New study questions long-held theories of climate variability in the North Atlantic

A University of Miami (UM) Rosenstiel School of Marine and Atmospheric-led study challenges the prevailing wisdom by identifying the atmosphere as the driver of a decades-long climate variation known as the Atlantic Multi-decadal Oscillation (AMO).

The findings offer new insight on the causes and predictability of natural climate variations, which are known to cause wide-ranging global weather impacts, including increased rainfall, drought, and greater hurricane frequency in many parts of the Atlantic basin.

For decades, research on climate variations in the Atlantic has focused almost exclusively on the role of ocean circulation as the main driver, specifically the Atlantic Meridional Overturning Circulation, which carries warm water north in the upper layers of the ocean and cold water south in lower layers like a large conveyor belt.

“The idea of the ocean as the driver has been a powerful one.” said UM Rosenstiel School Professor Amy Clement, the lead author on the study. We used computer models in a new way to test this idea, and find that in fact there is a lot that can be explained without the ocean circulation.”

While the overall rise in average temperature of the Atlantic is caused by greenhouse gases, this study examines the fluctuations occurring within this human-related trend. Identifying the main driver of the AMO is critical to help predict the overall warming of the North Atlantic Ocean in coming decades from both natural and human-made climate change. Recent research suggests that an AMO warm phase has been in effect since the mid-1990s, which has caused changes in rainfall in the southeastern US, and resulted in twice as many tropical storms becoming hurricanes than during cool phases.

Using multiple climate models from around the world, Clement’s research team removed the ocean circulation from the analysis to reveal that variations in the Atlantic climate were generally the same. The AMO results in a horseshoe-shaped pattern of ocean surface temperatures in the North Atlantic Ocean that have been naturally occurring for the last 1000 years on timescales of 60-80 years. This new analysis shows that the pattern of the AMO can be accounted for by atmospheric circulation alone, without any role for the ocean circulation.

“These results force us to rethink our ability to predict decade-scale temperature fluctuations in the Atlantic and their associated impacts on land. It may be that many of the changes have limited predictability, which means that we should be prepared for a range of climate outcomes associated with global warming,” said Clement. More

The work was support by grants from the Department of Energy and the National Oceanographic and Atmospheric Administration.

Story Source:

The above post is reprinted from materials provided by University of Miami Rosenstiel School of Marine & Atmospheric Science. Note: Materials may be edited for content and length.

Journal Reference:

1. A. Clement, K. Bellomo, L. N. Murphy, M. A. Cane, T. Mauritsen, G. Radel, B. Stevens. The Atlantic Multidecadal Oscillation without a role for ocean circulation. Science, 2015; 350 (6258): 320 DOI: 10.1126/science.aab3980

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The 1.5 degrees global warming call from the Pacific, still possible

 

Amidst the recent release of scientific reports on climate change, the key message has been for urgent action to limit global warming, before time runs out.

The Intergovernmental Panel on Climate Change released their Synthesis Report on the 5th Assessment Report in October, the World Bank released the "Turn down the heat, confronting the new climate normal" report in November and the United Nations Environment Program released their "Bridging the 2014 Emission Gap Report" also in November.

According to the "Turn down the heat" report and an accompanying press release - climate change impacts such as extreme heat events may now be unavoidable because the Earth’s atmospheric system is locked into warming close to 1.5°C above pre-industrial levels by mid-century, and even very ambitious mitigation action taken today will not change this.

This does not mean, however, that long-term warming of 1.5°C is locked in, or that achievement of the 1.5°C warming limit, as called for by vulnerable countries like Pacific Islands, is no longer possible.

"What we see from the scientific literature is that it's clear that we can indeed hold warming below 2 degrees in this century probably with the most aggressive mitigation emission reduction options. We can limit peak warming close to 1.5 degrees and slowly reduce that to below 1.5 degrees by 2100," said Prof. Bill Hare of the Climate Analytics Group, Potsdam Institute.

