DEFINE INTERESTING: OH GOD WE’RE ALL GOING TO DIE? WILL THE YEAR 2100 BE MORE LIKE THE MID-CRETACEOUS OR MID-PLIOCENE GLOBAL WARMING AND WHY IT MATTERS?

The warmer climates of the mid-Cretaceous and mid-Pliocene are separated by 100 million years, yet both may have more in common with the year 2100 than the climate of the year 2100 has in common with that of the pre-industrial. The Cretaceous and Pliocene have proved popular comparators of a warmer future Earth, and have been targets for climate modelers since the early days of computer models. Each has had a dedicated scientific community contributing hundreds to thousands of studies, providing data on paleogeography, life, and greenhouse gas levels – exactly the details required to design computer simulations. There have also been an equal volume of data studies providing interpretations of those past climates. These interpretations can be used to evaluate global climate models under the more extreme conditions that relate to our future, and iterating between data and modeling research tends to improve our understanding of paleoclimate as well that of the potential futures we would prefer to avoid.

Recent results from NASA’s global climate modeling research programs provide some context as to how warm paleoclimates compare to our near future. Pliocene simulations have been conducted as part of the IPCC PlioMIP-2 project, and Cretaceous simulations are in support of NASA’s NExSS Exoplanets research. While there are many simulations, sporting multiple combinations of forcings, the most “likely” combinations (as informed by geologic and paleontologic data) yield a mid-Cretaceous that was 7° C to 15° C warmer than our pre-industrial climate, and a mid-Pliocene that was 1° C to 2.5°C warmer. Compare to the range of temperatures produced by the NASA GCMs for two more extreme future forcing pathways (RCP6.0 and RCP8.5), where temperatures increase between 2.5° C and 6.5° C, even without incorporating many of the slower feedbacks that are in play at geologic time scales. In these simple terms, the future climate that our great-grandchildren may experience could be defined as interesting indeed, if you define interesting as more like that experienced by dinosaurs. Are we all going to die, like the dinosaurs? No, of course not (well, I might). In fact, dinosaurs and much life thrived quite handsomely in a warmer Cretaceous. But, our way of life can die, or at least be altered beyond our ability to sugar (or brown) coat that fact that we lacked the will to provide a better future for our descendants. This presentation will provide results from the latest climate simulations from two of NASA’s long-running deep-time paleoclimate modeling projects.