(This is the topic of my dissertation, and I have also published a few articles related to it. I thought I'd try to explain it without using too much jargon for friends and family who may wonder what I've been doing with my life. :) Feedback is always appreciated!)
Stable isotopes of different elements have many interesting applications in areas such as geophysics and archaeology. While the identity of a given element is determined by the number of protons in the nucleus, the nucleus also contains a certain number of neutrons that help keep the nucleus stable. (When a nucleus has too many or too few neutrons, it will become radioactive.) These neutrons usually do not affect most of the chemistry of an element with notable exceptions. Variations in the number of neutrons do lead to different isotopes of each element with different masses, such as carbon-12 (12C), carbon-13 (13C), and carbon-14 (14C). The number next to the element is the total number of protons and neutrons, which is the atomic mass of that atom. The amount of each stable isotope on Earth stays relatively constant. For example, 13C makes up about 1.1% of all carbon on Earth. However, the differences in masses can cause small changes in the amount of each isotope in a chemical through different reactions or physical processes such as evaporation. Usually the differences between isotopes are related to their mass differences through atomic or molecular speeds in a gas or the spring-like vibrations of chemical bonds. These small changes in the amount of an isotope allow researchers to learn new information about the physical, chemical, or biological processes that affected an object.
While in almost all cases stable isotopes move and react in ways that depend on their mass, the three stable isotopes of oxygen (16O, 17O, 18O) in ozone formed in the laboratory or the atmosphere like to break the rules. Scientists expected that 16O would form ozone the fastest, 18O would form ozone the slowest, and 17O would form ozone at a speed about halfway in between. Instead, not only does 16O form ozone the slowest, but 17O and 18O form ozone at the same faster speed! To understand just how strange this is, imagine that you have three blocks of the same material and shape, one light, one heavy, and one in between. If you tried lifting each of them, the heaviest block would be the hardest to lift, the lightest block would be easiest, with the ball in between of moderate difficulty, right? What if the lightest block was hardest to lift, and then the two heavier blocks were equally easy to lift? That's a lot like what happens in ozone formation.
Scientists call this phenomenon "mass-independent", but it probably should be called "mass-bizarre". It's not necessarily unique to ozone, either. Scientists have discovered this strange isotope behavior in oxygen isotopes in some meteorites and in sulfur and mercury isotopes as well. More than a mere curiosity, the signal in the isotopes from these processes is unique and so could potentially be useful as a tool for understanding many different geophysical processes. This "mass-independent" signal finds its way into all sorts of other chemicals in the atmosphere, such as CO2. Despite its potential use as a tool to trace different processes in the atmosphere, the chemistry and physics of this weird effect remains poorly understood. Improving our understanding of what leads to these strange effects is key to using them to understand more about the Earth's atmosphere.
Friday, September 13, 2013
Friday, January 13, 2012
Buying Time on Climate Change
While much of the discussion of climate change revolves around carbon dioxide because of its primary role in increasing average global temperatures, many other chemicals other than CO2 can have an effect on the climate. Two such important contributors to global climate are the greenhouse gas methane (i.e. the primary component of natural gas) and black carbon (soot from incomplete burning). Methane is emitted by a variety of sources both natural and human such as wetlands and rice paddies, as I had discussed in a previous article about the methane cycle. Black Carbon is nothing more than the smoke common in wood fires or any kind of incomplete burning from diesel or coal burning. It also can absorb heat in the atmosphere and cause warming, and when deposited on snow or ice, can decrease its cooling ability by reducing its albedo or how much light it reflects. Both methane and soot have much shorter lifetimes than carbon dioxide in the atmosphere, at 11 years and weeks to months respectively compared to 170 years for carbon dioxide, making them attractive targets for short to medium term reductions in emissions related to climate change.
