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Our future on Earth may also be our past. In a study published in the Proceedings of the National Academy of Sciences, researchers show that humans are reversing a long-term cooling trend tracing back at least 50 million years. And it's taken just two centuries.

Epihippus gracilis, one of the many early horses found in the Hancock Mammal Quarry in Oregon, depicted around 30 million years ago. Their ancestors would have gotten their start in the Eocene [Credit: National Park Services]

By 2030, Earth's climate is expected to resemble that of the mid-Pliocene, going back more than 3 million years in geologic time. Without reductions in our greenhouse gas emissions, our climates by 2150 could compare to the warm and mostly ice-free Eocene, an epoch that characterized the globe 50 million years ago.

"If we think about the future in terms of the past, where we are going is uncharted territory for human society," says the study's lead author, Kevin Burke, who conducted the work while a graduate student in the lab of paleoecologist John "Jack" Williams, professor of geography at the University of Wisconsin-Madison. "We are moving toward very dramatic changes over an extremely rapid time frame, reversing a planetary cooling trend in a matter of centuries."

All of the species on Earth today had an ancestor that survived the Eocene and the Pliocene, but whether humans and the flora and fauna we are familiar with can adapt to these rapid changes remains to be seen. The accelerated rate of change appears to be faster than anything life on the planet has experienced before.

The new study builds upon work Williams and colleagues first published in 2007, which compared future climate projections to historical climate data from the early 20th century. The new study relies on extensive data about climate conditions to probe much deeper in Earth's geologic past and expand those comparisons.

"We can use the past as a yardstick to understand the future, which is so different from anything we have experienced in our lifetimes," says Williams. "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."

During the Eocene, Earth's continents were packed more closely together and global temperatures averaged 23.4 degrees Fahrenheit (13 degrees Celsius) warmer than they are today. Dinosaurs had recently gone extinct and the first mammals, like ancestral whales and horses, were spreading across the globe. The Arctic was occupied by swampy forests like those found today in the southern U.S.

Future climate analogs for the years 2020, 2050, 2100 and 2200 according to three well-established models. If greenhouse gas emissions are not curbed, the study says, the climate will continue to warm until it begins to resemble the Eocene in 2100 [Credit: Burke et al. 2018]

In the Pliocene, North and South America joined tectonically, the climate was arid, land bridges allowed animals to spread across continents and the Himalayas formed. Temperatures were between 3.2 and 6.5 degrees Fahrenheit (1.8 to 3.6 degrees Celsius) warmer than they are today.

For the study, Burke and Williams -- along with colleagues at the University of Bristol, Columbia University, University of Leeds, NASA Goddard Institute for Space Studies and the National Center for Atmospheric Research -- examined the similarities between future climate projections as set forth by the Intergovernmental Panel on Climate Change Fifth Assessment Report and several periods of geologic history.

These included the Early Eocene, the mid-Pliocene, the Last Interglacial (129 to 116 thousand years ago), the mid-Holocene (6,000 years ago), the pre-industrial era (before A.D. 1850) and the early 20th century.

They used Representative Concentration Pathway 8.5 (RCP8.5), which represents a future climate scenario in which we do not mitigate greenhouse gas emissions, and RCP4.5, a scenario in which we moderately reduce greenhouse gas emissions, and climate simulations using three different but well-established models: the Hadley Centre Coupled Model version 3, the Goddard Institute for Space Studies ModelE2-R and the Community Climate System Model.

While not without their flaws, each of these models represents the best available data and state-of-the-art techniques.

Under both scenarios and across each model, compared to previous eras, the Earth's climate most closely resembled the mid-Pliocene by 2030 (under RCP8.5) or 2040 (under RCP4.5). Under the greenhouse gas stabilization scenario of RCP4.5, the climate then stabilizes at mid-Pliocene-like conditions, but under the higher greenhouse gas emissions of RCP8.5, the climate continues to warm until it begins to resemble the Eocene in 2100, achieving Eocene-like conditions more broadly by 2150.

The models showed these deep-geological climates emerging first from the center of continents and then expanding outward over time. Temperatures rise, precipitation increases, ice caps melt and climates become temperate near the Earth's poles.

"Madison (Wisconsin) warms up more than Seattle (Washington) does, even though they're at the same latitude," Williams explains. "When you read that the world is expected to warm by 3 degrees Celsius this century, in Madison we should expect to roughly double the global average."


