Paleogeograpy in the middle of the Paleogene Period. Graphic: Wikipedia

By Eric Holthaus
11 December 2018
(Grist) – Our current rate of warming will quickly lead us back to a climate that predates the evolution of modern humans, according to a new study in the Proceedings of the National Academy of Sciences. That kind of rapid change has no direct comparison in all of Earth’s multi-billion year history.“The only thing that comes to mind is a meteorite impact,” says co-author Jack Williams, a paleoecologist at the University of Wisconsin-Madison.The researchers analyzed the current, near-past, and near-future climates for every part of the planet, and then compared them to what likely existed during similar warming periods of the distant past. The results were shocking, even to Williams.“We are creating a geological-scale climate event,” Williams says. “These things don’t happen that often, and we don’t know how humans will do through it.”Without rapidly reducing emissions, we’ll quickly go back to a climate similar to somewhere between the Pliocene and Eocene — geological epochs that occurred about 3 million, and about 56 million years ago, respectively. Both would have hellish consequences and likely reshape human civilization permanently.During the Pliocene period, global temperatures were about 2-4 degrees Celsius warmer than today and sea levels eventually stabilized about 60 feet higher than current levels. It was a world largely inconsistent with natural ice formation.By 2030, under a business-as-usual scenario, Pliocene-like conditions become the closest match for most land areas, according to the study. Under a moderate climate action scenario, like the lax pledges of the Paris Agreement, that could be extended out to 2040. Only a drastic, economy-wide makeover within the next decade, consistent with limiting warming to 1.5 degrees C, would avoid the transition.“This is coming up pretty fast,” Williams says.An even more worrying period in Earth history was the Eocene, about 56 million years ago. The warmest part of this period — the Paleocene-Eocene Thermal Maximum — lasted around 200,000 years and was one of the warmest times in Earth history. The 8 degrees C-warmed world triggered a deep-sea mass extinction event and rainstorms so intense they scoured away the land surface at a continent scale. Humans are currently releasing carbon into the atmosphere at approximately 50 times the rate of the volcanic eruptions that led to the Eocene warm period. [more]

Welcome to the Eocene, where ice sheets turn into swamps

12 December 2018 (University of Leeds) – A recently published paper shows that humans are reversing a long-term cooling trend, which traces back at least 50 million years. And it’s taken just two centuries.The paper, co-authored by Professor Alan Haywood from the School of Earth and Environment, was published in the Proceedings of the National Academy of Sciences and was led by researchers from the University of Wisconsin-Madison.The study examined the future climate projections, set by the Intergovernmental Panel on Climate Change Fifth Assessment Report and the similarities these have with several periods of geologic history. The findings suggest that the Earth’s climate is expected to resemble the much higher temperatures of the Pliocene period of three million years ago by 2030. And without reduction of greenhouse gases, by 2050, the climate could resemble the warmth of the ice-free Eocene period (50 million years ago). “After studying the Pliocene for the last 20 years in order to find out more about how warm climates work, it is sobering to know that, all things being equal, I will live long enough to see and recognise more and more characteristics of a climate state which has not existed for more than 3 million years” said Professor Alan Haywood.Lead author, Professor John Williams and colleagues first published work on this topic in 2007 which focused on the climate data from the early 20th century. Whereas this study examines climate conditions using more extensive data, enabling a deeper understanding of the Earth’s geological past and better comparisons.Recent findings have shown that the accelerated rate of change appears to be faster than anything life on the planet has experienced before. Whether or not humans and the flora and fauna we understand today can adapt to these rapid changes is still an uncertainty.Professor Williams said: “We can use the past as a yardstick to understand the future, which is so different from anything we have experienced in our lifetimes. People have a hard time projecting what the world will be like five or 10 years from now. This is a tool for predicting that — how we head down those paths, and using deep geologic analogs from Earth’s history to think about changes in time. We’ve seen big things happen in Earth’s history — new species evolved, life persists and species survive. But many species will be lost, and we live on this planet. These are things to be concerned about, so this work points us to how we can use our history and Earth’s history to understand changes today and how we can best adapt.”

Climate change could take us back 50 million years

ABSTRACT: As the world warms due to rising greenhouse gas concentrations, the Earth system moves toward climate states without societal precedent, challenging adaptation. Past Earth system states offer possible model systems for the warming world of the coming decades. These include the climate states of the Early Eocene (ca. 50 Ma), the Mid-Pliocene (3.3–3.0 Ma), the Last Interglacial (129–116 ka), the Mid-Holocene (6 ka), preindustrial (ca. 1850 CE), and the 20th century. Here, we quantitatively assess the similarity of future projected climate states to these six geohistorical benchmarks using simulations from the Hadley Centre Coupled Model Version 3 (HadCM3), the Goddard Institute for Space Studies Model E2-R (GISS), and the Community Climate System Model, Versions 3 and 4 (CCSM) Earth system models. Under the Representative Concentration Pathway 8.5 (RCP8.5) emission scenario, by 2030 CE, future climates most closely resemble Mid-Pliocene climates, and by 2150 CE, they most closely resemble Eocene climates. Under RCP4.5, climate stabilizes at Pliocene-like conditions by 2040 CE. Pliocene-like and Eocene-like climates emerge first in continental interiors and then expand outward. Geologically novel climates are uncommon in RCP4.5 (<1%) but reach 8.7% of the globe under RCP8.5, characterized by high temperatures and precipitation. Hence, RCP4.5 is roughly equivalent to stabilizing at Pliocene-like climates, while unmitigated emission trajectories, such as RCP8.5, are similar to reversing millions of years of long-term cooling on the scale of a few human generations. Both the emergence of geologically novel climates and the rapid reversion to Eocene-like climates may be outside the range of evolutionary adaptive capacity.SIGNIFICANCE: The expected departure of future climates from those experienced in human history challenges efforts to adapt. Possible analogs to climates from deep in Earth’s geological past have been suggested but not formally assessed. We compare climates of the coming decades with climates drawn from six geological and historical periods spanning the past 50 My. Our study suggests that climates like those of the Pliocene will prevail as soon as 2030 CE and persist under climate stabilization scenarios. Unmitigated scenarios of greenhouse gas emissions produce climates like those of the Eocene, which suggests that we are effectively rewinding the climate clock by approximately 50 My, reversing a multimillion year cooling trend in less than two centuries.

Pliocene and Eocene provide best analogs for near-future climates