In addition to their effects on climate, methane and black carbon are also problematic emissions because they both act as precursors to photochemical smog and because black carbon is a big component of particulate emissions that are really bad for your lungs. Because reducing both these emissions would have a public health benefit beyond any changes to the climate, emission reductions of methane and black carbon could potentially be an important first stem to slowing climate change. In a recent Science article (gated), Drew Shindell, a NASA scientist, and a team of scientists and economists from around the world identified various technologies available now and possible regulations that could reduce methane and black carbon emissions immediately. They then calculating the costs of of implementing these new technologies and compared them to the potential benefits on public health, crop yields, and climate. The benefits of reducing both far outweighed the costs, in reduced impacts from changes in climate from differences in precipitation patterns, crop yields, and premature deaths. In particular, the reductions in black carbon resulted in an enormous benefit in terms of reduced premature deaths since particulate emissions such as black carbon are pretty bad for human health. Most of the benefits were realized in India and China (where black carbon emissions are much, much worse than in the United Stats or Europe) in the form of avoided changes in the precipitation patterns crucial for agriculture. However, the United States also benefited from potential increases in crop yields due to less photochemical smog from methane emissions. The ozone formed in photochemical smog, in addition to being a lung irritant, also reduces crop yields. Plants reduce atmospheric uptake in high concentrations of ozone because of its highly reactive nature, which can damage the inside of the plant as easily as it can damage your lung tissue.
For climate change, the full implementation of their recommended technologies and regulations would actually in the short to medium term help slow the pace of climate change relative to a "business as usual" scenario. This interactive graphic from NASA that accompanied this publication shows how under different "climate sensitivity" (how much the temperature changes in response to increased CO2) scenarios the implementation of CH4 (methane) and BC (black carbon) measures can reduce the expected warming. Depending on how sensitive the climate is to changes in CO2 these measures delay the time it takes to reach 2oC degree warming threshold that many scientists consider to be a dangerous threshold for the climate. This gives all of us some "breathing room" (so to speak) to develop alternatives to fossil fuel burning as a source of energy because even with these measures CO2 is still the primary mover of climate change. Many times it's extremely under-appreciated just how challenging it is to develop alternatives to fossil fuels as it may be decades before a true alternative can be developed. This study gives us hope that we can eventually tackle climate change without dramatic changes to living standards or a halt to the increasing prosperity that free trade and liberalizing reforms are bringing to the developing world.
Related Links:
An interview with Drew Shindell, the primary author of this study
In addition to their effects on climate, methane and black carbon are also problematic emissions because they both act as precursors to photochemical smog and because black carbon is a big component of particulate emissions that are really bad for your lungs. Because reducing both these emissions would have a public health benefit beyond any changes to the climate, emission reductions of methane and black carbon could potentially be an important first stem to slowing climate change. In a recent Science article (gated), Drew Shindell, a NASA scientist, and a team of scientists and economists from around the world identified various technologies available now and possible regulations that could reduce methane and black carbon emissions immediately. They then calculating the costs of of implementing these new technologies and compared them to the potential benefits on public health, crop yields, and climate. The benefits of reducing both far outweighed the costs, in reduced impacts from changes in climate from differences in precipitation patterns, crop yields, and premature deaths. In particular, the reductions in black carbon resulted in an enormous benefit in terms of reduced premature deaths since particulate emissions such as black carbon are pretty bad for human health. Most of the benefits were realized in India and China (where black carbon emissions are much, much worse than in the United Stats or Europe) in the form of avoided changes in the precipitation patterns crucial for agriculture. However, the United States also benefited from potential increases in crop yields due to less photochemical smog from methane emissions. The ozone formed in photochemical smog, in addition to being a lung irritant, also reduces crop yields. Plants reduce atmospheric uptake in high concentrations of ozone because of its highly reactive nature, which can damage the inside of the plant as easily as it can damage your lung tissue.
