The Climate of the Pliocene: Simulating Earth's Last Great Warm Period
Much of the research conducted by scientists at the Goddard Institute for Space Studies is aimed at developing tools for simulating future climate change. The ultimate objective is to help anticipate the impact that those changes will have on society and the environment. The development of computer models is central to our efforts, and global climate models (GCMs), in particular, are the primary tool we use to simulate the Earth's environment and the forces that affect it. Among those forces are many which are anthropogenic, or human-caused, including increased greenhouse gases and aerosols, ozone depletion, and deforestation.
In employing climate models, we must make every attempt possible to verify that they are capable of accurately portraying Earth's climate and its sensitivity to change. Validating a GCM's equilibrium capability is done by comparing simulations of the modern climate, often referred to as current climate control simulations, to observations. However, despite our interest in anthropogenic influences on future climate, testing the GCM's sensitivity to change generally relies on our ability to understand natural climate changes from the past. Predictions of future changes gain credibility when our models can accurately simulate changes that have actually occurred. Unfortunately, historical records of most climatological variables, such as temperature and precipitation, rarely exceed 100 years in length. Moreover, many of the changes anticipated in the future are likely to exceed historical precedents. Thus, we commonly step back further in time and examine the geologic record, which contains examples of global-scale climate change similar in magnitude to that predicted to occur during the 21st century.
Many past time periods have been simulated, both for the purpose of evaluating model capabilities and as a technique for studying the Earth's climatic evolution. Simulations of key periods during the last ice age commonly provide excellent climate change scenarios of large magnitude. If our interest, however, is in climates warmer than today, we must look back at least three million years, to the middle of the Pliocene epoch, to find a period in Earth history with global average temperatures more than a degree (Celsius) higher than the present.