Tag Archives: paleoclimate

Water Supply, Drought and Climate Change at Mono Lake

This post was first published on Dec. 6, 2013, on the Earth Institute’s State of the Planet blog. It was updated on Oct. 14, 2014 (see below).

Guleed Ali pauses to study his notebook, standing on a steep slope covered in gray volcanic ash and desert brush, high above the present-day shore of Mono Lake in eastern California. He looks across the slope to where, a few hundred yards away, a gash of lighter gray sediment cuts across the hill, then disappears. The exposed sediment is history: A record of deposits left by Mono Lake when it stood far higher than today.

Ali picks a spot, hefts his shovel and begins clawing into the slope, raising puffs of dust, searching for a missing page in that sediment history: something higher upslope, evidence of the stream that would have fed the prehistoric lake: a layer of gravel. He finds only sand – perhaps an ancient beach. He moves across the slope, lifts and plunges his shovel back into the soft hillside.

Mono Lake, Lamont-Doherty Earth Observatory, Guleed Ali

By studying stream bed sediments, Guleed Ali tries to build a history of how water levels have changed at Mono Lake. Photo: D. Funkhouser

He is digging for dates, looking back tens of thousands of years into the last ice age: When was the lake higher? When did it shrink, and grow again? How does that chronology correspond with the advance and retreat of the massive ice sheets that covered much of North America? And how did the lake’s levels respond to changing climate?

Understanding that past will help scientists like Ali, a PhD student at Lamont-Doherty Earth Observatory, project what might happen in the future as the world warms up. This is no esoteric question for Los Angeles, whose nearly 4 million people depend in part on Mono Lake’s watershed for drinking water, green lawns, agriculture and industry.

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From Distant Past, Lessons on Ocean Acidification

First posted Dec. 8, 2011 on the Earth Institute’s State of the Planet blog.

foraminifera, Paleocene-Eocene Thermal Maximum, extinction

A core section shows shells of foraminifera, and reduced carbonate preservation, at the Paleocene-Eocene Thermal Maximum. During the period, researchers believe up to half of deep-sea benthic foraminifer species suffered extinction. Photo: Laura Foster, University of Bristol

Oceans turned more acidic during a period of great warming some 56 million years ago, leading to an extinction of bottom-dwelling marine species known as foraminifera, a scenario that could be repeated as a result of human-induced global warming today, only much more quickly.

To better understand what could happen in the near future, geochemist Bärbel Hönisch of the Lamont-Doherty Earth Observatory and a few colleagues studied ocean acidity events over the past 250 million years to confirm whether acidification took place during periods of global warming. The conditions of one period in particular – the Paleocene-Eocene Thermal Maximum — were similar to the worst-case scenarios scientists project for future climate change.

“The earlier changes affected the biology, so we’d expect that would happen today,” Hönisch said. She doesn’t like to speculate on precisely what the impact might be; some creatures may disappear, others may adapt.

“I don’t think it will destroy the earth — the earth will cope with us,” she said. “We may not like what happens.” Hönisch gave a talk on her research today at the fall meeting of the American Geophysical Union in San Francisco, as part of a broader discussion there of findings related to ocean acidification.

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Rhone Glacier Finely Tuned to Climate Changes

Rhone Glacier, Swiss Alps

The Rhone Glacier in 1900 and 2008. Residents of the village of Gletsch, down the valley from the glacier, have kept track of the ice since 1602. “Their water supply, the availability of farmland is controlled by where the glacier is,” researcher Brent Goehring said. (Photos: http://www.swisseduc.ch/glaciers/index-en.html)

First published on the Earth Institute’s State of the Planet blog on June 3, 2011

During the last ice age, the Rhone Glacier was the dominant glacier in the Alps, covering a significant part of Switzerland. Over the next 11,500 years or so, the glacier, which forms the headwaters of the Rhone River, has been shrinking and growing again in response to shifts in climate.

Until now, scientists have had no accurate way of knowing the long-term history of the glacier. Local records of the ice date back to 1602, and it is clear that the Rhone, like other glaciers in the Alps, has retreated dramatically in the past 150 years. This melting has exposed intriguing clues – remnants of trees from once-forested land, and artifacts of human settlements dating back thousands of years, to times when even more of the land was uncovered and green.

A team of researchers led by two scientists from the Lamont-Doherty Earth Observatory have found a novel method to measure this crucial back-and-forth, by measuring isotopes in hunks of stone chipped out from recently exposed bedrock near the edge of the ice. They found that for most of the Holocene Epoch, dating from the end of the last ice age about 11,500 years ago to the present, the Rhone Glacier has been smaller than it is today.

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Tree Rings Open Door to El Niño’s Past

First published on the Earth Institute website on May 26, 2011.

Bristlecone trees, such as this over 1,000-year-old tree in the Great Basin National Park, contributed to the tree ring record on El Niño. Photo courtesy Gisela Speidel, IPRC

Bristlecone trees, such as this over 1,000-year-old tree in the Great Basin National Park, contributed to the tree ring record on El Niño. Photo courtesy Gisela Speidel, IPRC

El Niño and La Niña, the periodic shifts in Pacific Ocean temperatures, affect weather around the globe, and many scientists have speculated that a warming planet will make those fluctuations more volatile, bringing more intense drought or extreme rainfall to various regions.

Now, scientists have used tree-ring data from the American Southwest to reconstruct a 1,100-year history of the cycle that backs up that assertion. The researchers found a 50-90-year cycle of waxing and waning El Niño intensity that shows that, when the earth warms, the climate acts up.

“Our work revealed that the towering trees on the mountain slopes of the U.S. Southwest and the colorful corals in the tropical Pacific both listen to the music of El Niño, which shows its signature in their yearly growth rings,” explains Jinbao Li, the paper’s lead author and a former PhD student at Lamont-Doherty Earth Observatory.

The research, published May 6 in Nature Climate Change, will improve scientists’ ability to predict future climate and the effects of global warming, the scientists say.

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