Biogeochemistry, Ecosystems and Climate Group Five Year Plan
The main conclusions of the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4) from Working Group 1 (WG1) were:
- the warming of the planet is unequivocal
- it is very likely that the global temperature increase observed over the past 100 years is due to human activities
- climate change this century is likely to be larger than in the 20th century
These conclusions could not have been reached without the use of climate models. Over the past several decades, these models have progressively become more refined and sophisticated. Current generation climate models (Atmosphere-Ocean General Circulation Models - AOGCMs) include atmosphere, land, sea ice and ocean components – the main parts of the physical climate system. These models are typically forced with estimates of past and future changes in greenhouse gases (GHG) concentrations.
It has been long recognized that both land and ocean biology can impact the concentration of CO2 in the atmosphere by taking up and releasing CO2. According to the current estimates, the earth’s biosphere is taking up about 50% of the human emissions of CO2. A very important question is whether or not this biological uptake will change in the future. In order to simulate the interactions of biology and climate, earth system models (ESMs) had to be developed.
To convert an AOGCM into an ESM, one needs to add components which can simulate the biogeochemical processes on the land and in the ocean. The modeling of these processes is a very new field of endeavor and, as a result, the level of uncertainty is quite high. It is unclear what parts of the system need to be included in the model and what parts can be neglected or greatly simplified, and what parts are prone to bias due to the biases in the underlying AOGCM. In many cases, there are only limited observations of key variables needed to evaluate model performance and to improve the models. A combination of modeling, theory and observations are needed to make progress in earth system modeling. Fortunately in recent years, progress is being made in all three areas.
This gives an overview of our plans to study the biosphere-climate interactions, starting with a description of our current models and their development. We then present our research and model development goals for the next several years. In the last section, we give a description of how we see ourselves serving the needs of both the scientific community and society.
II. Current Models
To start building the Earth System Model (ESM), we used as a base a successful climate model developed at GFDL, CM2.1. This model has been used in many climate studies including the most recent Intergovernmental Panel on Climate Change (IPCC) assessment, AR4. To this model, we added the ocean biogeochemistry component (TOPAZ) and replaced the land surface component with a new land dynamics model (LM3V), which simulates vegetation dynamics and land surface exchanges of energy, water and CO2 . This new model is called ESM2.1.
We are using this model in several climate studies. We have run an 1860 control integration. A control integration is an experiment where the radiative forcing – Greenhouse gases, aerosols, solar, volcanoes, land use, etc. - are all held constant. We also performed simulations of the observed changes over the 20th century and the future changes. We have just begun the analysis of these integrations and are preparing papers describing results of these studies.
We are currently in the process of improving ESM2.1 and are building two new ESMs – ESM2M and ESM2G. These two new models use an improved land dynamics model LM3, with improved hydrology, snow and soil thermodynamics coupled to the new vegetation component from LM3V. The first model, ESM2M, uses a new version of the ocean component model (MOM4). The second model, ESM2G, uses a different oceanic component, GOLD, with density-based vertical coordinate. We plan to use these models to study climate including the next IPCC (AR5) effort.
It is important to note that components beyond traditional climate foci are included in the new ESMs such as land use changes and the occurrence of wild fires. The need to characterize the ecological and biogeochemical processes requires that climate scientists at GFDL reach out to experts in many areas. Our first collaborations have been with Princeton University and the University of New Hampshire.
III. Model development and research goals over next few years
We plan to use our ESMs to study past, present and future climates and biosphere dynamics. As noted above, we plan to use ESM2M and ESM2G as part of GFDL’s contribution to the IPCC AR5. We will also seek to understand past observed climate and carbon changes. It is likely that these studies will expose aspects of our models that need to be improved. In addition to studying past climate changes, we will make projections of future climates. As part of this activity, we will investigate the causes of uncertainty in our simulations. We are also investigating the degree to which our models can be applied to assess ecological impacts.
The model improvement and development will continue to be an important component of our research. We are already working on incorporating additional biogeochemical cycles such as nitrogen into the ESMs. Nitrogen plays a crucial role in determining plant growth rates and coastal ecosystem behavior. Adding these new biogeochemical cycles will allow us to study new and different facets of the impact of human activities on both the biosphere and on climate. We are also working on improving the capability of these models to simulate the potential climate and anthropogenic impacts (e.g. ocean acidification and hypoxia, terrestrial air pollution) on ecosystems through improved representation of biodiversity and physiological and ecological functioning.
Using ESM2M and ESM2G will also allow us to investigate the role of the ocean in both carbon and heat uptake in the transient climate change problem. Uncertainties in ocean heat uptake have long been known to be important for understanding the differences among models for future projections of climate changes. By using two different ocean component formulations, we will be able to improve our understanding of underlying cause and consequences of these uncertainties.In addition, studies of the distant past climates such as the Last Glacial Maximum (LGM – about 21,000 years ago) will be conducted. Drawing on the experience of the LGM study with CM2.1, we will use ESM2.1 to explore biosphere-climate interactions and their implications for both physical climate and the carbon cycle at that period. These activities are essential steps in building confidence in our model projections of future climate changes and they highlight various model strengths and weaknesses that need to be addressed.
IV. Community service
We anticipate our models to play an important role in the IPCC AR5. An important part of this service is making the model results available to the AR5 authors and the broader climate community. We plan to make the model data available via the data portal hosted and managed by GFDL. In addition to providing GFDL model data, this portal will also allow users to obtain any of the Coupled Model Intercomparison Project version 5 (CMIP5) data sets via a network of data servers managed by DOE’s Program for Climate Model Diagnosis and Intercomparison (PCMDI) through the Earth System Grid (ESG).
We will also communicate our findings through papers published in the refereed literature. This literature will be assessed by the AR5 authors and incorporated into the IPCC findings. In addition, we will communicate our results at various scientific seminars, workshops and by serving on national and international committees. GFDL scientists will also participate in national and international assessments.