For climate change, the full implementation of their recommended technologies and regulations would actually in the short to medium term help slow the pace of climate change relative to a "business as usual" scenario. This interactive graphic from NASA that accompanied this publication shows how under different "climate sensitivity" (how much the temperature changes in response to increased CO2) scenarios the implementation of CH4 (methane) and BC (black carbon) measures can reduce the expected warming. Depending on how sensitive the climate is to changes in CO2 these measures delay the time it takes to reach 2oC degree warming threshold that many scientists consider to be a dangerous threshold for the climate. This gives all of us some "breathing room" (so to speak) to develop alternatives to fossil fuel burning as a source of energy because even with these measures CO2 is still the primary mover of climate change. Many times it's extremely under-appreciated just how challenging it is to develop alternatives to fossil fuels as it may be decades before a true alternative can be developed. This study gives us hope that we can eventually tackle climate change without dramatic changes to living standards or a halt to the increasing prosperity that free trade and liberalizing reforms are bringing to the developing world.
Related Links:
An interview with Drew Shindell, the primary author of this study
Friday, January 6, 2012
Nuclear Bomb Testing and Boreal Forest Fires
One important piece of evidence that shows that climate change has been caused by humans is the decrease in the amount of radiocarbon (carbon-14) in CO2. You may be familiar with carbon-14 because of its use in radiocarbon dating in archaeology for objects up to 60,000 years old. For those unfamiliar, though, carbon-14 is produced in the upper atmosphere by reaction of neutrons from cosmic rays with nitrogen. The carbon-14 produced is then eventually transported to the lower atmosphere, where plants uptake the 14CO2 via photosynthesis. Once a plant dies, it stops absorbing carbon dioxide, which then causes any of the carbon-14 in the leftover plant material to radioactively decay. As such, fossil fuels, having been in the ground for millions of years, contain almost no carbon-14, so that when they are burned, the carbon dioxide produced has no carbon-14 content.
Of course, measuring carbon-14 in CO2 in the atmosphere has several complications associated with it. In an article in the Journal of Geophysical Research, a group of scientists from NASA, NOAA, and various universities around the world measured CO2 and its carbon-14 content from air samples collected on aircraft campaigns over the Arctic in Canada. As you might expect from my above explanation, CO2 from right over the Alberta tar sands has both higher concentrations and reduced carbon-14 content compared to typical levels for background CO2 from emissions from burning the oil extracted. Interestingly, some of the air samples that were far from any influence from civilization also had higher concentrations of CO2 but increased carbon-14 content. High levels of carbon monoxide in these samples along with some atmospheric modeling (and a little knowledge of local conditions) led the scientists to conclude that these measurements were sampling air from boreal forest fires in the Arctic. Why would this lead to higher carbon-14, though?
The above plot with the amount of carbon-14 in the atmosphere over the last few decades helps show what likely caused this increase in the carbon-14 content. During the 1950's and into the 1960's, the world's governments conducted many nuclear bomb tests in the atmosphere, which released a lot of neutrons into the atmosphere. Since neutrons cause the formation of carbon-14 from nitrogen as explained above, this nuclear testing caused a so-called "bomb spike" in carbon-14 until atmospheric nuclear testing was banned internationally in the 60's from health concerns about the release of other much more radioactive isotopes of elements such as strontium-90 into the atmosphere. Because plants continuously absorb CO2 throughout their lifetimes, decades-old trees in boreal forests in the Arctic could retain high levels of carbon-14 until burned by a sudden forest fire, releasing highly enriched carbon-14 back into the atmosphere.
The results in this paper highlight some of the challenges involved in the use of carbon-14 as a tracer of fossil fuel burning. However, it also shows the incredible utility of trace isotope studies in providing information about the chemical processes in the atmosphere. Using isotopes, much more information can be gained about a chemical than from simply looking at the amount present alone.
