Sensitivity of carbon cycle to tropical temperature variations has doubled

Sensitivity of carbon cycle to tropical temperature variations has doubled
Jan 26, 2014 
          

The tropical carbon cycle has become twice as sensitive to temperature variations over the past 50 years, new research has revealed.

The research shows that a one degree rise in tropical temperature leads to around two billion extra tonnes of carbon being released per year into the atmosphere from tropical ecosystems, compared with the same tropical warming in the 1960s and 1970s.

Professor Pierre Friedlingstein and Professor Peter Cox, from the University of Exeter, collaborated with an international team of researchers from China, Germany, France and the USA, to produce the new study, which is published in the leading academic journal Nature.

Existing Earth System Model simulations indicate that the ability of tropical land ecosystems to store carbon will decline over the 21st century. However, these models are unable to capture the increase in the sensitivity of carbon dioxide to tropical temperatures that is reported in this new study.

Research published last year by Professors Cox and Friedlingstein showed that these variations in atmospheric carbon dioxide can reveal the sensitivity of tropical ecosystems to future climate change.
Taken together, these studies suggest that the sensitivity of tropical ecosystems to climate change has increased substantially in recent decades.

Professor Cox, from the College of Engineering, Mathematics and Physical Sciences said "The year-to-year variation in carbon dioxide concentration is a very useful way to monitor how tropical ecosystems are responding to climate.

"The increase in carbon dioxide variability in the last few decades suggests that tropical ecosystems have become more vulnerable to warming".

Professor Friedlingstein, who is an expert in global carbon cycle studies added: "Current land carbon cycle models do not show this increase over the last 50 years, perhaps because these models underestimate emerging drought effects on tropical ecosystems".

The lead author of the study, Xuhui Wang of Peking University, added: "This enhancement is very unlikely to have resulted from chance, and may provide a new perspective on a possible shift in the terrestrial carbon cycle over the past five decades".

Explore further: Lungs of the planet reveal their true sensitivity to global warming

More information: A two-fold increase of carbon cycle sensitivity to tropical temperature variations, DOI: 10.1038/nature12915

Journal reference: Nature 

Picture of how our climate is affected by greenhouse gases is a 'cloudy' one -- ScienceDaily

Picture of how our climate is affected by greenhouse gases is a 'cloudy' one -- ScienceDaily

Date:

January 26, 2014

Source:

Hebrew University of Jerusalem

Summary:

The warming effect of human-induced greenhouse gases is a given, but to what extent can we predict its future influence? That is an issue on which science is making progress, but the answers are still far from exact, say researchers.

 

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Recent studies have revealed a highly complicated picture of aerosol-cloud interactions.

Credit: © Maksim Shebeko / Fotolia

[Click to enlarge image]

Recent studies have revealed a highly complicated picture of aerosol-cloud interactions.Credit: © Maksim Shebeko / Fotolia

 

The warming effect of human-induced greenhouse gases is a given, but to what extent can we predict its future influence? That is an issue on which science is making progress, but the answers are still far from exact, say researchers from the Hebrew University of Jerusalem, the US and Australia who have studied the issue and whose work which has just appeared in the journal Science.

Indeed, one could say that the picture is a "cloudy" one, since the determination of the greenhouse gas effect involves multifaceted interactions with cloud cover.

To some extent, aerosols -- particles that float in the air caused by dust or pollution, including greenhouse gases -- counteract part of the harming effects of climate warming by increasing the amount of sunlight reflected from clouds back into space. However, the ways in which these aerosols affect climate through their interaction with clouds are complex and incompletely captured by climate models, say the researchers. As a result, the radiative forcing (that is, the disturbance to Earth's "energy budget" from the sun) caused by human activities is highly uncertain, making it difficult to predict the extent of global warming.

