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EARLY EARTH
Does Earth Hot Past Offers A Glimpse Into The Future

Building A Global Thermostat In L1
Bethesda MD (SPX) Feb 14, 2011 - The sun is the predominant source of energy for the Earth. While there are long- and short-term variations in solar intensity that effect periodic global climate changes, there is also a secular temperature increase as the sun ages. Fortunately, the rate of increase is very low and we will not notice a significant change for at least thousands of years. Nevertheless, if we are to counter inevitable global warming the planning process must start soon, as any solution will likely require many centuries of implementation. We do know that three to four billion years ago the sun emitted only 70% as much power as it does today. Had the atmospheric composition been what it is today, liquid water would not have existed on Earth. Nevertheless, there is evidence that water was present at that time.

In order for this to be true, theory tells us that there had to have been a much different atmosphere, one with much higher concentrations of greenhouse gases. Over the subsequent roughly three billion years, the sun's energy output increased, causing changes in the atmospheric composition. The primary effect was the oxygenation of the atmosphere. Short-term variations in the sun's output include the well-known 11-year solar cycle. Long-term variations are thought to have influenced the Little Ice Age, and some of the warming trends noted from 1900 to 1950. Obviously, solar dynamics are not fully understood, but we hope to learn more over the coming decades with space experiments such as NASA's STEREO and Solar Probe Plus missions.

In the near-term, the human race is relatively safe from natural processes such as increased solar heating. Over the next 100,000 years or so, conditions will change significantly. Average temperatures will rise. Sea levels will also rise, causing a reduction in dry land areas. The atmosphere will change in ways that may require modifications of the way we live and breathe. A million years from now solar output may have increased enough to make Earth unlivable by todays standards. How can we counter this effect? Any solution will require long-term planning and execution. The required expenditures will surely be huge on a world economic scale. However, the alternative to action may be the end of the human race. The Earth will need a thermostat to control incoming solar energy.

One approach may be the placement of a huge sun shield at the L1 Earth-Sun libration point. This is one of five points of gravitational equilibrium in the rotating Earth-Sun coordinate frame. L1 is particularly attractive for the positioning of a shield, because the positioning control requirements are minimal and this point is in the Earth-Sun line of sight at about 1.5 million km from Earth. This is a long-term project, since any solar shield would require a cross sectional area of at least several million square kilometers. Such a shield could be articulated to vary the shading effect as solar radiation varies over time. This idea may seem ridiculous today, but we do know that the sun will continue to warm. Some action will eventually be required to preserve the race. If you have a better idea, please let us know at [email protected].
by Staff Writers
Washington DC (SPX) Feb 14, 2011
The magnitude of climate change during Earth's deep past suggests that future temperatures may eventually rise far more than projected if society continues its pace of emitting greenhouse gases, a new analysis concludes. Studying Earth's climate is an essential step for astrobiologists attempting to determine the potential future habitability of our planet and the consequences that climate change may bring for life on Earth.

The study, by National Center for Atmospheric Research (NCAR) scientist Jeffrey Kiehl, appears as a "Perspectives" article in the journal Science. The work was funded by the National Science Foundation (NSF), NCAR's sponsor.

Building on recent research, the study examines the relationship between global temperatures and high levels of carbon dioxide in the atmosphere tens of millions of years ago.

It warns that, if carbon dioxide emissions continue at their current rate through the end of this century, atmospheric concentrations of the greenhouse gas will reach levels that existed about 30 million to 100 million years ago. Global temperatures then averaged about 29 degrees Fahrenheit (16 degrees Celsius) above pre-industrial levels. Kiehl said that global temperatures may take centuries or millennia to fully adjust in response to the higher carbon dioxide levels.

Accorning to the study and based on recent computer model studies of geochemical processes, elevated levels of carbon dioxide may remain in the atmosphere for tens of thousands of years. The study also indicates that the planet's climate system, over long periods of times, may be at least twice as sensitive to carbon dioxide as currently projected by computer models, which have generally focused on shorter-term warming trends.

