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You would have to go back at least 15 million years to find carbon dioxide levels on Earth as high as they are today, a UCLA scientist and colleagues report Oct. 8 in the online edition of the journal Science.

“The last time carbon dioxide levels were apparently as high as they are today — and were sustained at those levels — global temperatures were 5 to 10 degrees Fahrenheit higher than they are today, the sea level was approximately 75 to 120 feet higher than today, there was no permanent sea ice cap in the Arctic and very little ice on Antarctica and Greenland,” said the paper’s lead author, Aradhna Tripati, a UCLA assistant professor in the department of Earth and space sciences and the department of atmospheric and oceanic sciences.

“Carbon dioxide is a potent greenhouse gas, and geological observations that we now have for the last 20 million years lend strong support to the idea that carbon dioxide is an important agent for driving climate change throughout Earth’s history,” she said.

By analyzing the chemistry of bubbles of ancient air trapped in Antarctic ice, scientists have been able to determine the composition of Earth’s atmosphere going back as far as 800,000 years, and they have developed a good understanding of how carbon dioxide levels have varied in the atmosphere since that time. But there has been little agreement before this study on how to reconstruct carbon dioxide levels prior to 800,000 years ago.

Tripati, before joining UCLA’s faculty, was part of a research team at England’s University of Cambridge that developed a new technique to assess carbon dioxide levels in the much more distant past — by studying the ratio of the chemical element boron to calcium in the shells of ancient single-celled marine algae. Tripati has now used this method to determine the amount of carbon dioxide in Earth’s atmosphere as far back as 20 million years ago.

“We are able, for the first time, to accurately reproduce the ice-core record for the last 800,000 years — the record of atmospheric C02 based on measurements of carbon dioxide in gas bubbles in ice,” Tripati said. “This suggests that the technique we are using is valid.

“We then applied this technique to study the history of carbon dioxide from 800,000 years ago to 20 million years ago,” she said. “We report evidence for a very close coupling between carbon dioxide levels and climate. When there is evidence for the growth of a large ice sheet on Antarctica or on Greenland or the growth of sea ice in the Arctic Ocean, we see evidence for a dramatic change in carbon dioxide levels over the last 20 million years.

“A slightly shocking finding,” Tripati said, “is that the only time in the last 20 million years that we find evidence for carbon dioxide levels similar to the modern level of 387 parts per million was 15 to 20 million years ago, when the planet was dramatically different.”

Levels of carbon dioxide have varied only between 180 and 300 parts per million over the last 800,000 years — until recent decades, said Tripati, who is also a member of UCLA’s Institute of Geophysics and Planetary Physics. It has been known that modern-day levels of carbon dioxide are unprecedented over the last 800,000 years, but the finding that modern levels have not been reached in the last 15 million years is new.

Prior to the Industrial Revolution of the late 19th and early 20th centuries, the carbon dioxide level was about 280 parts per million, Tripati said. That figure had changed very little over the previous 1,000 years. But since the Industrial Revolution, the carbon dioxide level has been rising and is likely to soar unless action is taken to reverse the trend, Tripati said.

“During the Middle Miocene (the time period approximately 14 to 20 million years ago), carbon dioxide levels were sustained at about 400 parts per million, which is about where we are today,” Tripati said. “Globally, temperatures were 5 to 10 degrees Fahrenheit warmer, a huge amount.”

Tripati’s new chemical technique has an average uncertainty rate of only 14 parts per million.

“We can now have confidence in making statements about how carbon dioxide has varied throughout history,” Tripati said.

In the last 20 million years, key features of the climate record include the sudden appearance of ice on Antarctica about 14 million years ago and a rise in sea level of approximately 75 to 120 feet.

“We have shown that this dramatic rise in sea level is associated with an increase in carbon dioxide levels of about 100 parts per million, a huge change,” Tripati said. “This record is the first evidence that carbon dioxide may be linked with environmental changes, such as changes in the terrestrial ecosystem, distribution of ice, sea level and monsoon intensity.”

Today, the Arctic Ocean is covered with frozen ice all year long, an ice cap that has been there for about 14 million years.

“Prior to that, there was no permanent sea ice cap in the Arctic,” Tripati said.