Of course, measuring carbon-14 in CO2 in the atmosphere has several complications associated with it. In an article in the Journal of Geophysical Research, a group of scientists from NASA, NOAA, and various universities around the world measured CO2 and its carbon-14 content from air samples collected on aircraft campaigns over the Arctic in Canada. As you might expect from my above explanation, CO2 from right over the Alberta tar sands has both higher concentrations and reduced carbon-14 content compared to typical levels for background CO2 from emissions from burning the oil extracted. Interestingly, some of the air samples that were far from any influence from civilization also had higher concentrations of CO2 but increased carbon-14 content. High levels of carbon monoxide in these samples along with some atmospheric modeling (and a little knowledge of local conditions) led the scientists to conclude that these measurements were sampling air from boreal forest fires in the Arctic. Why would this lead to higher carbon-14, though?
The above plot with the amount of carbon-14 in the atmosphere over the last few decades helps show what likely caused this increase in the carbon-14 content. During the 1950's and into the 1960's, the world's governments conducted many nuclear bomb tests in the atmosphere, which released a lot of neutrons into the atmosphere. Since neutrons cause the formation of carbon-14 from nitrogen as explained above, this nuclear testing caused a so-called "bomb spike" in carbon-14 until atmospheric nuclear testing was banned internationally in the 60's from health concerns about the release of other much more radioactive isotopes of elements such as strontium-90 into the atmosphere. Because plants continuously absorb CO2 throughout their lifetimes, decades-old trees in boreal forests in the Arctic could retain high levels of carbon-14 until burned by a sudden forest fire, releasing highly enriched carbon-14 back into the atmosphere.
The results in this paper highlight some of the challenges involved in the use of carbon-14 as a tracer of fossil fuel burning. However, it also shows the incredible utility of trace isotope studies in providing information about the chemical processes in the atmosphere. Using isotopes, much more information can be gained about a chemical than from simply looking at the amount present alone.
Wednesday, October 19, 2011
Climate Change, Photosynthesis, and El Niño
The way carbon is moved between the atmosphere, the biosphere, oceans, and other parts of the Earth system plays an important role in the current scientific consensus on climate change. While the various processes involved are known well enough to predict that the planet will continue warming if CO2 concentrations keep increasing from fossil fuel emissions, better understanding of any part of the so-called carbon cycle can improve predictions of how exactly how much warming will occur. The image below shows a model of the carbon cycle.
In particular, the approximation of the conversion of CO2 to sugars by plants during photosynthesis (called primary production) could have its range of possible quantities narrowed. In a recent study in the journal Nature, the authors use measurements the rare, stable oxygen isotope, oxygen-18, in CO2 to estimate the value of primary production. Since CO2 can exchange oxygen atoms with water in leaves without undergoing photosynthesis, the ratio of oxygen-18 to oxygen-16 in CO2 is related to how much CO2 is converted to sugars in plants. Using these measurements, they actually found that primary production might be greater than previously thought! Their estimate has the advantage of not relying on assumptions about biology and provides further constraints on primary production. This increase in the estimate of primary production certainly may turn out to be good news because it could mean that CO2 concentrations will rise (slightly) more slowly. However, especially because primary production does not count how much of the sugars produced are consumed by the plant itself (and thus changed back into CO2), it does unfortunately not mean that the biosphere can completely offset all changes in CO2 from fossil fuel emissions.
By observing the oxygen-18 to oxygen-16 ratio over 30 years at various locations around the world, the scientists found occasional small increases in the ratio from year to year. Oddly enough, these increases occurred at the same time as El Niño! They explained this increase in the oxygen-18 to oxygen-16 ratio by decreases in rainfall over rain forests (where lots of photosynthesis occurs) in Southeast Asia and northern South America during El Niño. Because the water with oxygen-18 is "heavier" than water with oxygen-16, the water in clouds tends to have more oxygen-16 since "lighter" oxygen-16 containing water evaporates first. During periods with less rainfall, the water still evaporates over rainforests, reducing the amount of oxygen-16 in water in the soil. Without enough rainfall to return oxygen-16 back to the ground, the relative amount of oxygen-18 increases, thus the water in plant leaves also has more oxygen-18. Although this effect is very small (a 0.05% change), it can be measured in CO2. As the southern ocean returns to a La Niña pattern and rainfall in these regions increases, the oxygen-18 to oxygen-16 ratio in CO2 eventually returns to its "normal" level. The scientists used the rate of change in oxygen-18 to calculate an estimate of primary productivity. Additional measurements of oxygen-17 to oxygen-16 ratios may provide additional constraints to help improve this estimate further. (For a more detailed explanation of isotopes in geology and chemistry, see this previous post)
(h/t Jeremiah J.)