The study also showed that under RCP8.5, "novel" climates emerge across nearly 9 percent of the planet. These are conditions that do not have known geologic or historical precedent and they concentrate in eastern and southeastern Asia, northern Australia and the coastal Americas.

"Based on observational data, we are tracking on the high end of the emissions scenarios, but it's too soon to tell," says Burke. "We may be somewhere between RCP4.5 and RCP8.5, though if we increase our climate mitigation efforts -- like switching to renewable energy -- we could find ourselves closer to the low end."

About a decade ago, Swedish scientist Johan Rockström and colleagues introduced the idea of "safe operating space," referring to the climate conditions under which modern agricultural societies developed. By comparing to the deep past, Williams and Burke say, we are able to better understand the planetary boundaries and thresholds that delineate this space.

"The further we move from the Holocene, the greater the potential that we move out of safe operating space," says Williams, a faculty affiliate with the UW-Madison Nelson Institute Center for Climatic Research. "In the roughly 20 to 25 years I have been working in the field, we have gone from expecting climate change to happen, to detecting the effects, and now, we are seeing that it's causing harm. People are dying, property is being damaged, we're seeing intensified fires and intensified storms that can be attributed to climate change. There is more energy in the climate system, leading to more intense events."

In their paper, the researchers try to strike a balance between alarm and optimism. On the one hand, Earth is headed into the unknown in our children's and grandchildren's lifetimes. On the other, life has long proven to be resilient. And, Williams says, in many places we are moving away from fossil fuels toward more sustainable and carbon-free energy sources. But more needs to be done.

"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," says Williams. "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."

Author: Kelly April Tyrrell | Source: University of Wisconsin-Madison [December 10, 2018]

New research by an international team raises questions about the timing and nature of early interactions between indigenous people and Europeans in North America.

A human face effigy from ceramic vessel from the Mantle site [Credit: Archaeological Services Inc./Andrea Carnevale]

The European side of first contact with indigenous people and settlement in northeast North America is well known from European sources. Until now it's been assumed that the finds of dated European artifacts provide a timeline for the indigenous peoples and settlements of this period as well. New research suggests this may be a mistake in cases where there was not direct and intensive exchange.

Radiocarbon dating and tree-ring evidence shows that three major indigenous sites in Ontario, Canada, conventionally dated 1450-1550 are in fact 50-100 years more recent. This dates the sites to the worst period of the Little Ice Age, around 1600.

"This seems extraordinary: Given this was only 400 years ago, how can we have been wrong by as much as 25 percent?" said first author Sturt Manning, the Goldwin Smith Professor of Classical Archaeology, chair of the Department of Classics and director of the Cornell Tree-Ring Laboratory.

Manning is lead author of "Radiocarbon Re-dating of Contact-era Iroquoian History in Northeastern North America," published in Science Advances. Other Cornell authors include Cornell Tree-Ring Laboratory senior researcher Carol Griggs '77, Ph.D. '06, and doctoral student Samantha Sanft. The paper represents the first major findings of the "Dating Iroquoia" project, a National Science Foundation-funded effort led by Manning and co-director Jennifer Birch (University of Georgia).

Previously, dates in the early contact period were based on the absence – and then presence – of types of glass beads and other European trade goods in excavated sites, along with shifts in material culture, such as changes in ceramic designs. Dates were assigned according to "time transgression," the assumption that when European goods are found in one place with a confirmed date associated with them, that same date can be used for other places where those trade goods are found.

"But goods don't get distributed evenly within societies or across distances," said Manning. "This is a vast area with complex local societies and economies, so the concept that everybody gets the same thing necessarily all at once is a bit ludicrous in retrospect."

The team's chronological findings dramatically rewrite how history has been understood in the region. The period of first European contact, rather than following major changes in Iroquoian society, can now be seen to coincide with those changes. According to Birch, an expert on Iroquoian societies, "Our work has shown that, at least for some communities, contact-era transformations happened much later and much more rapidly than previously assumed."

"Of course, we've dated only one site sequence, and there are many more," Manning said. "What this paper really shows is we now need to reassess all those site sequences where there's not a clear historical link or association."

The researchers first examined the Warminster site in Canada, believed to be visited by French explorer Samuel de Champlain in 1615. Using radiocarbon isotope and dendrochronological (tree ring) dating, combined with a mathematical technique, determined the indigenous settlement at the location to date from between 1585 and 1624, which corresponded with Champlain's visit. Archaeological evidence and provided confirmation of the accuracy of their techniques.