Some projections show carbon dioxide levels rising as high as 600 or even 900 parts per million in the next century if no action is taken to reduce carbon dioxide, Tripati said. Such levels may have been reached on Earth 50 million years ago or earlier, said Tripati, who is working to push her data back much farther than 20 million years and to study the last 20 million years in detail.

More than 50 million years ago, there were no ice sheets on Earth, and there were expanded deserts in the subtropics, Tripati noted. The planet was radically different.

Co-authors on the Science paper are Christopher Roberts, a Ph.D. student in the department of Earth sciences at the University of Cambridge, and Robert Eagle, a postdoctoral scholar in the division of geological and planetary sciences at the California Institute of Technology.

The research was funded by UCLA’s Division of Physical Sciences and the United Kingdom’s National Environmental Research Council.

Tripati’s research focuses on the development and application of chemical tools to study climate change throughout history. She studies the evolution of climate and seawater chemistry through time.

“I’m interested in understanding how the carbon cycle and climate have been coupled, and why they have been coupled, over a range of time-scales, from hundreds of years to tens of millions of years,” Tripati said.

In addition to being published on the Science Express website, the paper will be published in the print edition of Science at a later date

Source: ScienceDaily

A new technique that tapped previously inaccessible supplies of natural gas in the United States is spreading to the rest of the world, raising hopes of a huge expansion in global reserves of the cleanest fossil fuel.

Italian and Norwegian oil engineers and geologists have arrived in Texas, Oklahoma and Pennsylvania to learn how to extract gas from layers of a black rock called shale. Companies are leasing huge tracts of land across Europe for exploration. And oil executives are gathering rocks and scrutinizing Asian and North African geological maps in search of other fields.

The global drilling rush is still in its early stages. But energy analysts are already predicting that shale could reduce Europe’s dependence on Russian natural gas. They said they believed that gas reserves in many countries could increase over the next two decades, comparable with the 40 percent increase in the United States in recent years.

“It’s a breakout play that is going to identify gigantic resources around the world,” said Amy Myers Jaffe, an energy expert at Rice University. “That will change the geopolitics of natural gas.

More extensive use of natural gas could aid in reducing global warming, because gas produces fewer emissions of greenhouse gases than either oil or coal. China and India, which have growing economies that rely heavily on coal for electricity, appear to have large potential for production of shale gas. Larger gas reserves would encourage developing countries to convert more of their transportation fleets to use natural gas rather than gasoline.

Shale is a sedimentary rock rich in organic material that is found in many parts of the world. It was of little use as a source of gas until about a decade ago, when American companies developed new techniques to fracture the rock and drill horizontally.

Because so little drilling has been done in shale fields outside of the United States and Canada, gas analysts have made a wide array of estimates for how much shale gas could be tapped globally. Even the most conservative estimates are enormous, projecting at least a 20 percent increase in the world’s known reserves of natural gas.

One recent study by IHS Cambridge Energy Research Associates, a consulting group, calculated that the recoverable shale gas outside of North America could turn out to be equivalent to 211 years’ worth of natural gas consumption in the United States at the present level of demand, and maybe as much as 690 years. The low figure would represent a 50 percent increase in the world’s known gas reserves, and the high figure, a 160 percent increase.

The projections suggest that the new method of producing gas “is the biggest energy innovation of the decade,” said Daniel Yergin, chairman of the Cambridge consulting group. “And the amazing thing is there was no grand opening ceremony for it. It just snuck up.”

Over the last five years, production of gas from shale has spread across wide swaths of Texas, Louisiana and Pennsylvania. All the new production has produced a glut of gas in the United States, helping to drive down gas prices and utility costs.

Now American companies are looking abroad for lucrative shale fields in countries hungry for more energy. They are focusing particularly on Europe, where gas prices are sometimes twice what they are in the United States, and large shale beds are located close to some cities.

Exxon Mobil has drilled a few exploratory wells in Germany in recent months. Devon Energy is teaming up with Total, the French oil company, seeking approval to drill in France. ConocoPhillips announced recently that it had signed an agreement with a subsidiary of a small British firm to explore a million acres in the Baltic Basin of Poland.

Early estimates of recoverable European shale gas resources range up to 400 trillion cubic feet, less than half the industry’s estimates of what is recoverable in the United States. But European energy executives say they are excited about the prospects because the Continent’s conventional gas reserves are too small to meet demand.

Source: NYT