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


Ocean pipes 'not cool,' would end up warming climate
To combat global climate change caused by greenhouse gases, alternative energy sources and other types of environmental recourse actions are needed. There are a variety of proposals that involve using vertical ocean pipes to move seawater to the surface from the depths in order to reap different potential climate benefits.

Massive amounts of fresh water, glacial melt pouring into Gulf of Alaska
Incessant mountain rain, snow and melting glaciers in a comparatively small region of land that hugs the southern Alaska coast and empties fresh water into the Gulf of Alaska would create the sixth largest coastal river in the world if it emerged as a single stream, a recent study shows.

Hidden benefits of electric vehicles revealed
Electric vehicles are cool, research shows. Literally. A study in this week's Scientific Reports by researchers at Michigan State University (MSU) and in China add more fuel to the already hot debate about whether electric vehicles are more environmentally friendly than conventional vehicles by uncovering two hidden benefits.

Global warming brings more snow to Antarctica
"Warmer air transports more moisture and hence produces more precipitation - in cold Antarctica this takes the form of snowfall," lead author Katja Frieler from the Potsdam Institute for Climate Impact Research (PIK) explains.

Summer storm weakening leads to more persistent heat extremes
This is shown in a study to be published in the renowned journal Science by a team of researchers from the Potsdam Institute for Climate Impact Research. They link the findings to changes in the Arctic caused by man-made global warming.

Blue blood on ice -- how an Antarctic octopus survives the cold
An Antarctic octopus that lives in ice-cold water uses an unique strategy to transport oxygen in its blood, according to research published in Frontiers in Zoology.

Methane in Arctic lake traced to groundwater from seasonal thawing
Global warming may ramp up the flow of methane from groundwater into Arctic lakes, allowing more of the potent greenhouse gas to bubble out into the atmosphere, according to a new study led by researchers at UC Santa Cruz.

Small eddies produce global effects on climate change
The increasing strength of winds over the Southern Ocean has extended its ability to absorb carbon dioxide, effectively delaying the impacts of global warming.

New detector sniffs out origins of methane
Methane is a potent greenhouse gas, second only to carbon dioxide in its capacity to trap heat in Earth's atmosphere for a long time.

Space technology investigates large-scale changes to Africa's climate
An international research team led by the University of Leicester has mapped the entire African continent south of the Sahara for geographical changes - and has discovered that many areas receive drastically different amounts of rainfall today compared to just ten years ago.
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

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

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 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...

The Great Global Warming Blunder: How Mother Nature Fooled the Worldâs 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 & Deniers; A Geoscientist looks at the Science of Climate Change

Global Warming: Alarmists, Skeptics & Deniers; A Geoscientist looks at the Science of Climate Change
by Moonshine Cove Publishing, LLC


“The author makes it very clear that a changing climate is not unusual. It is in fact the norm -- although change is often so slow that humans cannot detect it directly.  But historical geologists know how to display the evidence to the public. This may be the single most important contribution of this well-written and fact-filled book.”—Dr. S. Fred Singer, Chairman Science & Environmental Policy Project

“Global Warming: Alarmists, Skeptics and Deniers is a refreshing read on a topic of great societal importance; refreshing because, unlike many books published on this subject, the authors of this work evaluate key predictions and controversies of the global warming debate using logic and science.  Most readers will appreciate the book’s arrangement.  Each chapter...

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...

Unstoppable Global Warming: Every 1,500 Years, Updated and Expanded Edition

Unstoppable Global Warming: Every 1,500 Years, Updated and Expanded Edition
by S. Fred Singer (Author), Dennis T. Avery (Author)


Singer and Avery present—in popular language supported by in-depth scientific evidence—the compelling concept that global temperatures have been rising mostly or entirely because of a natural cycle. Using historic data from two millennia of recorded history combined with the natural physical records found in ice cores, seabed sediment, cave stalagmites, and tree rings, Unstoppable Global Warming argues that the 1,500 year solar-driven cycle that has always controlled the earth's climate remains the driving force in the current warming trend. Trillions of dollars spent on reducing fossil fuel use would have no effect on today's rising temperatures. The public policy key, Singer and Avery propose, is adaptation, not fruitless attempts at prevention. Further, they offer convincing...

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.

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...

© 2015 BrightSurf.com