The workshop hosted by the committee provided a wealth of information concerning the existing scientific status of deep-time climate research, as well as a very broad range of topics that the community suggested as research foci for an improved understanding of Earth system processes during the transition to a warmer world. The committee assessed these topics and their potential to transform scientific understanding, and identified the following six elements of a deep-time research agenda as having the highest priority to address enduring scientific issues and produce exciting and critically important results over the next decade or longer.
Improved Understanding of Climate Sensitivity and CO2-Climate Coupling
Existing data indicate that climate forcing resulting from increased CO2 will, by the end of this century, rival that experienced during past greenhouse periods prior to the onset of the current glacial state. The paleoclimate record, which captures the climate response to a full range of levels of radiative forcing, can uniquely contribute to a better understanding of how climate feedbacks—both long and short term—and the amplification of climate change have varied with changes in atmospheric CO2 and other greenhouse gases. In the context of the large uncertainty in estimates of climate sensitivity described in Chapters 1 and 2, a high research priority for deep-time paleoclimatology is the determination of equilibrium climate sensitivity on multiple timescales, particularly during periods of greenhouse gas forcing comparable to that anticipated within and beyond this century if emissions are not reduced. Existing records of past warm periods already indicate climate sensitivity well above the estimated short-term range and show that the future temperature increase will most likely be amplified once the longer-term feedbacks that have not operated on human timescales (decades to centuries) during Earth’s current icehouse become relevant under warmer conditions.
Further mining of the deep-time geological archive will require focused efforts to improve the accuracy and precision of existing proxies for past atmospheric pCO2 and surface air and ocean temperatures, and to develop new proxies for other paleo-greenhouse and non-greenhouse gases and aerosols. Data using new and existing proxies could then be synthesized to develop an authoritative global temperature and atmospheric pCO2 history—at various resolutions—for the full span of Earth’s history. Improved constraints on levels of radiative forcing and equilibrium climate sensitivity are needed for past warm periods and major climate transitions. In addition, further study of intervals of possible CO2-climate decoupling