The team then assessed a series of well-known, high profile settlements, Draper-Spang-Mantle. In the 16th century, Iroquoian societies lived in village communities for approximately 10 to 50 years; once the local resources were exhausted, the community relocated the village. Archaeological evidence indicates that these three villages were occupied in sequence by the same ancestral Huron-Wendat community. Mantle, the latest site in the sequence, was shown to date to between 1599 and 1614, partly contemporaneously with Warminster.

Author: Linda B. Glaser | Source: Cornell University [December 05, 2018]

A new study shows extreme heat events both in the summer and in the winter are increasing across the U.S. and Canada, while extreme cold events in summer and winter are declining.

Soybeans show the effect of the Texas drought near Navasota, TX on Aug. 21, 2013 [Credit: USDA]

A new study in the in Journal of Geophysical Research: Atmospheres, a publication of the American Geophysical Union, examined absolute extreme temperatures--high temperatures in summer and low temperatures in winter--but also looked at relative extreme temperature events--unusually cold temperatures and unusually warm temperatures throughout the year.

The new study found both relative and absolute extreme heat events have increased across the US and Canada since 1980. This upward trend is greatest across the southern US, especially in the Ozarks and southern Arizona, as well as northern Quebec. That means there are more extremely hot days during the summer as well as more days that are considered extremely hot for the time of year, like abnormally warm days in the winter.

The new research also found both relative and absolute extreme cold events are decreasing, most notably in Alaska and Northern Canada, along with patches along the US Atlantic coast. In these areas, there are fewer instances of temperatures that are extremely cold either compared to the normal range, like in winter, or for the time of year, like unusually cold days in the summer.

Global mean surface temperature, the most frequently cited indicator of climate change, has been steadily increasing since the 1970s. However, temperature extremes pose a greater ecological risk to many species than average warming, according to the study's authors.

The new study is one of the first to explore relative extreme temperature events, which are changing more rapidly than absolute temperature extremes, and can have important implications for the environment, agriculture and human health, according to Scott Sheridan, professor in the department of geography at Kent State University and lead author of the new study.

"Typically for this kind of research we look at the highest temperatures in the summer and lowest temperatures in the winter. But we've also seen that extreme temperatures that are really anomalous for the time of year can have a high impact--these relative extremes are important and underappreciated," he said.

Investigating temperature extremes

To investigate how extreme temperature events have been changing over time, Sheridan and his co-author conducted a climatology of cold and heat events, both absolute and relative, for North America, followed by an analysis of how they have changed from 1980-2016.

Trends in Extreme Heat Events (EHE), Extreme Cold Events (ECE), Relative Extreme Heat Events (REHE), and Relative Extreme Cold Events (RECE) in days per decade, 1980-2016. Dots indicate grid cells  in which the trend is statistically significant (p<.05) [Credit: Scott Sheridan]

Relative extreme temperature events are changing faster than absolute extreme events, and often occur outside of seasonal norms, according to the new study. In the eastern half of the US, relative extreme heat events occur as early as mid-winter into early spring. Out-of-season extreme temperatures can cause early thaws in mild winters or catch vulnerable populations unprepared and unacclimated.

Across parts of the Arctic, extreme cold events have become almost entirely nonexistent and increasingly difficult to identify, according to the researchers.

"Relative temperature anomalies can trigger what are called phenological mismatches, where a mismatch in the temperature and the season can cause trees to bloom too early and birds and insects to migrate before there is appropriate food," Sheridan said.

Most notable is the highly anomalous warm event in March 2012, which included persistent mid-summer warmth in multiple locations. The event produced a 'false spring' in which vegetation prematurely left dormancy, so that it was not prepared for subsequent frosts, leading to large agricultural losses in certain areas, according to the researchers.

There is some evidence that early-season heat events are more hazardous to humans than heat events later in the season. When people are not acclimatized to hotter temperatures, they are more vulnerable to negative health impacts, especially the elderly, infants, young children, and people with chronic health problems or disabilities, according to the researchers.

The study clearly underlines the importance of not just looking at high temperatures in the summer but also looking at relative temperatures, said Kristie Ebi, professor of Environmental and Occupational Health Sciences at the University of Washington, who was not involved in the study.

"Using information generated in the study on regional patterns in extreme weather events, particularly relative extremes in temperature, early warnings could be issued that include information on what people can do to protect themselves and to protect crops and ecosystems," Ebi said.

Source: American Geophysical Union [November 26, 2018]