And while advances have led to a more detailed understanding of aerosol-cloud interactions and their effects on climate, further progress is hampered by limited observational capabilities and coarse climate models, says Prof. Daniel Rosenfeld of the Fredy and Nadine Herrmann Institute of Earth Sciences at the Hebrew University of Jerusalem, author of the article in Science. Rosenfeld wrote this article in cooperation with Dr. Steven Sherwood of the University of New South Wales, Sydney, Dr. Robert Wood of the University of Washington, Seattle, and Dr. Leo Donner of the US National Oceanic and Atmospheric Administration. .

Their recent studies have revealed a much more complicated picture of aerosol-cloud interactions than considered previously. Depending on the meteorological circumstances, aerosols can have dramatic effects of either increasing or decreasing the cloud sun-deflecting effect, the researchers say. Furthermore, little is known about the unperturbed aerosol level that existed in the preindustrial era. This reference level is very important for estimating the radiative forcing from aerosols.

Also needing further clarification is the response of the cloud cover and organization to the loss of water by rainfall. Understanding of the formation of ice and its interactions with liquid droplets is even more limited, mainly due to poor ability to measure the ice-nucleating activity of aerosols and the subsequent ice-forming processes in clouds.

Explicit computer simulations of these processes even at the scale of a whole cloud or multi-cloud system, let alone that of the planet, require hundreds of hours on the most powerful computers available. Therefore, a sufficiently accurate simulation of these processes at a global scale is still impractical.
Recently, however, researchers have been able to create groundbreaking simulations in which models were formulated presenting simplified schemes of cloud-aerosol interactions, This approach offers the potential for model runs that resolve clouds on a global scale for time scales up to several years, but climate simulations on a scale of a century are still not feasible. The model is also too coarse to resolve many of the fundamental aerosol-cloud processes at the scales on which they actually occur. Improved observational tests are essential for validating the results of simulations and ensuring that modeling developments are on the right track, say the researchers.

While it is unfortunate that further progress on understanding aerosol-cloud interactions and their effects on climate is limited by inadequate observational tools and models, achieving the required improvement in observations and simulations is within technological reach, the researchers emphasize, provided that the financial resources are invested. The level of effort, they say, should match the socioeconomic importance of what the results could provide: lower uncertainty in measuring human-made climate forcing and better understanding and predictions of future impacts of aerosols on our weather and climate.

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Story Source:
The above story is based on materials provided by Hebrew University of Jerusalem. Note: Materials may be edited for content and length.

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Journal Reference:

1. D. Rosenfeld, S. Sherwood, R. Wood, L. Donner. Climate Effects of Aerosol-Cloud Interactions. Science, 2014; 343 (6169): 379 DOI: 10.1126/science.1247490

Global Warming Alarmists Caught Doctoring '97-Percent Consensus' Claims

                   
Peter Ferrara

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Global warming alarmists and their allies in the liberal media have been caught doctoring the results of a widely cited paper asserting there is a 97-percent scientific consensus regarding human-caused global warming. After taking a closer look at the paper, investigative journalists report the authors’ claims of a 97-pecent consensus relied on the authors misclassifying the papers of some of the world’s most prominent global warming skeptics. At the same time, the authors deliberately presented a meaningless survey question so they could twist the responses to fit their own preconceived global warming alarmism.

Global warming alarmist John Cook, founder of the misleadingly named blog site Skeptical Science, published a paper with several other global warming alarmists claiming they reviewed nearly 12,000 abstracts of studies published in the peer-reviewed climate literature. Cook reported that he and his colleagues found that 97 percent of the papers that expressed a position on human-caused global warming “endorsed the consensus position that humans are causing global warming.”

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As is the case with other ‘surveys’ alleging an overwhelming scientific consensus on global warming, the question surveyed had absolutely nothing to do with the issues of contention between global warming alarmists and global warming skeptics. The question Cook and his alarmist colleagues surveyed was simply whether humans have caused some global warming. The question is meaningless regarding the global warming debate because most skeptics as well as most alarmists believe humans have caused some global warming. The issue of contention dividing alarmists and skeptics is whether humans are causing global warming of such negative severity as to constitute a crisis demanding concerted action.

