A fourth priority is to formalize research funding to encourage scientific exchange and strategic analysis of climate-evolution hypotheses by earth scientists, paleoanthropologists, and faunal researchers. High-precision analyses of climate and paleoecology should be integrated with the efforts of climate modelers. This overall approach, in which projects are unified by shared strategic goals, requires unprecedented collaboration across disciplines and encourages the development of innovative scientific tools and data exchange.

THEME II: INTEGRATING CLIMATE MODELING, ENVIRONMENTAL RECORDS, AND BIOTIC RESPONSES

The integration of physical and biotic records of past environmental change with regional climate modeling studies offers considerable potential for an improved understanding of the causes of the changes, as a basis for exploring specific questions concerning potential connections between environmental changes and hominin evolution and dispersal. Experiments using climate models can help us understand why climate changed (e.g., did greenhouse gas concentrations decrease sufficiently so that winter snows persisted through summer and created the conditions for glacial growth?), what happened (where and by how much did ice sheets grow?), and how events in one region influenced environments elsewhere through global and regional changes in atmospheric and oceanic circulation. A corresponding set of questions can be formulated for orbital-forcing of insolation changes, for ocean gateway changes, or for combinations of these factors. Moreover, climate models simulate spatial and temporal patterns on a regular grid and at regular time intervals that can provide a context for integrating or synthesizing environmental and fossil records that are discontinuous in space and time, or are otherwise incomplete. They can also provide the basis for predictions in data-sparse regions, to provide hypotheses that can be tested by the collection of new data.

In some cases, it will be highly desirable to simulate the climate (or climate change) at small spatial scales. This might be the case, for example, in regions with large topographic variability (see Box 3.1) such as within the East African Rift Valley or the East African highlands. In such regions, large differences in climate (or climate change) are found on scales of several 10s or 100s of kilometers. At present, there are two main approaches to simulating the climate at such high spatial resolution. The most straightforward approach is to run a global climate model at very high resolution, thereby avoiding the problem of spurious effects from lateral boundary conditions that occur when using a regional or limited-area model. With adequate computer resources, using a global model of high spatial resolution is the preferred approach. In some cases, however, lateral boundary conditions from a global model of intermediate spatial resolution may be useful to force a limited-area model (e.g., for the region of East Equatorial Africa). In that case, an awareness of the problems of lateral boundary conditions



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