In particular, the approximation of the conversion of CO2 to sugars by plants during photosynthesis (called primary production) could have its range of possible quantities narrowed. In a recent study in the journal Nature, the authors use measurements the rare, stable oxygen isotope, oxygen-18, in CO2 to estimate the value of primary production. Since CO2 can exchange oxygen atoms with water in leaves without undergoing photosynthesis, the ratio of oxygen-18 to oxygen-16 in CO2 is related to how much CO2 is converted to sugars in plants. Using these measurements, they actually found that primary production might be greater than previously thought! Their estimate has the advantage of not relying on assumptions about biology and provides further constraints on primary production. This increase in the estimate of primary production certainly may turn out to be good news because it could mean that CO2 concentrations will rise (slightly) more slowly. However, especially because primary production does not count how much of the sugars produced are consumed by the plant itself (and thus changed back into CO2), it does unfortunately not mean that the biosphere can completely offset all changes in CO2 from fossil fuel emissions.
By observing the oxygen-18 to oxygen-16 ratio over 30 years at various locations around the world, the scientists found occasional small increases in the ratio from year to year. Oddly enough, these increases occurred at the same time as El Niño! They explained this increase in the oxygen-18 to oxygen-16 ratio by decreases in rainfall over rain forests (where lots of photosynthesis occurs) in Southeast Asia and northern South America during El Niño. Because the water with oxygen-18 is "heavier" than water with oxygen-16, the water in clouds tends to have more oxygen-16 since "lighter" oxygen-16 containing water evaporates first. During periods with less rainfall, the water still evaporates over rainforests, reducing the amount of oxygen-16 in water in the soil. Without enough rainfall to return oxygen-16 back to the ground, the relative amount of oxygen-18 increases, thus the water in plant leaves also has more oxygen-18. Although this effect is very small (a 0.05% change), it can be measured in CO2. As the southern ocean returns to a La Niña pattern and rainfall in these regions increases, the oxygen-18 to oxygen-16 ratio in CO2 eventually returns to its "normal" level. The scientists used the rate of change in oxygen-18 to calculate an estimate of primary productivity. Additional measurements of oxygen-17 to oxygen-16 ratios may provide additional constraints to help improve this estimate further. (For a more detailed explanation of isotopes in geology and chemistry, see this previous post)
(h/t Jeremiah J.)
Thursday, October 6, 2011
Super soggy air on Mars
Using observations from the SPICAM instrument on the European Space Agency's Mars probe Mars Express, French scientists discovered that the amount of water vapor in the upper Martian atmosphere sometimes far exceeds expectations. While some water vapor is formed from sublimation (evaporation) off ice on the Marian surface, the amount found in the upper atmosphere is greater than the temperature would predict. In terms of relative humidity, the humidity of the air was observed to approach almost as much as 1000%! Scientists call such air "supersaturated" in water, since the air is holding far more water than it would otherwise.
How could so much extra water end up in the atmosphere of Mars? The authors suggest that the low pressure and lack of dust particles in the upper atmosphere make condensation into ice very difficult, so that the water simply stays in vapor form. Simultaneous measurements of the amount of dust show that this could indeed be the case. These results fundamentally change scientists understanding of the water cycle on Mars as water vapor exists in much higher concentrations at higher altitudes than previous thought. Greater amounts of water vapor in the upper Martian atmosphere imply that a larger amount of water is able to escape Mars's gravity than previously thought. Models of the chemistry of the Martian atmosphere are also affected by water - despite its relatively low amounts (even with this result) water acts as a catalyst in many chemical cycles in the Martian atmosphere.