This is largely because even sophisticated computer models have not yet been able to incorporate critical processes, such as the loss of ice sheets, that take place over centuries or millennia and amplify the initial warming effects of carbon dioxide.

"If we don't start seriously working toward a reduction of carbon emissions, we are putting our planet on a trajectory that the human species has never experienced," says Kiehl, a climate scientist who specializes in studying global climate in Earth's geologic past. "We will have committed human civilization to living in a different world for multiple generations."

The Perspectives article pulls together several recent studies that look at various aspects of the climate system, while adding a mathematical approach by Kiehl to estimate average global temperatures in the distant past. Its analysis of the climate system's response to elevated levels of carbon dioxide is supported by previous studies that Kiehl cites.

"This research shows that squaring the evidence of environmental change in the geologic record with mathematical models of future climate is crucial," says David Verardo, Director of NSF's Paleoclimate Program. "Perhaps Shakespeare's words that 'what's past is prologue' also apply to climate."

Kiehl focused on a fundamental question: when was the last time Earth's atmosphere contained as much carbon dioxide as it may by the end of this century? If society continues its current pace of increasing the burning of fossil fuels, atmospheric levels of carbon dioxide are expected to reach about 900 to 1,000 parts per million by the end of this century.

That compares with current levels of about 390 parts per million, and pre-industrial levels of about 280 parts per million. Since carbon dioxide is a greenhouse gas that traps heat in Earth's atmosphere, it is critical for regulating Earth's climate.

Without carbon dioxide, the planet would freeze over. But as atmospheric levels of the gas rise, which has happened at times in the geologic past, global temperatures increase dramatically and additional greenhouse gases, such as water vapor and methane, enter the atmosphere through processes related to evaporation and thawing. This leads to further heating.

Kiehl drew on recently published research that, by analyzing molecular structures in fossilized organic materials, showed that carbon dioxide levels likely reached 900 to 1,000 parts per million about 35 million years ago. At that time, temperatures worldwide were substantially warmer than at present, especially in polar regions--even though the Sun's energy output was slightly weaker.

The high levels of carbon dioxide in the ancient atmosphere kept the tropics at about 9-18 F (5-10 C) above present-day temperatures. The polar regions were some 27-36 F (15-20 C) above present-day temperatures. Kiehl applied mathematical formulas to calculate that Earth's average annual temperature 30 to 40 million years ago was about 88 F (31 C) - substantially higher than the pre-industrial average temperature of about 59 F (15 C).

The study also found that carbon dioxide may have two times or more an effect on global temperatures than currently projected by computer models of global climate. The world's leading computer models generally project that a doubling of carbon dioxide in the atmosphere would have a heating impact in the range of 0.5 to 1.0 degrees Celsius watts per square meter. (The unit is a measure of the sensitivity of Earth's climate to changes in greenhouse gases.)

However, the published data show that the comparable impact of carbon dioxide 35 million years ago amounted to about 2 C watts per square meter. Computer models successfully capture the short-term effects of increasing carbon dioxide in the atmosphere.

But the record from Earth's geologic past also encompasses longer-term effects, which accounts for the discrepancy in findings. The eventual melting of ice sheets, for example, leads to additional heating because exposed dark surfaces of land or water absorb more heat than ice sheets.

"This analysis shows that on longer time scales, our planet may be much more sensitive to greenhouse gases than we thought," Kiehl says.

Climate scientists are currently adding more sophisticated depictions of ice sheets and other factors to computer models. As these improvements come on-line, Kiehl believes that the computer models and the paleoclimate record will be in closer agreement, showing that the impacts of carbon dioxide on climate over time will likely be far more substantial than recent research has indicated.

Because carbon dioxide is being pumped into the atmosphere at a rate that has never been experienced, Kiehl could not estimate how long it would take for the planet to fully heat up. However, a rapid warm-up would make it especially difficult for societies and ecosystems to adapt, he says. If emissions continue on their current trajectory, "the human species and global ecosystems will be placed in a climate state never before experienced in human history," the paper states.



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