Dec 11 2018
The future of humans on Earth could also be their past.
In a research reported in the Proceedings of the National Academy of Sciences on Monday, December 10th, 2018, scientists reveal that humans are reversing an everlasting cooling trend tracing back at least 50 million years. And it has taken only two centuries.
It is expected that by 2030, Earth’s climate will resemble that of the mid-Pliocene, going back over three million years in geologic time. If reductions in greenhouse gas emissions are not achieved, by 2150, climates could be comparable to the warm and largely 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,” stated Kevin Burke, the study’s lead author, who conducted the study 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 that exist on Earth at present had an ancestor that survived the Eocene and the Pliocene; however, whether the flora and fauna and the humans we are familiar with can adapt to such rapid changes is yet to be seen. The rapid rate of change seems to be faster than anything experienced by life on the planet earlier.
The new research is based on the study of Williams and colleagues first published in 2007, which compared future climate projections to historical climate data from the early 20th century. The new research relies on extensive data related to climate conditions to perform in-depth investigations of 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. 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.
John “Jack” Williams, Paleoecologist, Professor of Geography, University of Wisconsin-Madison.
At the time of the Eocene, the continents of Earth were packed more closely together and global temperatures averaged 23.4 °F (13 °C) warmer than existing temperatures. Dinosaurs had recently become extinct and the first mammals, such as ancestral horses and whales, were spreading worldwide. Swampy forests such as those found today in the southern United States occupied the Arctic.
In the Pliocene, North and South America united tectonically, land bridges enabled animals to spread over continents, the climate was arid, and the Himalayas formed. Temperatures ranged between 3.2 °F and 6.5 °F (1.8–3.6 °C) warmer than existing temperatures.
For the research, Burke and Williams—together with collaborators at the University of Bristol, Columbia University, University of Leeds, NASA Goddard Institute for Space Studies, and the National Center for Atmospheric Research—investigated the similarities between future climate projections as set forth by the Intergovernmental Panel on Climate Change Fifth Assessment Report and various periods of geologic history.
These included the Early Eocene, the mid-Pliocene, the Last Interglacial (129,000 to 116,000 years ago), the mid-Holocene (6000 years ago), the pre-industrial era (before AD 1850), and the early 20th century.
The researchers used Representative Concentration Pathway 8.5 (RCP8.5), which represents a future climate scenario in which greenhouse gas emissions are not mitigated, RCP4.5, a scenario in which greenhouse gas emissions are moderately reduced, and climate simulations using three distinct yet well-established models: the Hadley Centre Coupled Model version 3, the Goddard Institute for Space Studies ModelE2-R, and the Community Climate System Model.
Although each of these models has its own flaws, each one represents the best available data and sophisticated techniques.
In both scenarios and across each model, when compared to earlier eras, the climate of Earth most closely resembled the mid-Pliocene by 2030 (under RCP8.5) or 2040 (under RCP4.5). In the RCP4.5greenhouse gas stabilization scenario, the climate stabilizes at mid-Pliocene-like conditions; however, under the RCP8.5 higher greenhouse gas emissions scenario, the climate continues to warm until it starts resembling the Eocene in 2100, accomplishing Eocene-like conditions more broadly by 2150.
The models demonstrated the deep-geological climates to emerge first from the center of continents and then expanding outward as time passed. There is an increase in temperatures and precipitation, ice caps melt, and climates turn out to be temperate close to the Earth’s poles.
Madison (Wisconsin) warms up more than Seattle (Washington) does, even though they’re at the same latitude. 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.
John “Jack” Williams, Paleoecologist, Professor of Geography, University of Wisconsin-Madison.
The research also demonstrated that under RCP8.5, “novel” climates appear across about 9% of the planet. These conditions do not have notable historical or geologic precedent and they concentrate in northern Australia, eastern and southeastern Asia, 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. 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.
Kevin Burke, Study Lead Author, University of Wisconsin-Madison.
Nearly a decade earlier, Johan Rockström, a Swedish scientist, and his coworkers introduced the concept of “safe operating space,” making reference to the climate conditions under which modern agricultural societies developed. According to Williams and Burke, through comparison to the deep past, better insights can be achieved into 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. 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.
John “Jack” Williams, Paleoecologist, Professor of Geography, University of Wisconsin-Madison.
In their study, the researchers make attempts to strike a balance between alarm and optimism. For one thing, Earth is heading toward the unknown in our children’s and grandchildren’s lifetimes. For another, for a long time, life has proven to be resilient. Moreover, according to Williams, who is a faculty affiliate with the UW-Madison Nelson Institute Center for Climatic Research, in various places, humans are turning their back towards fossil fuels and opting for more sustainable and carbon-free energy sources. However, there is still more 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,” stated 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.”
The National Science Foundation (DEB-1353896) and the Wisconsin Alumni Research Foundation funded the research.