How could so much extra water end up in the atmosphere of Mars? The authors suggest that the low pressure and lack of dust particles in the upper atmosphere make condensation into ice very difficult, so that the water simply stays in vapor form. Simultaneous measurements of the amount of dust show that this could indeed be the case. These results fundamentally change scientists understanding of the water cycle on Mars as water vapor exists in much higher concentrations at higher altitudes than previous thought. Greater amounts of water vapor in the upper Martian atmosphere imply that a larger amount of water is able to escape Mars's gravity than previously thought. Models of the chemistry of the Martian atmosphere are also affected by water - despite its relatively low amounts (even with this result) water acts as a catalyst in many chemical cycles in the Martian atmosphere.
Thursday, September 22, 2011
The Scientific Process and Ship Wakes
This article from the open-access journal Atmospheric Chemistry and Physics was actually rejected to be published by the journal in 2010. Because of the open-access model of the journal, the originally submitted article along with reviewer comments can be viewed despite the article's rejection. In the article, the authors measured the amount of light reflected by the wakes from shipping barges in the northern Pacific Ocean from airplanes. They then used their results to estimate the increase in reflected sunlight from increases in shipping across the Pacific, since this would have a (very) small cooling effect on the climate. Unfortunately, while this was a somewhat clever idea, the reviewers thought that there were far too many uncertainties in both their measurements and calculations so that the reported number was an overestimate of an already small number.
While this article was rejected, because of the open-access nature of the journal, it shows how the scientific process of peer review works. Typically, when science and the scientific method is taught in schools, the curriculum focuses on the experimental process of science. While certainly this is very important, science also has important social ways of processing new information. If a group of scientists do a series of experiments that reach new and interesting conclusions, they will try to get their results published to a scientific journal. (And present this information at conferences, universities, research centers, etc.) Upon submission to a journal, two (or more) other scientists from the same research field will read the initial paper, either recommending that the results be published along with potential changes or that the paper be rejected outright. If the paper is rejected, the authors can appeal to have it accepted, but this is not usually granted. The authors then edit the paper based on the suggestions of the reviewers, and it is resubmitted and published in the next issue of the journal. Usually a reader only sees the final product of this process in a scientific journal, but in the case of an open-access journal such as Atmospheric Chemistry and Physics the entire process is visible to the reader (and the journal is free online). Even articles that eventually are rejected such as this one are immediately put on the journal's website after a quick review process to ensure the article is relevant.
Peer review is an important process to ensure quality as scientists being human after all are prone to misjudgment, bias, or error. While science is constantly changing over time as new ideas or methods are realized, it's important to make sure these ideas are plausible or methods actually work! While there are many cases of new ideas overturning the scientific consensus (I'm looking at you, quantum mechanics) it's often after these new ideas have been thoroughly scrutinized and verified through the process of peer review, discussions at scientific conferences, and independent testing of observations or experiments. The process is not without its faults, of course! Occasionally a scientist will unethically use peer review to block the publication of results that contradict their own. (Yes, it's kind of silly. There is the joke: "The debates in science are so fierce because the stakes are so low." I've seen people spend 15 minutes at a conference arguing about what the proper term for something is.) In those cases, an open access journal such as Atmospheric Chemistry and Physics provides the kind of transparency that makes such cases apparent to improve the scientific process. Hopefully with the growing use of information technology (I know I rarely ever read the actual printed journal) more publishers decide to switch to an open-access model not only for transparency but to improve access to scientific journals to the general public.