Either through idiocy, ignorance, or both, global warming alarmists and the liberal media have been reporting that the Cook study shows a 97 percent consensus that humans are causing a global warming crisis. However, that was clearly not the question surveyed.

Investigative journalists at Popular Technology looked into precisely which papers were classified within Cook’s asserted 97 percent. The investigative journalists found Cook and his colleagues strikingly classified papers by such prominent, vigorous skeptics as Willie Soon, Craig Idso, Nicola Scafetta, Nir Shaviv, Nils-Axel Morner and Alan Carlin as supporting the 97-percent consensus.
Cook and his colleagues, for example, classified a peer-reviewed paper by scientist Craig Idso as explicitly supporting the ‘consensus’ position on global warming “without minimizing” the asserted severity of global warming. When Popular Technology asked Idso whether this was an accurate characterization of his paper, Idso responded, “That is not an accurate representation of my paper.

The papers examined how the rise in atmospheric CO2 could be inducing a phase advance in the spring portion of the atmosphere’s seasonal CO2 cycle. Other literature had previously claimed a measured advance was due to rising temperatures, but we showed that it was quite likely the rise in atmospheric CO2 itself was responsible for the lion’s share of the change. It would be incorrect to claim that our paper was an endorsement of CO2-induced global warming.”

When Popular Technology asked physicist Nicola Scafetta whether Cook and his colleagues accurately classified one of his peer-reviewed papers as supporting the ‘consensus’ position, Scafetta similarly criticized the Skeptical Science classification.

“Cook et al. (2013) is based on a straw man argument because it does not correctly define the IPCC AGW theory, which is NOT that human emissions have contributed 50%+ of the global warming since 1900 but that almost 90-100% of the observed global warming was induced by human emission,” Scafetta responded. “What my papers say is that the IPCC [United Nations Intergovernmental Panel on Climate Change] view is erroneous because about 40-70% of the global warming observed from 1900 to 2000 was induced by the sun.”

“What it is observed right now is utter dishonesty by the IPCC advocates. … They are gradually engaging into a metamorphosis process to save face. … And in this way they will get the credit that they do not merit, and continue in defaming critics like me that actually demonstrated such a fact since 2005/2006,” Scafetta added.

Astrophysicist Nir Shaviv similarly objected to Cook and colleagues claiming he explicitly supported the ‘consensus’ position about human-induced global warming. Asked if Cook and colleagues accurately represented his paper, Shaviv responded, “Nope… it is not an accurate representation. The paper shows that if cosmic rays are included in empirical climate sensitivity analyses, then one finds that different time scales consistently give a low climate sensitivity. i.e., it supports the idea that cosmic rays affect the climate and that climate sensitivity is low. This means that part of the 20th century [warming] should be attributed to the increased solar activity and that 21st century warming under a business as usual scenario should be low (about 1°C).”

“I couldn’t write these things more explicitly in the paper because of the refereeing, however, you don’t have to be a genius to reach these conclusions from the paper,” Shaviv added.

To manufacture their misleading asserted consensus, Cook and his colleagues also misclassified various papers as taking “no position” on human-caused global warming. When Cook and his colleagues determined a paper took no position on the issue, they simply pretended, for the purpose of their 97-percent claim, that the paper did not exist.

Morner, a sea level scientist, told Popular Technology that Cook classifying one of his papers as “no position” was “Certainly not correct and certainly misleading. The paper is strongly against AGW [anthropogenic global warming], and documents its absence in the sea level observational facts. Also, it invalidates the mode of sea level handling by the IPCC.”

Soon, an astrophysicist, similarly objected to Cook classifying his paper as “no position.”

“I am sure that this rating of no position on AGW by CO2 is nowhere accurate nor correct,” said Soon.

“I hope my scientific views and conclusions are clear to anyone that will spend time reading our papers. Cook et al. (2013) is not the study to read if you want to find out about what we say and conclude in our own scientific works,” Soon emphasized.

