Model-record experiments will be particularly important for developing predictions in data-sparse regions, as the basis for hypotheses that can be tested by the collection of new data. Because climate models simulate spatial and temporal patterns on a regular grid and at regular time intervals, they can provide a context for integrating or synthesizing environmental and fossil records that are discontinuous in space and time, or are otherwise incomplete.
The large-scale record of climate change over the past 8 Ma is reasonably well known, although much remains to be understood about the interactions and feedbacks among the various climate forcing factors. At issue are the relative influences on African and Eurasian climate from orbital monsoonal forcing, high-latitude ice volume changes, atmospheric carbon dioxide (CO2) changes, Tibetan and East African uplift, and sea-level or ocean gateway changes, all of which changed over this time period. With improved density, accuracy, and dating of environmental records, there is an opportunity to use climate models to ask more detailed questions and to obtain more detailed information about the climate, water resources, and vegetation comprising hominin habitats. In particular, the availability of accurate estimates of atmospheric CO2 will permit simulation of both the direct effects of greenhouse gases on climate, as well as the possible physiological effects on vegetation of changing levels of CO2. These models can only be accurately parameterized and their outputs tested by reference to actual paleoenvironmental data from the interior of Africa and its surrounding oceans. With the availability of greenhouse gas records and known orbitally caused changes in solar radiation, models have proven to be remarkably accurate in simulating past climates.
Implementing this research vision will require community and organizational flexibility as it embraces a more collaborative and cross-disciplinary model, involving a transformative shift in how paleoanthropological research is conducted. Although the exploration of human origins is inherently an international activity, large field-based research projects have been largely conducted and funded along national lines, and broader partnerships and funding efforts are still relatively rare. International collaboration and cooperation focused on understanding the extent to which the earth system was a factor in human evolution offers the potential for applying the intellectual, organizational, and funding resources of a much wider community to an important research problem.
We envision a new scientific program for international climate and human evolution studies that involves both essential and supporting components: