Science Current Events | Science News | Brightsurf.com
 

In new study, ancient and modern evidence suggests limits to future global warming

April 20, 2006
DURHAM, N.C. - Instrumental readings made during the past century offer ample evidence that carbon dioxide and other "greenhouse gases" in the atmosphere are warming Earth's climate, a team led by Duke University scientists has reported. But by analyzing indirect evidence of temperature fluctuations over six previous centuries, the team also found that the magnitude of future global warming will likely fall well short of current highest predictions.

In making their deductions, the researchers ran some 1,000 computer simulations, covering 1,000 years, that took into account a range of modern and ancient climate records. Modern records are based on thermometer readings, while measurements derived from such sources as tree rings and ice cores served as markers of warm and cold spells over prior centuries.

The investigators evaluated the data using an "energy balance model" that they describe as a slimmed-down version of the heavy-duty computer models typically used to analyze climate trends. It is the model's streamlined nature that enabled the researchers to perform such large numbers of simulations over such a long period in such detail, they said.

The group used thousands of different versions of this model, each version varying in some of its properties, in order to determine which variants best matched actual observations. One key property that varied was what the researchers termed "sensitivity" - that is, how much the simulations' temperatures would change in response to increasing greenhouse gas levels.

"What I can say very confidently is that the present-day sensitivity is not zero, meaning that there is a positive, warming response to greenhouse gases," said climate analyst Gabriele Hegerl, an associate research professor at Duke's Nicholas School of the Environment and Earth Sciences. "Our work also substantially reduces the probability of very high climate sensitivities."

Hegerl is lead author of the study, published April 20, 2006, in the journal Nature. Her co-authors are Thomas Crowley, Duke's Nicholas Professor of Earth Systems Science; William Hyde, a former Nicholas School research scientist now at the University of Toronto; and David Frame, a researcher at the University of Oxford.

Their work was supported by the National Oceanic and Atmospheric Administration, the U.S. Department of Energy and the National Science Foundation.

Many scientists expect that the level of carbon dioxide in the atmosphere will sometime this century reach double the levels that were present during preindustrial times. Because carbon dioxide traps outgoing heat energy similarly to the glass in a greenhouse, the additional human-created outputs of the gas - mostly from fossil-fuel burning - are expected to warm Earth's climate. The key question is: by how much?

The commonly accepted range for how much average global temperatures will rise in response to a doubling of atmospheric carbon dioxide is between 1.5 and 4.5 degrees centigrade, according to the researchers. But some observational studies, they noted, suggest the possibility that average temperatures might rise more than 9 degrees.

However, the new study - using "reconstructions" of Northern Hemisphere temperatures since the year 1270 - indicates a 90 percent probability that a doubling of carbon dioxide levels will result in temperature increases of between 1.5 and 6.2 degrees, the team reported.

In turn, the study showed a reduced likelihood that the actual maximum increase will exceed 4.5 degrees - "from 36 percent to 15 percent or less," the researchers said. A 4.5 degree increase is the highest maximum currently predicted by the international Intergovernmental Panel on Climate Change.

Hegerl said her group confined its study largely to the Northern Hemisphere because only there have scientists collected enough data to reconstruct temperature variations over the entire past millennium.

According to Hegerl, some studies claim that preindustrial temperatures fluctuated very little until the past century, and have risen sharply since.

"But our reconstruction supports a lot of variability in the past, as well as an upward trend in the 20th century," she said. And a record with plenty of ups and downs before the modern era "shows a climate reacting then and now to a variety of 'external forcing,'" she said.

The term "external forcing" refers to all those outside influences that can perturb the climate. Understanding how temperatures responded to such forcings in the premodern era - when the impact of carbon dioxide and other heat-trapping gases varied relatively little - helps scientists predict future forcings by greenhouse gases, Hegerl said.

"Looking back longer in time makes it possible to more confidently rule out responses that are very high or very low," she said.

The researchers consulted instrumental records of the various forcings that have occurred in modern times, with the aim of comparing those to actual recorded temperatures.

In order to reconstruct temperatures from the centuries before 1850, the team used various lines of indirect evidence. They looked, for example, at particulates trapped in ice cores as measures of past volcanic eruptions. Such eruptions eject clouds of particles high into the atmosphere. By reducing the amount of sunlight that can pass through the atmosphere, the particles tend to cool the climate for a time, Hegerl said.

They also consulted a number of tree ring studies that reveal hot and cold spells in ancient growth variations, as well as studies that can estimate temperatures as far back as the 1600s based on readings obtained from holes bored deep into the ground.

Although the researchers collected data spanning a full millennium, because of some technical limitations they actually simulated temperature variations over a roughly 700-year period beginning in 1270.

All in all, the researchers considered four different detailed reconstructions of past climates, including a new reconstruction done by Crowley and Hegerl, to deduce probable temperatures before reliable instruments were available.

According to Hegerl, past volcanic eruptions provided the strongest tie between past climate forcings and temperatures. "You can see downturns in temperature exactly where you see volcanic eruptions," she said.

Duke University


Related Global Warming Current Events and Global Warming News Articles


Politics Divide Coastal Residents' Views of Environment, UNH Research Finds
From the salmon-rich waters of Southeast Alaska to the white sand beaches of Florida's Gulf Coast to Downeast Maine's lobster, lumber and tourist towns, coastal residents around the U.S. share a common characteristic: their views about coastal environments divide along political lines.

Researchers discover new producer of crucial vitamin
New research has determined that a single group of micro-organisms may be responsible for much of the world's vitamin B12 production in the oceans, with implications for the global carbon cycle and climate change.

Asian monsoon much older than previously thought
The Asian monsoon already existed 40 million years ago during a period of high atmospheric carbon dioxide and warmer temperatures, reports an international research team led by a University of Arizona geoscientist.

Last decade's slow-down in global warming enhanced by an unusual climate anomaly
A hiatus in global warming ongoing since 2001 is due to a combination of a natural cooling phase, known as multidecadal variability (MDV) and a downturn of the secular warming trend.

The ozone hole has stabilized - some questions remain
The production and consumption of chemical substances threatening the ozone layer has been regulated since 1987 in the Montreal Protocol. Eight international expert reports have since been published, which examine the current situation and the future of the threat to the ozone layer.

Yale Study Shows How Conversion Of Forests to Cropland Affected Climate
The conversion of forests into cropland worldwide has triggered an atmospheric change that, while seldom considered in climate models, has had a net cooling effect on global temperatures, according to a new Yale study.

Study resolves discrepancy in Greenland temperatures during end of last ice age
A new study of three ice cores from Greenland documents the warming of the large ice sheet at the end of the last ice age - resolving a long-standing paradox over when that warming occurred.

To clean air and beyond: Catching greenhouse gases with advanced membranes
Researchers in Japan have engineered a membrane with advanced features capable of removing harmful greenhouse gases from the atmosphere.

Why global warming is taking a break
Global warming is currently taking a break: whereas global temperatures rose drastically into the late 1990s, the global average temperature has risen only slightly since 1998 - surprising, considering scientific climate models predicted considerable warming due to rising greenhouse gas emissions.

Exporting US coal to Asia could drop emissions 21 percent
Under the right scenario, exporting U.S. coal to power plants in South Korea could lead to a 21 percent drop in greenhouse gas emissions compared to burning the fossil fuel at plants in the United States, according to a new Duke University-led study.
More Global Warming Current Events and Global Warming News Articles

Climate Change: Evidence and Causes (PDF Booklet)

Climate Change: Evidence and Causes (PDF Booklet)
by National Academies Press


Climate Change: Evidence and Causes is a jointly produced publication of The US National Academy of Sciences and The Royal Society. Written by a UK-US team of leading climate scientists and reviewed by climate scientists and others, the publication is intended as a brief, readable reference document for decision makers, policy makers, educators, and other individuals seeking authoritative information on the some of the questions that continue to be asked. Climate Change makes clear what is well-established and where understanding is still developing. It echoes and builds upon the long history of climate-related work from both national academies, as well as on the newest climate-change assessment from the United Nations' Intergovernmental Panel on Climate Change. It touches on current...

Global Warming: Understanding the Forecast

Global Warming: Understanding the Forecast
by David Archer (Author)


Archer's Global Warming: Understanding the Forecast 2nd Edition, is the first real text to present the science and policy surrounding climate change at the right level. Accompanying videos, simulations and instructional support makes it easier to build a syllabus to improve and create new material on climate change. Archer's polished writing style makes the text entertaining while the improved pedagogy helps better understand key concepts, ideas and terms.This edition has been revised and reformulated with a new chapter template of short chapter introductions, study questions at the end, and critical thinking puzzlers throughout. Also a new asset for the BCS was created that will give ideas for assignments and topics for essays and other projects. Furthermore, a number of interactive...

Global Warming

Global Warming
by Seymour Simon (Author)


Award-winning science writer Seymour Simon gives you a full-color photographic introduction to the causes and effects of global warming and climate change. Earth's climate has always varied, but it is now changing more rapidly than at any other time in recent centuries. The climate is very complex, and many factors play important roles in determining how it changes. Why is the climate changing? Could Earth be getting warmer by itself? Are people doing things that make the climate warmer?Supports the Common Core State Standards

The Great Global Warming Blunder: How Mother Nature Fooled the World’s Top Climate Scientists

The Great Global Warming Blunder: How Mother Nature Fooled the World’s Top Climate Scientists
by Roy W Spencer (Author)


The Great Global Warming Blunder unveils new evidence from major scientific findings that explode the conventional wisdom on climate change and reshape the global warming debate as we know it. Roy W. Spencer, a former senior NASA climatologist, reveals how climate researchers have mistaken cause and effect when analyzing cloud behavior and have been duped by Mother Nature into believing the Earth’s climate system is far more sensitive to human activities and carbon dioxide than it really is.