While this article was rejected, because of the open-access nature of the journal, it shows how the scientific process of peer review works. Typically, when science and the scientific method is taught in schools, the curriculum focuses on the experimental process of science. While certainly this is very important, science also has important social ways of processing new information. If a group of scientists do a series of experiments that reach new and interesting conclusions, they will try to get their results published to a scientific journal. (And present this information at conferences, universities, research centers, etc.) Upon submission to a journal, two (or more) other scientists from the same research field will read the initial paper, either recommending that the results be published along with potential changes or that the paper be rejected outright. If the paper is rejected, the authors can appeal to have it accepted, but this is not usually granted. The authors then edit the paper based on the suggestions of the reviewers, and it is resubmitted and published in the next issue of the journal. Usually a reader only sees the final product of this process in a scientific journal, but in the case of an open-access journal such as Atmospheric Chemistry and Physics the entire process is visible to the reader (and the journal is free online). Even articles that eventually are rejected such as this one are immediately put on the journal's website after a quick review process to ensure the article is relevant.
Peer review is an important process to ensure quality as scientists being human after all are prone to misjudgment, bias, or error. While science is constantly changing over time as new ideas or methods are realized, it's important to make sure these ideas are plausible or methods actually work! While there are many cases of new ideas overturning the scientific consensus (I'm looking at you, quantum mechanics) it's often after these new ideas have been thoroughly scrutinized and verified through the process of peer review, discussions at scientific conferences, and independent testing of observations or experiments. The process is not without its faults, of course! Occasionally a scientist will unethically use peer review to block the publication of results that contradict their own. (Yes, it's kind of silly. There is the joke: "The debates in science are so fierce because the stakes are so low." I've seen people spend 15 minutes at a conference arguing about what the proper term for something is.) In those cases, an open access journal such as Atmospheric Chemistry and Physics provides the kind of transparency that makes such cases apparent to improve the scientific process. Hopefully with the growing use of information technology (I know I rarely ever read the actual printed journal) more publishers decide to switch to an open-access model not only for transparency but to improve access to scientific journals to the general public.
Wednesday, September 14, 2011
Variations in Volcanic Dust High Up
Last month, in Science magazine, Susan Solomon,* an atmospheric chemist at the National Oceanic and Atmospheric Administration (NOAA) and her colleagues presented satellite measurements of sulfate aerosols in volcanic dust in the stratosphere, the upper region of the atmosphere that contains the ozone layer. These measurements showed that the levels of volcanic dust in the stratosphere actually vary significantly even in the absence of major volcanic eruptions such as the Mount Pinatubo eruption in 1991.
Aerosols such as this volcanic dust scatter and reflect light from the sun, thus causing a net cooling of the climate. The volcanic dust in the stratosphere actually increased (mostly from natural volcanic events) enough from 2000 to 2010 to decrease the heat trapped by the atmosphere by 0.1 W/m2. For comparison, the increase in CO2 during the same period increased the heat trapped by the atmosphere by 0.28 W/m2, thus this volcanic dust cancelled out some of the warming that would have occurred from CO2 alone. While this is certainly a good thing as it has slowed the pace of global warming, it is unclear whether this increase in volcanic dust will continue due to the unpredictable nature of volcanic activity. For example, if by 2020 volcanic dust were to return to levels seen in the 1960, any cooling effect would disappear and cause average global temperature to increase by 0.06oC in addition to any changes from increased greenhouse gases. Despite the inherit unpredictability of volcanic activity, understanding that volcanic dust does have variable effects on the climate over time can help better constrain the possible range of any future changes in the climate.
Implications
In a broader sense, aerosols (i.e. dust and liquid droplets floating in air) are an important part of the climate change picture that are often under-discussed compared to poor, infamous CO2. Changes in aerosols caused by humans from land use, transportation (autos, trains, etc.), and industry (smoke stacks) since the industrial revolution have increased the light reflected by the Earth. Much like the volcanic dust in the stratosphere, this has reduced the heat trapped by the atmosphere, partially offsetting the increased heat trapped by greenhouse gases. In the period from 1940 to 1980, the combined effect of these two might have canceled each other out for a time, leading some to speculate about the possibility of global cooling in the 1970's. Of course, this hypothesis has not been borne out by the data since then. Aerosols have negative effects on humans directly through inhalation or indirectly through smog and acid rain, so government regulation of these pollutants has reduced their concentration in the atmosphere. While this is an obviously good thing for human society, it had the unfortunate effect of reducing their cooling effect on the atmosphere!
