the module is coupled with CESM to generate present-climate climatologies. A 50-year simulation is run to evaluate the dynamical modeling of emissions. The outputs of the model are compared with a control simulation to evaluate the added value of POPEM.
The results illustrate that pointwise emissions lead to a better representation of precipitation, especially in the 30N-30S band. The improvements show not only in the annual mean, but also in the structure of precipitation and in the intra-annual cycle. Those outcomes suggest that it is advantageous to model CO2 emissions directly at model grid points rather than using the traditional, bulk, global forcing approach.
A bonus of the pointwise approach is that provides a flexible framework for testing alternative hypotheses. Thus, potential applications of POPEM include not only sensitivity analyses of local CO2 emissions policies, but also the added feature of performing simulations for ‘what-if’ scenarios.
By integrating POPEM in one of the state-of-art ESMs we set a step forward in the fully-coupling of Human and Natural components of the Earth system so ESMs simulations become a more precise and realistic depiction of the climate, also allowing a better investigation of the role of anthropogenic actions on climate change.
