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


What would it take to limit climate change to 1.5°C?
Limiting temperature rise by 2100 to less than 1.5°C is feasible, at least from a purely technological standpoint, according to the study published in the journal Nature Climate Change by researchers at the International Institute for Applied Systems Analysis (IIASA), the Potsdam Institute for Climate Impact Research (PIK), and others.

Cold-blooded animals find it hard to adjust to global warming
Cold-blooded and other animals that are unable to regulate their internal temperature may have a hard time tolerating global warming, according to an analysis by biologists from the University of California, Berkeley, and San Francisco State University.

Climate change could cause cold-blooded animals' thermal tolerance to shrink
Cold-blooded animals can tolerate body temperatures only a few degrees above their normal high temperatures before they overheat, which could be a problem as the planet itself warms, according to San Francisco State University researchers.

Diverse soil communities can help offset impacts of global warming
Maintaining a healthy and diverse soil community can buffer natural ecosystems against the damaging impacts of global warming, according to a new Yale-led study.

Stanford scientists discover how microbes acquire electricity in making methane
Stanford University scientists have solved a long-standing mystery about methanogens, unique microorganisms that transform electricity and carbon dioxide into methane.

Climate scientists find elusive tropospheric hot spot
Researchers have published results in Environmental Research Letters confirming strong warming in the upper troposphere, known colloquially as the tropospheric hotspot. The hot has been long expected as part of global warming theory and appears in many global climate models.

Carbon emissions from peatlands may be less than expected
Duke University scientists have discovered a previously unknown dual mechanism that slows peat decay and may help reduce carbon dioxide emissions from peatlands during times of drought.

Solution to corrosive ocean mystery reveals future climate
Around 55 million years ago, an abrupt global warming event triggered a highly corrosive deep-water current to flow through the North Atlantic Ocean. The origin of this corrosive water has puzzled scientists for a decade.

Solving corrosive ocean mystery reveals future climate
Around 55 million years ago, an abrupt global warming event triggered a highly corrosive deep-water current through the North Atlantic Ocean.

Dissecting the ocean's unseen waves to learn where the heat, energy and nutrients go
Beyond the pounding surf loved by novelists and beachgoers alike, the ocean contains rolling internal waves beneath the surface that displace massive amounts of water and push heat and vital nutrients up from the deep ocean.
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...

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 really using...

This Changes Everything: Capitalism vs. The Climate

This Changes Everything: Capitalism vs. The Climate
by Naomi Klein (Author)


The most important book yet from the author of the international bestseller The Shock Doctrine, a brilliant explanation of why the climate crisis challenges us to abandon the core “free market” ideology of our time, restructure the global economy, and remake our political systems.

In short, either we embrace radical change ourselves or radical changes will be visited upon our physical world. The status quo is no longer an option.

In This Changes Everything Naomi Klein argues that climate change isn’t just another issue to be neatly filed between taxes and health care. It’s an alarm that calls us to fix an economic system that is already failing us in many ways. Klein meticulously builds the case for how massively reducing our greenhouse emissions is our best chance...

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...

Global Warming-Alarmists, Skeptics and Deniers: A Geoscientist Looks at the Science of Climate Change

Global Warming-Alarmists, Skeptics and Deniers: A Geoscientist Looks at the Science of Climate Change
by G. Dedrick Robinson (Author), Gene D. Robinson III (Author)


Global Warming-Alarmists, Skeptics & Deniers: A Geoscientist looks at the Science of Climate Change, brings a unique geological perspective to this politically charged issue, a perspective that has been ignored far too long. Written by a father-son team of geoscientist and attorney, it is the concise guide to the global warming controversy that has been long needed. As a university professor and research geologist for thirty years, Dr. Robinson knows that geological science is essential for placing the global warming controversy in proper prospective. One cannot hope to understand how humans might be causing climate change without an understanding of the magnitude and speed natural processed are capable of when it comes to climate change. Earth history is the only yardstick we have to...

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, the Israelis....

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

Climate Change: The Facts

Climate Change: The Facts
by J.Abbot (Author), J.S. Armstrong (Author), A.Bolt (Author), R.Carter (Author), R.Darwall (Author), J.Delingpole (Author), C.Essex (Author), S.Franks (Author), K.Green (Author), D.Laframboise (Author), N.Lawson (Author), B.Lewin (Author), R.Lindzen (Author), J.Marohasy (Author), R.McKitrick (Author), P.Michaels (Author), A.Moran (Author), J.Nova (Author), G.Paltridge (Author), I.Plimer (Author), W.Soon (Author), M.Steyn (Author), A.Watts (Author), Alan Moran (Editor)


Tirelessly promoted by princes, presidents, actors and activists, "climate change" has become a dominant theme of global politics. But what's really going on as the "pause" in global warming prepares to enter its third decade? In this new anthology, leading scientists and commentators from the United States, the United Kingdom, Canada and Australia consider the climate from every angle - the science, the policy and the politics.

The Sixth Extinction: An Unnatural History

The Sixth Extinction: An Unnatural History
by Elizabeth Kolbert (Author)


A NEW YORK TIMES BESTSELLER
A NATIONAL BOOK CRITICS CIRCLE AWARD FINALISTOver the last half-billion years, there have been Five mass extinctions, when the diversity of life on earth suddenly and dramatically contracted. Scientists around the world are currently monitoring the sixth extinction, predicted to be the most devastating extinction event since the asteroid impact that wiped out the dinosaurs. This time around, the cataclysm is us. In prose that is at once frank, entertaining, and deeply informed, New Yorker writer Elizabeth Kolbert tells us why and how human beings have altered life on the planet in a way no species has before. Interweaving research in half a dozen disciplines, descriptions of the fascinating species that have already been lost, and the history of extinction...

The Politically Incorrect Guide to Global Warming (and Environmentalism)

The Politically Incorrect Guide to Global Warming (and Environmentalism)
by Christopher C. Horner (Author)


Global warming":
the Left's last best chance to gain a stranglehold on our political system and economy

For decades, environmentalism has been the Left's best excuse for increasing government control over our actions in ways both large and small. It's for Mother Earth! It's for the children! It's for the whales! But until now, the doomsday-scenario environmental scares they've trumped up haven't been large enough to justify the lifestyle restrictions they want to impose. With global warming, however, greenhouse gasbags can argue that auto emissions in Ohio threaten people in Paris, and that only "global governance" (Jacques Chirac's words) can tackle such problems.

Now, in The Politically Incorrect Guide(tm) to Global Warming and Environmentalism, Christopher C. Horner...

© 2015 BrightSurf.com