Viewing the Cook paper in the best possible light, Cook and colleagues can perhaps claim a small amount of wiggle room in their classifications because the explicit wording of the question they analyzed is simply whether humans have caused some global warming. By restricting the question to such a minimalist, largely irrelevant question in the global warming debate and then demanding an explicit, unsolicited refutation of the assertion in order to classify a paper as a ‘consensus’ contrarian, Cook and colleagues misleadingly induce people to believe 97 percent of publishing scientists believe in a global warming crisis when that is simply not the case.

Misleading the public about consensus opinion regarding global warming, of course, is precisely what the Cook paper sought to accomplish. This is a tried and true ruse perfected by global warming alarmists. Global warming alarmists use their own biased, subjective judgment to misclassify published papers according to criteria that is largely irrelevant to the central issues in the global warming debate. Then, by carefully parsing the language of their survey questions and their published results, the alarmists encourage the media and fellow global warming alarmists to cite these biased, subjective, totally irrelevant surveys as conclusive evidence for the lie that nearly all scientists believe humans are creating a global warming crisis.

These biased, misleading, and totally irrelevant “surveys” form the best “evidence” global warming alarmists can muster in the global warming debate. And this truly shows how embarrassingly feeble their alarmist theory really is.

Climate change needs a new kind of scientist

Jan 17 2014

BY Amy Duchelle

Scientific discoveries of recent decades have generated a wealth of knowledge on forests and climate change spanning many different sectors and disciplines. Sustainable development, poverty eradication, the rights of indigenous and local communities to land and resources, conservation of biodiversity, governance, water management, pollution (and all the policies and economic factors related to these sectors) are just some of the issues that scientists studying the relationship between forests climate change must consider.

Such knowledge generation has also laid the foundation for a broader mission to assist in developing integrated solutions. This is not something that we, as climate scientists, have been traditionally trained to do.

It’s clear that developing integrated solutions to such complex problems will require a new kind of climate scientist. A scientist who can think across biophysical and social disciplines. A scientist who can work across scales to engage all members of society in their research. A scientist who can understand the policy implications of their work.

One group that seems particularly enthusiastic to take on such a role is young researchers. In this article, I’ll go through a few examples where young researchers have led the “out of the box” thinking needed to tackle climate change problems.

Interdisciplinary science is at the heart of CIFOR’s Global Comparative Study on REDD+, which aims to inform policy makers, practitioners and donors about what works in reducing emissions from deforestation and forest degradation, and enhancement of forest carbon stocks (REDD+) in tropical countries.

In this study, a diverse group of foresters, biologists, sociologists, economists, political scientists, and anthropologists works together to understand how REDD+ can be implemented effectively, efficiently, equitably, and promote both social and environmental co-benefits.

I help coordinate a component of the study that focuses on measuring the impacts of subnational REDD+ initiatives. Through this part of the study, we have collected data in 170 villages with over 4,000 families in 6 countries: Brazil, Peru, Cameroon, Tanzania, Vietnam and Indonesia.
From 2010 to 2012, we hired nearly 80 undergraduate, Masters and PhD students in Latin America to collect baseline data on livelihoods and land-use at multiple sites across the Amazon. These young scientists have been critical in helping us share project knowledge in different ways.

KNOWLEDGE SHARING
As I was finishing my PhD six years ago, I joined forces with bunch of graduate students who were thinking about how, within our confined academic research environment, we could share knowledge in different ways.

The “knowledge exchange pyramid” (Fig 1) outlines how graduate students can exchange knowledge with local stakeholders during research.

There are three levels of knowledge exchange: (1) information sharing; (2) skill building; and (3) knowledge generation. The black circle represents the researchers while the white circle represents local stakeholders — communities, practitioners, policymakers.

Duchelle, A.E, K. Biedenweg, C. Lucas, A. Virapongse, J. Radachowsky, D. Wojcik, M. Londres, W.L. Bartels, D. Alvira, K.A. Kainer. 2009. Graduate students and knowledge exchange with local stakeholders: Possibilities and preparation. Biotropica 41(5): 578-585.

