sense the scientific community must strive to make the presentation of deep-time paleoclimate information as understandable as possible.

The paleoclimate record contains facts that are surprising to most people. For example, there have been times when the poles were forested rather than being icebound; there were times when the polar seas were warm; and there were times when tropical forests grew at midlatitudes. For the majority of Earth’s history, the planet has been in a greenhouse state rather than in the current icehouse state. Such concepts provide an opportunity to help disparate audiences understand that the Earth has archived its climate history and that this archive, while not fully understood, provides crucial lessons to improving our understanding of Earth’s climate future.

The possibility that our world is moving toward a “greenhouse” future continues to increase as anthropogenic carbon builds up in the atmosphere, providing a powerful motivation for understanding the dynamics of Earth’s past “greenhouse” climates that are recorded in the deep-time geological record. It is the deep-time climate record that has revealed feedbacks in the climate system that are unique to warmer worlds—and thus are not archived in more recent paleoclimate records—and that might be expected to become increasingly relevant with continued warming. It is the deep-time record that has revealed the thresholds and tipping points in the climate system that have led to past abrupt climate change, including amplified warming, substantial changes in continental hydroclimate, catastrophic ice sheet collapse, and greatly accelerated sea level rise. Further, it is uniquely the deep-time record that has archived the full temporal range of climate change impacts on marine and terrestrial ecosystems, including ecological tipping points. An integrated research program—a deep-time climate research agenda—to provide a considerably improved understanding of the processes and characteristics over the full range of Earth’s potential climate states offers great promise for informing individuals, communities, and public policy.

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