In fact, Spencer presents astonishing new evidence that recent warming is not the fault of humans, but the result of chaotic, internal natural cycles that have been causing periods of warming and cooling for millennia. More carbon dioxide in the atmosphere is not necessarily to be feared; The...

The Global Warming Reader: A Century of Writing About Climate Change

The Global Warming Reader: A Century of Writing About Climate Change
by Bill McKibben (Author)


Our most widely respected environmental writer brings together the essential voices on global warming, from its 19th-century discovery to the present
With the rise of extreme weather events worldwide--witness the devastation wrought by Hurricanes Sandy, Irene, and Katrina, and the sustained drought across the American West--global warming has become increasingly difficult to deny.

What is happening to our planet? And what can we do about it? The Global Warming Reader provides more than thirty-five answers to these burning questions, from more than one hundred years of engagement with the topic. Here is Elizabeth Kolbert's groundbreaking essay "The Darkening Sea," Michael Crichton's skeptical view of climate change, George Monbiot's biting indictment of those who are...

The Age of Global Warming: A History

The Age of Global Warming: A History
by Rupert Darwall (Author)


Rachel Carson's epoch-creating Silent Spring marked the beginnings of the environmental movement in the 1960s, its 'First Wave' peaking at the 1972 Stockholm Conference. The invention of sustainable development by Barbara Ward, along with Rachel Carson the founder of the environmental movement, created an alliance of convenience between First World environmentalism and a Third World set on rapid industrialisation. The First Wave crashed in 1973 with the Yom Kippur War and decade-long energy crisis. Revived by a warming economy of the 1980s, environmentalism found a new, political champion in 1988: Margaret Thatcher. Four years later at the Rio Earth Summit, politics settled the science. One hundred and ninety-two nations agreed that mankind was causing global warming and carbon dioxide...

Global Warming: The Complete Briefing

Global Warming: The Complete Briefing
by John Houghton (Author)


John Houghton's market-leading textbook is now in full color and includes the latest IPCC findings, making it the definitive guide to climate change. Written for students across a wide range of disciplines, its simple, logical flow of ideas gives an invaluable grounding in the science and impacts of climate change and highlights the need for action on global warming. Is there evidence for climate changing due to human activities? How do we account for recent extremes of weather and climate? Can global electricity provision and transport ever be carbon free? Written by a leading figure at the forefront of action to confront humanity's most serious environmental problem, this undergraduate textbook comprehensively explores these and other issues, allowing students to think through the...

Climate Cover-Up: The Crusade to Deny Global Warming

Climate Cover-Up: The Crusade to Deny Global Warming
by James Hoggan (Author), Richard Littlemore (Contributor)


Talk of global warming is nearly inescapable these days — but there are some who believe the concept of climate change is an elaborate hoax. Despite the input of the world’s leading climate scientists, the urgings of politicians, and the outcry of many grassroots activists, many Americans continue to ignore the warning signs of severe climate shifts. How did this happen? Climate Cover-up seeks to answer this question, describing the pollsters and public faces who have crafted careful language to refute the findings of environmental scientists. Exploring the PR techniques, phony "think tanks," and funding used to pervert scientific fact, this book serves as a wake-up call to those who still wish to deny the inconvenient truth.

Windfall: The Booming Business of Global Warming

Windfall: The Booming Business of Global Warming
by McKenzie Funk (Author)


A fascinating investigation into how people around the globe are cashing in on a warming world

McKenzie Funk has spent the last six years reporting around the world on how we are preparing for a warmer planet. Funk shows us that the best way to understand the catastrophe of global warming is to see it through the eyes of those who see it most clearly—as a market opportunity.

Global warming’s physical impacts can be separated into three broad categories: melt, drought, and deluge. Funk travels to two dozen countries to profile entrepreneurial people who see in each of these forces a potential windfall.

The melt is a boon for newly arable, mineral-rich regions of the Arctic, such as Greenland—and for the surprising kings of the manmade snow trade,...

Climategate: A Veteran Meteorologist Exposes the Global Warming Scam

Climategate: A Veteran Meteorologist Exposes the Global Warming Scam
by Brian Sussman (Author)


Those now notorious intercepted emails documenting leading scientists conspiring to squelch global-warming skeptics and falsifying data proved exactly what Brian Sussman has been saying for years. Climategate is intended for anyone who has ever expressed skepticism about the clamorous environmentalist claims that the Earth is in peril because of mankind's appetite for carbon-based fuels. By tracing the origins of the current climate scare, Sussman guides the reader from the diabolical minds of Marx and Engles in the 1800s, to the global governance machinations of the United Nations today. Climategate is a call to action, warning Americans that their future is being undermined by a phony pseudo-science aimed at altering and dominating every aspect of life in the United States and the...

© 2014 BrightSurf.com