"This is going to involve fairly major changes in policy settings now but this is what we are negotiating for, to have the emissions go down in the 2020's and if we can do that fast enough then its technically and economically feasible to bring warming back to 1.5 degrees by the end of the century."

"Those that are arguing it's not possible are expressing a political judgment, not a scientific judgment."

There will be climate change impacts experienced by several regions including the Pacific islands, before warming is reduced as limiting peak warming close to 1.5°C by mid century will still result in significant damage.

At the present levels of warming (about 0.8°C above preindustrial) the impacts of climate change are already being felt in many regions of the world. Continued damage is forecast to the coral reefs in the Pacific and other tropical oceans, there is the huge risk of damage to water supply resources in dry regions and substantial drops in crop yield in regions such as sub Saharan Africa.

"On top of that we'll also be experiencing quite major increase in extreme heat events even for 1.5 degrees warming so whatever happens we're going to have to go through some very severe changes," explains Professor Hare.

Here in Lima, Peru at the 20th Conference of the Parties to the United Nations Framework Convention on Climate Change (UNFCCC COP20), the Pacific islands are calling for a 1.5 degree limit to global warming by 2100. The next two weeks of climate negotiations continue the work being done by the Pacific islands as members of the Alliance of Small Islands States, lobbying for the 1.5 degree limit to global warming to be agreed upon in Paris next year.

The new climate treaty is to be agreed upon by the end of December in 2015 in Paris.

"Strengthening the long-term temperature goal to 1.5 degrees is of critical importance for us. Even at the current temperatures, our small low lying islands are being battered by king tides, salt water intrusion, coastal erosion, coral bleaching, ocean acidification, loss of species and habitats," said Ms. Ana Tiraa, Head of the Cook Islands delegation at the UNFCCC COP 20.

"These will only be exacerbated at higher temperatures, with due respect to other parties, the Cook Islands calls for ambition levels that are high enough to keep temperature rise below 1.5 degrees. Temperature rises above 1.5 degrees cannot be an option for low lying small islands if we have a hope of surviving."

According to Prof. Hare, at present there is confidence that with aggressive mitigation action warming can be held to below 2 degrees yet another decade of inaction will most likely lead to warming at 2 degrees or above. The message is clear that the time for action is now.

"It is still feasible to bring global warming to below 1.5 degrees by 2100 but whether or not the world politics and major economies will take enough action in the coming five to 20 years is in question. We are entitled to be skeptical given the inaction that has characterised the last decade as to whether that looks happening but it's not a scientific judgment or statement, the option is well and truly open to bring warming back to below 1.5 degrees. More

 

 

 

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Explaining Extreme Events of 2013

A report released today investigates the causes of a wide variety of extreme weather and climate events from around the world in 2013. Published by the Bulletin of the American Meteorological Society, "Explaining Extreme Events of 2013 from a Climate Perspective (link is external)" addresses the causes of 16 individual extreme events that occurred on four continents in 2013. NOAA scientists served as three of the four lead editors on the report.

Of the five heat waves studied in the report, human-caused climate change was found to have clearly increased the severity and likelihood of those events. On the other hand, for other events examined like droughts, heavy rain events, and storms, fingerprinting the influence of human activity was more challenging. Human influence on these kinds of events—primarily through the burning of fossil fuels—was sometimes evident, but often less clear, suggesting natural factors played a far more dominant role.

"This annual report contributes to a growing field of science which helps communities, businesses and nations alike understand the impacts of natural and human-caused climate change," said Thomas R. Karl, L.H.D., director of NOAA’s National Climatic Data Center. "The science remains challenging, but the environmental intelligence it yields to decision makers is invaluable and the demand is ever-growing."