At the base of the pyramid (the simplest form of knowledge exchange) is information sharing – a primarily one-way transmission of ideas to stakeholders using presentations, brochures and posters. Our experience showed that these tools are particularly appropriate when time is limited, specific facts need to be shared, and information is not controversial.

If your goal is to change attitudes, you need to ensure that stakeholders are given a more active role in interpreting information either through community forums, presentations allowing discussion time, and short workshops.

An example of information sharing is returning research results to local stakeholders. One year after the teams collected baseline data for the Global Comparative Study on REDD+, we went back to all of the research sites and shared the results with the local communities and with the organizations (NGOs and governments) that implement the REDD+ activities.

While many researchers do go back to the places where they collected their data to share results, it has bothered me for years when you go to communities where you know there have been multiple research groups and they say to you, ‘you guys are the first group that come back with the information’.

While many researchers do go back to the places where they collected their data to share results, it has bothered me for years when you go to communities where you know there have been multiple research groups and they say to you, ‘you guys are the first group that come back with the information’.

Sharing results with local stakeholders is an incredibly important learning process and it makes good scientific sense. It allows community members to interpret the information and verify survey data before final analysis. We have found that when a community says ‘that doesn’t make sense, why would it be that way?’, it helps us rethink our interpretation of the data. All it takes is some time, some creativity, and a bit of money.

In the Global Comparative Study on REDD+, I envisaged us returning the results in a pretty conventional way. What blew me away was the innovation of our young researchers – they used art, games and even theatre to make the science interesting and relevant to local communities.
In the second part of the pyramid (slightly more complex knowledge exchange) is skill building, which encourages stakeholders to use knowledge to develop new skills. This is often a response to local demands for skills such as data collection and analysis, grant writing, or manuscript preparation.
While conducting research in Ucayali, Peru forest communities requested training in Global Positioning Systems (GPS) to help them locate and record specific trees in timber harvest areas required by their forest management plans. They also wanted to learn how to measure timber so they could determine a reasonable purchase price (and ensure they weren’t being swindled when it came time to sell the tree trunks or boards).

Skill building activities require more time, resources, and preparation than information sharing but can be incredibly important for building trust with communities. They can also be fun (friendly soccer games are a common feature of fieldwork in Latin America!)
At the highest level of the pyramid is knowledge generation, which includes communities, practitioners or policy makers as partners in different aspects of the research process (one example is “action research”). Together with the graduate researcher, they can create the research questions, implement the research, and analyze and disseminate the results.
While this is the most innovative type of knowledge exchange, it is also the hardest for young researchers to get involved in. Graduate students and their research partners will need to invest a lot of time and energy as well as obtain institutional support.

I know a Brazilian researcher who, before and during her Masters in The University of Florida’s Tropical Conservation and Development Program, developed long-term action research on the ecology of locally important tree species with one remote community in the Amazon estuary. She involved community members in all steps of the research process from setting research priorities, collecting data and training.

After assessing the research findings, community members took several actions. They more than doubled the number of local volunteers collecting data (and diversified to include youth, women, and community leaders), they presented research findings at community meetings and they shared those findings with nearby communities struggling to improve their livelihoods in a sustainable way.
Engaging local stakeholders in research is possible at any level. Young researchers are the ones who can help us think of new and innovative ways to do this.

MAKE USE OF THIS INFORMATION
If you are in academia, encourage your students to embark on this kind of knowledge exchange in their research. Plug them into your networks and create courses to help broaden their skill sets.
If you are a practitioner, welcome students and young researchers into your work. Be willing to develop research with them, be willing to learn from students and help them become better professionals.

If you are a donor, support the research that shows real and genuine knowledge exchange with relevant stakeholders.

If you are a student or young researcher, recognize the very unique moment that you are in right now in your career and expand your skill set. Some of the conventional academic pressures are less placed on you at early stages of your career, so use the opportunity you have now to engage and innovate.

This article was first published on ForestsClimateChange.org

What Happens When You Can't Get an Abortion?

