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Climate change recorded in the Earth's layers

Dr. Karen Grove held audience members of her recent library talk on the edge of our seats. In a truncated version of the course she will teach at Osher Lifelong Learning Institute (OLLI) at Southern Oregon University in the spring, she guided us through layer by layer of local sedimentary rock, explaining the geological history of the Rogue Valley. She mentioned her fall 2018 geology course: “Billions of Years of Climate Change on Earth.” My ears perked up; might Karen have recommendations for how we could apply knowledge of geological climate records into local action?

Trained as a geologist and oceanographer, first in her home state of Maryland, then in graduate school at Stanford, Karen spent her academic career educating students at San Francisco State University on how to interpret the layers of sediment around the Bay Area. She and her geologist husband retired to Ashland three and a half years ago; since then Karen has refocused her attention upon the historical record revealed by local geological formations.

When we met to discuss climate change, Karen explained that geologists determine planetary warmth by analyzing the isotopes of oxygen atoms found in the microscopic shells of ancient sea creatures (the material from which limestone forms). Lighter oxygen isotopes are captured in frozen ice-caps during colder climatic periods, while heavier isotopes remain in sea water; as the Earth warms and ice-caps melt, not only do lighter isotopes return to the ocean, but these changes are reflected in sedimentary layers deposited as waters intrude inland.

By interpreting the mineral components of sedimentary layers, geologists have come to understand that during the past 2.5 million years our planet’s temperature has fluctuated over 100,000-year cycles, varying between chilly glacial periods and warmer inter-glacial phases.

Several dynamics factor into the causes of Earth climate variation — among them volcanic activity, asteroid strikes and tectonic repositioning of the continents. And, mostly over the last 2.5 million years, fluctuating temperature cycles have resulted from the Earth’s elliptically-shaped orbit around the Sun, causing solar radiation to hit the plant in differing spots.

The Earth has been in a warming phase over the past 18,000 years. As recorded in Earth’s uppermost layers, incremental increases in temperature have led to shifts in the floristic range of key edible plants, as well as the animals (and humans) feeding upon them. During this warm period (roughly 12-14,000 years ago) First People arrived here in Oregon, as well as along the California coast. In order to address climatic fluctuations, West Coast peoples practiced a lifestyle that accommodated seasonal (or longer) migration, living in bio-degradable bark housing that could easily be replaced. By contrast, people in Eurasia (and other locations) responded to the last 10,000 year’s comfortable temperatures by settling into “sedentary agricultural” societies — growing crops and living in semi-permanent housing made of stone or brick.

Though better in tune with the environment, a migratory lifestyle was physically stressful, often leaving individuals at the mercy of the elements. Sedentary agriculture had its own set of drawbacks, but taking control of the immediate environment facilitated population growth and development of new technologies. This mode of social organization spread across Eurasia and, in time, was exported world-wide as part of European colonialist expansion, ultimately leading to the industrial revolution, the unearthing of coal and petroleum, and an exponential rise in population.

In the past century, human’s behavioral choices have translated into clear numerical data. As Karen pointed out, that Earth’s current “warm” phase should have peaked out and global temperatures begun to decline. To the contrary, the planet’s temperature has increased by an additional one degree Celsius over just the last 100 years, while atmospheric carbon dioxide has risen to levels not seen for 2 million years.

These facts belie claims made by climate change deniers that current warming trends are part of a natural process. Karen stated: “My goal is to have people better understand how climate changes naturally, so that they can understand that our current warming is the opposite of the natural cycles, and is caused by human actions.”

Karen’s recommendation for one action that readers might take is for them to engage with science-based organizations that can lobby the powers-that-be into setting rational climate change policies.

“One organization you might support that is really focused upon science, and works to influence the opinion of policy-makers,” she said, “is the Union of Concerned Scientists (UCS). It is, in my opinion, the best group doing this type of work, with the intention of making this a safer world for life.”

UCS has an extensive website at bit.ly/2QE2vKK that includes material on what one can do in the face of climate change. There are also educational videos on its YouTube channel at bit.ly/2QLqEiN.

Karen will be offering a six-week course on sedimentary geology at OLLI in the spring, and may teach her Climate Change course again next fall. She may also offer a talk on climate change at the Ashland library in the next few months.

Ashland resident, author and anthropologist Nina Egert has been a lay environmentalist since the early 1970s. Act Locally appears the first and third Mondays of the month in the Tidings.

Geology Professor Karen Grove presents a PowerPoint talk on climate change as recorded in the Earth's sedimentary layers. Photo by Nina Egert