Confidence in the role of climate change about any one event is increased when multiple groups using independent methods come to similar conclusions. For example, in this report, five independent research teams looked at specific factors related to the record heat in Australia in 2013. Each consistently found that human-caused climate change increased the likelihood and severity of that event. However, for the California drought, which was investigated by three teams from the United States, human factors were found not to have influenced the lack of rainfall. One team found evidence that atmospheric pressure patterns increased due to human causes, but the influence on the California drought remains uncertain.

When human influence for an event cannot be conclusively identified with the scientific tools available today, this means that if there is a human contribution, it cannot be distinguished from natural climate variability.

"There is great scientific value in having multiple studies analyze the same extreme event to determine the underlying factors that may have influenced it," said Stephanie C. Herring, PhD, lead editor for the report at NOAA’s National Climatic Data Center. "Results from this report not only add to our body of knowledge about what drives extreme events, but what the odds are of these events happening again—and to what severity."

The report was edited by Herring, along with Martin P. Hoerling, NOAA’s Earth System Research Laboratory; Thomas Peterson, NOAA’s National Climatic Data Center, and Peter A. Stott, UK Met Office Hadley Centre and written by 92 scientists from 14 countries. View the full report online (link is external).

Also, view the slides for the media briefing on the "Explaining Extreme Events of 2013 from a Climate Perspective" report. More

 

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The [US] House Committee Declares The IPCC Report Is Not Science

The Intergovernmental Panel on Climate Change (IPCC) report warned that more intense droughts and heat waves will cause famine and water shortages. But, don't worry! Yesterday, the GOP held a hearing to tell us the IPCC is, in fact, a global conspiracy to control our lives and "redistribute wealth among nations."

The hearing, titled "Examining the UN Intergovernmental Panel on Climate Change Process," was convened by the House Committee on Science, Space and Technology—the same folks who recently demonstrated their inability to grasp the idea that the world's climate varies across different regions and who informed us that warmer weather didn't bother the dinosaurs, so what's all the fuss about?

In principle, there's nothing wrong with assessing the methodology of such an important and influential report. But, in one of those quintessential moments of Washington double-think, Chairman Lamar Smith (R-TX)—who accuses the IPCC of creating data to serve a predetermined political agenda—summarized the hearing's conclusions a day before it even began. "The IPCC does not perform science itself and doesn't monitor the climate," Smith told a reporter, "but only reviews carefully selected scientific literature."

So, small wonder that Rep. Eddie Bernice Johnson (D-TX), the ranking Democrat on the committee, offered the opinion:

While the topic of today's hearing is a legitimate one, namely, how the IPCC process can be improved, I am concerned that the real objective of this hearing is to try to undercut the IPCC and to cast doubt on the validity of climate change research.

We aren't going to get very far if we spend our time continually revisiting a scientific debate that has already been settled. Nor will we get far if we continue a recent practice on this Committee of seeming to question the trustworthiness and integrity of this nation's scientific researchers.

Fair and Balanced

Another source of Johnson's skepticism might have been that three of the four expert witnesses testifying at the hearing either deny that humans are responsible for global warming or believe that the potential impact of climate change is grossly overstated.

The witnesses for the prosecution were:

(1) Roger Pielke,Sr.

Who is he?

Senior Research Scientist, Cooperative Institute for Research in Environmental Sciences, and Professor Emeritus of Atmospheric Science, Colorado State University

What's he known for?

Pielke says that carbon dioxide is responsible, at most, for about 28% of human-caused warming up to the present and he is among the most vocal skeptics of reports that the polar ice caps are melting and that sea levels are rising.

What did he say at the hearing?

The IPCC is "giving decision makers who face decisions at the regional and local level a false sense of certainty about the unfolding climate future."

(2) Richard Tol

Who is he?

A professor of economics at the University of Sussex

What's he known for?

He resigned his position with the IPCC team producing the working group's Summary for Policymakers, which he classified as "alarmist." Global warming creates benefits as well as harms, he believes, and in the short term, the benefits are especially pronounced. He's also expressed doubt that climate change will play any role in exacerbating conflicts.