—By Kevin Drum

| Thu Jun. 13, 2013 7:59 AM GMT

What happens to women who want abortions but can't get them? Abortion clinics all have "gestational deadlines" and will turn away women who are further into pregnancy than their rules allow, and this gave Diane Greene Foster, a professor of obstetrics and gynecology at UC San Francisco, an idea for a study. Instead of comparing women who have abortions to women who elect to carry their pregnancy to term, she compared a group of women who all wanted to have an abortion but didn't all get one:



When she looked at more objective measures of mental health over time — rates of depression and anxiety — she also found no correlation between having an abortion and increased symptoms....Turnaways did [] suffer from higher levels of anxiety, but six months out, there were no appreciable differences between the two groups.
Where the turnaways had more significant negative outcomes was in their physical health and economic stability....Women in the turnaway group suffered more ill effects, including higher rates of hypertension and chronic pelvic pain....Even “later abortions are significantly safer than childbirth,” she says.
....Economically, the results are even more striking. Adjusting for any previous differences between the two groups, women denied abortion were three times as likely to end up below the federal poverty line two years later. Having a child is expensive, and many mothers have trouble holding down a job while caring for an infant. Had the turnaways not had access to public assistance for women with newborns, Foster says, they would have experienced greater hardship.

The whole story is worth a read. In the long run, women who want abortions but don't get them adjust to their new lives. They aren't unhappy at becoming mothers. But there's not much question that their lives suffer, and as more and more states put more and more roadblocks in the way of abortion providers, that suffering will increase—with no mitigation from increased social services, since the red states that oppose abortion also generally don't think highly of providing much in the way of services to mothers in poverty.

Future solar cells may be made of wood

Future solar cells may be made of wood

Jan 23, 2014 by Lisa Zyga

       

(a) A schematic of the hierarchical structure of a tree in which each structure is broken down to the level of the elementary fibrils. (b) Regular paper with microfibers has a microporous structure that causes light scattering. (c) The new …more

(Phys.org) —A new kind of paper that is made of wood fibers yet is 96% transparent could be a revolutionary material for next-generation solar cells. Coming from plants, the paper is inexpensive and more environmentally friendly than the plastic substrates often used in solar cells. However, its most important advantage is that it overcomes the tradeoff between optical transparency and optical haze that burdens most materials.

A team of researchers from the University of Maryland, the South China University of Technology, and the University of Nebraska-Lincoln, have published a paper on the new material in a recent issue of Nano Letters.

As the researchers explain, solar cell performance benefits when materials possess both a high optical transparency (to allow for good light transmission) and a high optical haze (to increase the scattering and therefore the absorption of the transmitted light within the material). But so far, materials with high transparency values (of about 90%) have very low optical haze values (of less than 20%).

The new wood-based paper has an ultrahigh transparency of 96% and ultrahigh optical haze of 60%, which is the highest optical haze value reported among transparent substrates.
The main reason for this good performance in both areas is that the paper has a nanoporous rather than microporous structure. Regular paper is made of wood fibers and has low optical transparency due to the microcavities that exist within the porous structure that cause light scattering. In the new paper, these micropores are eliminated in order to improve the optical transparency. To do this, the researchers used a treatment called TEMPO to weaken the hydrogen bonds between the microfibers that make up the wood fibers, which causes the wood fibers to swell up and collapse into a dense, tightly packed structure containing nanopores rather than micropores.

        

Optical transmission haze versus transmittance for different substrates at 550 nm. Glass and PET are in the green area, which are suitable for displays due to their low haze and high transparency; the transparent paper developed in this work …more

"The papers are made of ribbon-like materials that can stack well without microsize cavities for high transmittance, but with nanopores for high optical haze," coauthor Liangbing Hu, Assistant Professor in the Department of Materials Science and Engineering at the University of Maryland, told Phys.org.
To test the paper for solar cell applications, the researchers coated the wood fiber paper onto the surface of a silicon slab. Experiments showed that the light-harvesting device can collect light with a 10% increase in efficiency. Due to the simplicity of this laminating process, solar cells that have already been installed and are in use could benefit similarly from the additional paper layer.

