(Press-News.org) BOULDER –-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. The study, by National Center for Atmospheric Research (NCAR) scientist Jeffrey Kiehl, will appear as a "Perspectives" piece in this week's issue of the journal Science.
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, when global temperatures averaged about 29 degrees Fahrenheit (16 degrees Celsius) above pre-industrial levels.
Kiehl said that global temperatures may gradually rise over centuries or millennia in response to the carbon dioxide. The elevated levels of carbon dioxide may remain in the atmosphere for tens of thousands of years, according to recent computer model studies of geochemical processes that the study cites.
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 than 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. The work was funded by the National Science Foundation, NCAR's sponsor.
Learning from Earth's past
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 on 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 degrees F (5-10 degrees C) above present-day temperatures. The polar regions were some 27-36 degrees F (15-20 degrees 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 degrees F (31 degrees C)—substantially higher than the pre-industrial average temperature of about 59 degrees F (15 degrees C).
Twice the heat?
The study also found that carbon dioxide may have at least twice the 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 degree C 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 degrees 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 discrepency 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.
INFORMATION:
The University Corporation for Atmospheric Research manages the National Center for Atmospheric Research under sponsorship by the National Science Foundation. Any opinions, findings and conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.
Journalists who agree to abide by the embargo may request advance copies of the article by calling the Office of Public Programs at the American Association for the Advancement of Science at 202-326-6440 or sending an email to scipak@aaas.org.
About the article
Title:
Lessons from Earth's Past
Author:
Jeffrey Kiehl
Publication:
Science, January 14, 2011
Earth's hot past could be prologue to future climate
2011-01-14
ELSE PRESS RELEASES FROM THIS DATE:
Aerosols transmit prions to mice, causing disease
2011-01-14
Scientists at the University of Zurich (Switzerland) and the Federal Research Institute for Animal Health (FLI; Tuebingen) have challenged the notion that airborne prions are innocuous.Details of how inhalation of prion-tainted aerosols induced disease are published January 13 in the open-access journal PLoS Pathogens.
It is known that prions can be transmitted through contaminated surgical instruments and, more rarely, through blood transfusions. However, prions are not generally considered to be airborne - in contrast to many viruses such as influenza and chicken pox.
In ...
New measures could improve quality of care at stroke centers
2011-01-14
The American Heart Association/American Stroke Association has proposed metrics that healthcare professionals can use to monitor the diagnosis and treatment of patients at stroke centers to help improve the quality of care stroke patients receive. The recommendations are published in a scientific statement in Stroke: Journal of the American Heart Association.
The metrics are being proposed to assist in the standardized designation of Comprehensive Stroke Centers. These centers would be expected to monitor new diagnostic and treatment metrics, in addition to the standard ...
Room light before bedtime may impact sleep quality, blood pressure and diabetes risk
2011-01-14
Chevy Chase, MD—According to a recent study accepted for publication in The Endocrine Society's Journal of Clinical Endocrinology & Metabolism (JCEM), exposure to electrical light between dusk and bedtime strongly suppresses melatonin levels and may impact physiologic processes regulated by melatonin signaling, such as sleepiness, thermoregulation, blood pressure and glucose homeostasis.
Melatonin is a hormone produced at night by the pineal gland in the brain. In addition to its role in regulating the sleep-wake cycle, melatonin has been shown to lower blood pressure ...
Women with polycystic ovary syndrome may be more vulnerable to BPA
2011-01-14
Chevy Chase, MD—A recent study accepted for publication in The Endocrine Society's Journal of Clinical Endocrinology & Metabolism (JCEM), found higher Bisphenol A (BPA) levels in women with polycystic ovary syndrome (PCOS) compared to controls. Furthermore, researchers found a statistically significant positive association between male sex hormones and BPA in these women suggesting a potential role of BPA in ovarian dysfunction.
BPA is a very common industrial compound used in food and drink packaging, plastic consumer products and dental materials. PCOS is the most ...
Race plays role in weight-related counseling among obese patients
2011-01-14
When it comes to advising obese patients, blacks receive less weight reduction and exercise counseling from physicians than their white counterparts. This is according to a recent study conducted by researchers at the Johns Hopkins Bloomberg School of Public Health who examined the impact of patient and doctor race concordance on weight-related counseling. The results are featured in the January 2011 online issue of Obesity.
"Contrary to our expectations, we did not observe a positive association between patient-physician race concordance and weight-related counseling," ...
When continents formed
2011-01-14
The continental crust is the principal record of conditions on the Earth for the last 4.4 billion years. Its formation modified the composition of the mantle and the atmosphere, it supports life, and it remains a sink for carbon dioxide through weathering and erosion. The continental crust therefore has had a key role in the evolution of the Earth, and yet the timing of its generation remains the topic of considerable debate.
It is widely believed that the juvenile continental crust has grown from the depleted upper mantle. One common way to assess when new crust was ...
Researchers can predict your video game aptitude by imaging your brain
2011-01-14
CHAMPAIGN, Ill. — Researchers report that they can predict "with unprecedented accuracy" how well you will do on a complex task such as a strategic video game simply by analyzing activity in a specific region of your brain.
The findings, published in the online journal PLoS ONE, offer detailed insights into the brain structures that facilitate learning, and may lead to the development of training strategies tailored to individual strengths and weaknesses.
The new approach used established brain imaging techniques in a new way. Instead of measuring how brain activity ...
BSE pathogens can be transmitted by air
2011-01-14
Airborne prions are also infectious and can induce mad cow disease or Creutzfeldt-Jakob disorder. This is the surprising conclusion of researchers at the University of Zurich, the University Hospital Zurich and the University of Tübingen. They recommend precautionary measures for scientific labs, slaughterhouses and animal feed plants.
The prion is the infectious agent that caused the epidemic of mad cow disease, also termed bovine spongiform encephalopathy (BSE), and claimed the life of over 280,000 cows in the past decades. Transmission of BSE to humans, e.g. by ...
New predator 'dawn runner' discovered in early dinosaur graveyard
2011-01-14
A team of paleontologists and geologists from Argentina and the United States on Jan. 13 announced the discovery of a lanky dinosaur that roamed South America in search of prey as the age of dinosaurs began, approximately 230 million years ago.
Sporting a long neck and tail and weighing only 10 to 15 pounds, the new dinosaur has been named Eodromaeus, the "dawn runner."
"It really is the earliest look we have at the long line of meat eaters that would ultimately culminate in Tyrannosaurus rex near the end of the dinosaur era," said Paul Sereno, University of Chicago ...
Academics urge universities to change culture to value teaching as highly as research
2011-01-14
Irvine, Calif. — The reward systems at universities heavily favor science, math and engineering research at the expense of teaching, which can and must change. That's the conclusion of UC Irvine biology professor Diane K. O'Dowd and research professors at Harvard University, Yale University, the Massachusetts Institute of Technology, and elsewhere.
Writing in the Jan. 14 issue of Science magazine, the authors note that professors have two responsibilities: to generate new knowledge and to educate students. But, they maintain, "although education and lifelong learning ...