Tol has been criticized by other scientists who have raised questions about his methodology and who have noted that he has a history of making contradictory statements. For instance, in a widely cited 2009 paper, he wrote of "considerable uncertainty about the economic impact of climate change … negative surprises are more likely than positive ones. … The policy implication is that reduction of greenhouse gas emissions should err on the ambitious side."

What did he say at the hearing?

"Academics who research climate change out of curiosity but find less than alarming things are ignored, unless they rise to prominence in which case they are harassed and smeared….The IPCC should therefore investigate the attitudes of its authors and their academic performance and make sure that, in the future, they are more representative of their peers."

(3) Daniel Botkin

Who is he?

Professor Emeritus, Department of Ecology, Evolution, and Marine Biology, University of California, Santa Barbara.

What's he known for?

He has long argued that life has had to deal with environmental change, especially climate change, since the beginning of its existence on Earth—and that we underestimate the ability of species, including humans, to find ways to adapt to the problem.

Botkin wrote a controversial editorial for the Wall Street Journal (Oct 17, 2007) arguing that global warming will not have much impact on life on Earth, and noted that: "the reality is that almost none of the millions of species have disappeared during the past 2.5 million years — with all of its various warming and cooling periods."

The editorial prompted several responses from within the scientific community, including this:

For the past 2.5 million years the climate has oscillated between interglacials which were (at most) a little warmer than today and glacials which were considerably colder than today. There is no precedent in the past 2.5 million years for so much warming so fast. The ecosystem has had 2.5 million years to adapt to glacial-interglacial swings, but we are asking it to adapt to a completely new climate in just a few centuries. The past is not a very good analog for the future in this case. And anyway, the human species can suffer quite a bit before we start talking extinction.

What did he say at the hearing?

"I want to state up front that we have been living through a warming trend driven by a variety of influences. However, it is my view that this is not unusual, and contrary to the characterizations by the IPCC….these environmental changes are not apocalyptic nor irreversible…..Yes, we have been living through a warming trend, no doubt about that. The rate of change we are experiencing is also not unprecedented, and the "mystery" of the warming "plateau" simply indicates the inherent complexity of our global biosphere. Change is normal, life on Earth is inherently risky; it always has been."

The Q & A

The lone witness for the defense was Michael Oppenheimer, the Albert G. Milbank Professor of Geosciences and International Affairs at Princeton University. He was selected by the Democrats, "because he's one of the foremost experts in the world and has been involved with the IPCC," a spokesperson for the Democratic contingent of the committee told Motherboard reporter Jason Koebler.

Koebler describes how things went down at the hearing after the experts presented their statements:

For two hours, climate change deniers interrupted, berated, and cut off Oppenheimer, while the other three other witnesses fielded softball questions from conservative lawmakers and dodged tougher ones from Democratic ones.

In fact, at one point, Rep. Larry Buchson (R-Ind.), who, seconds before had interrupted Oppenheimer and said he wasn't interested in hearing his views, wanted to "apologize on behalf of Congress" to Pielke for the aforementioned "juvenile and insulting questions trying to disparage the credibility" of witnesses who didn't take climate change seriously…..

Dana Rohrabacher [R-CA] pulled out the air quotes when he said "global warming," and took offense to Oppenheimer not being able to "capsulize" all the reasons why he believes that climate change is a big deal in 10 seconds. Smith suggested that the "only thing we know about [climate change models] is that they will be wrong" and suggested that "even if the US was completely eliminated, it's not going to have any discernible impact on global temperatures in the near or far future."

Paul Broun [R-GA] and Buchson noted their belief in the "scientific process" and suggested that they knew more about it because they are doctors (Broun is a dentist; Buchson is a surgeon).

So predictable, and such a waste of time. As I noted earlier, in principle, there is nothing wrong with assessing the methodology of such an important and influential report. But there are far better ways to do it than this. More

 

© 2014