Although there are other papers made of nanofibers, this paper demonstrates a much higher optical transmittance while using much less energy and time for processing. With these advantages, the highly transparent, high-haze paper could offer an inexpensive way to enhance the efficiency of solar panels, solar roofs, and solar windows.

"We would like to work with solar cell and display companies to evaluate the applications," Hu said. "We are also interested in the manufacturing of such paper."

Explore further: Small-molecule solar cells get 50% increase in efficiency with optical spacer

More information: Zhiqiang Fang, et al. "Novel Nanostructured Paper with Ultrahigh Transparency and Ultrahigh Haze for Solar Cells." Nano Letters. DOI: 10.1021/nl404101p

Read more at: http://phys.org/news/2014-01-future-solar-cells-wood.html#jCp

 Read more at: http://phys.org/news/2014-01-future-solar-cells-wood.html#jCp

 Read more at: http://phys.org/news/2014-01-future-solar-cells-wood.html#jCp

Read more at: http://phys.org/news/2014-01-future-solar-cells-wood.html#jCp

Origins of Massive Star Explosions May Be Found

by Miriam Kramer, SPACE.com Staff Writer   |   March 07, 2013 02:01pm ET
http://www.space.com/20110-supernova-star-explosions-origins.html?cmpid=514639_20140125_17554014

              






















The key to a supernova's future is in its past, scientists say.

A new study, unveiled today (March 7), may help astronomers turn back the clock on supernovas to understand how some of these massive cosmic explosions, which signal the death of stars, can occur.
By reviewing observations of 188 supernova remnants, study leader Xiaofeng Wang, an astronomer at Tsinghua University in Beijing, and his team discovered a seemingly simple way to understand what the "progenitor" star of a stellar explosion may have looked like before the white dwarf went supernova.
 

 

Wang and his team focused specifically on a kind of star explosion known as a Type 1a supernova, which astronomers use as cosmic mile-markers to measure vast distances across galaxies. Astronomers know that Type 1a supernovas can form in one of two different scenarios, both of which include a small, dying star known as a white dwarf that is about the size of Earth, but as massive as the sun.

The team analyzed the general galactic locations of the supernovas in their survey in order to understand what the area could have looked like at the time of the actual explosion. They found the stars that went supernova in more metal-rich, and possibly younger, star systems exploded more violently than supernovas born in less metal-rich areas of a galaxy.

"The typical mass of a white dwarf is not large enough to trigger an explosion; it is suggested that either merging of two white dwarfs in a binary system or continuous accretion of mass from a companion by a white dwarf is required to reach that limit," Wang said. "But the evidence from observations are not strong enough to support one scenario and refute another one." [Amazing Photos of Supernova Explosions]

These results are one more step toward solving a mystery that has beleaguered scientists researching supernovas since the 1960s.It is likely that the more explosive supernovas are caused by a white dwarf extracting mass from a companion star like the sun or a red giant, but not another white dwarf, Wang said. The less violent supernovas are probably caused by the merging of two white dwarfs.
"The basic idea is that we use these supernovae to measure distances," Ryan Foley, an astronomer at Harvard who was not involved with the study, said. "It's how we know the universe is expanding. That's great, that we measure distances with them, but it's embarrassing that we don't yet know what stellar systems produce them."

While Wang's work is consistent with other findings, by using a broad overview of survey data, the results are not as detailed as some supernova research published in recent years, added Foley.

An earlier study led by Foley used a comprehensive examination of a group of Type 1a supernovas to see that the violently exploding stars were found in gassy environments within their area of the galaxy.

"The previous way that we've found the differences is telescope time-intensive; this new way has the potential to use very little telescope time," Foley said of Wang's work. "Overall, it's a nice result, but it's one of these things that the interpretation of the results is going to take a little time to flush out."
The research was detailed online March 7 in the journal Science.

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