Studies like this one are especially important for improving climate predictions, as aerosols are the least well-understood part of climate change, especially because of their indirect effects on cloud formation. (See this chart from the IPCC and notice the very large black bars on aerosols compared to other factors.) They're certainly understood enough to predict that the Earth is warming and will continue to warm without any changes in human activity, but predicting how much the climate might change in the future is constrained largely by the uncertainty in the effects of aerosols. Better understanding the impact of aerosols, both human-made and natural, can improve the uncertainty in future predictions of climate. This, in turn, can provide better estimates of the costs and benefits of any potential emissions reductions or even geoengineering.
*Susan Solomon has won the US National Medal of Science for her work on understanding the cause of ozone depletion, and was one of the co-chairs of the physical science report for the International Panel on Climate Change.
Aerosols such as this volcanic dust scatter and reflect light from the sun, thus causing a net cooling of the climate. The volcanic dust in the stratosphere actually increased (mostly from natural volcanic events) enough from 2000 to 2010 to decrease the heat trapped by the atmosphere by 0.1 W/m2. For comparison, the increase in CO2 during the same period increased the heat trapped by the atmosphere by 0.28 W/m2, thus this volcanic dust cancelled out some of the warming that would have occurred from CO2 alone. While this is certainly a good thing as it has slowed the pace of global warming, it is unclear whether this increase in volcanic dust will continue due to the unpredictable nature of volcanic activity. For example, if by 2020 volcanic dust were to return to levels seen in the 1960, any cooling effect would disappear and cause average global temperature to increase by 0.06oC in addition to any changes from increased greenhouse gases. Despite the inherit unpredictability of volcanic activity, understanding that volcanic dust does have variable effects on the climate over time can help better constrain the possible range of any future changes in the climate.
Implications
In a broader sense, aerosols (i.e. dust and liquid droplets floating in air) are an important part of the climate change picture that are often under-discussed compared to poor, infamous CO2. Changes in aerosols caused by humans from land use, transportation (autos, trains, etc.), and industry (smoke stacks) since the industrial revolution have increased the light reflected by the Earth. Much like the volcanic dust in the stratosphere, this has reduced the heat trapped by the atmosphere, partially offsetting the increased heat trapped by greenhouse gases. In the period from 1940 to 1980, the combined effect of these two might have canceled each other out for a time, leading some to speculate about the possibility of global cooling in the 1970's. Of course, this hypothesis has not been borne out by the data since then. Aerosols have negative effects on humans directly through inhalation or indirectly through smog and acid rain, so government regulation of these pollutants has reduced their concentration in the atmosphere. While this is an obviously good thing for human society, it had the unfortunate effect of reducing their cooling effect on the atmosphere!
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Studies like this one are especially important for improving climate predictions, as aerosols are the least well-understood part of climate change, especially because of their indirect effects on cloud formation. (See this chart from the IPCC and notice the very large black bars on aerosols compared to other factors.) They're certainly understood enough to predict that the Earth is warming and will continue to warm without any changes in human activity, but predicting how much the climate might change in the future is constrained largely by the uncertainty in the effects of aerosols. Better understanding the impact of aerosols, both human-made and natural, can improve the uncertainty in future predictions of climate. This, in turn, can provide better estimates of the costs and benefits of any potential emissions reductions or even geoengineering.
*Susan Solomon has won the US National Medal of Science for her work on understanding the cause of ozone depletion, and was one of the co-chairs of the physical science report for the International Panel on Climate Change.
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