Adjusting Earth’s thermostat, with caution

David Keith, Gordon McKay Professor of Applied Physics at Harvard SEAS and professor of public policy at Harvard Kennedy School, coauthored several papers on climate engineering with colleagues at Harvard and beyond. -  Eliza Grinnell, SEAS Communications.
David Keith, Gordon McKay Professor of Applied Physics at Harvard SEAS and professor of public policy at Harvard Kennedy School, coauthored several papers on climate engineering with colleagues at Harvard and beyond. – Eliza Grinnell, SEAS Communications.

A vast majority of scientists believe that the Earth is warming at an unprecedented rate and that human activity is almost certainly the dominant cause. But on the topics of response and mitigation, there is far less consensus.

One of the most controversial propositions for slowing the increase in temperatures here on Earth is to manipulate the atmosphere above. Specifically, some scientists believe it should be possible to offset the warming effect of greenhouses gases by reflecting more of the sun’s energy back into space.

The potential risks–and benefits–of solar radiation management (SRM) are substantial. So far, however, all of the serious testing has been confined to laboratory chambers and theoretical models. While those approaches are valuable, they do not capture the full range of interactions among chemicals, the impact of sunlight on these reactions, or multiscale variations in the atmosphere.

Now, a team of researchers from the Harvard School of Engineering and Applied Sciences (SEAS) has outlined how a small-scale “stratospheric perturbation experiment” could work. By proposing, in detail, a way to take the science of geoengineering to the skies, they hope to stimulate serious discussion of the practice by policymakers and scientists.

Ultimately, they say, informed decisions on climate policy will need to rely on the best information available from controlled and cautious field experiments.

The paper is among several published today in a special issue of the Philosophical Transactions of the Royal Society A that examine the nuances, the possible consequences, and the current state of scientific understanding of climate engineering. David Keith, whose work features prominently in the issue, is Gordon McKay Professor of Applied Physics at Harvard SEAS and a professor of public policy at Harvard Kennedy School. His coauthors on the topic of field experiments include James Anderson, Philip S. Weld Professor of Applied Chemistry at Harvard SEAS and in Harvard’s Department of Chemistry and Chemical Biology; and other colleagues at Harvard SEAS.

“The idea of conducting experiments to alter atmospheric processes is justifiably controversial, and our experiment, SCoPEx, is just a proposal,” Keith emphasizes. “It will continue to evolve until it is funded, and we will only move ahead if the funding is substantially public, with a formal approval process and independent risk assessment.”

With so much at stake, Keith believes transparency is essential. But the science of climate engineering is also widely misunderstood.

“People often claim that you cannot test geoengineering except by doing it at full scale,” says Keith. “This is nonsense. It is possible to do a small-scale test, with quite low risks, that measures key aspects of the risk of geoengineering–in this case the risk of ozone loss.”

Such controlled experiments, targeting key questions in atmospheric chemistry, Keith says, would reduce the number of “unknown unknowns” and help to inform science-based policy.

The experiment Keith and Anderson’s team is proposing would involve only a tiny amount of material–a few hundred grams of sulfuric acid, an amount Keith says is roughly equivalent to what a typical commercial aircraft releases in a few minutes while flying in the stratosphere. It would provide important insight into how much SRM would reduce radiative heating, the concentration of water vapor in the stratosphere, and the processes that determine water vapor transport–which affects the concentration of ozone.

In addition to the experiment proposed in that publication, another paper coauthored by Keith and collaborators at the California Institute of Technology (CalTech) collects and reviews a number of other experimental methods, to demonstrate the diversity of possible approaches.

“There is a wide range of experiments that could be done that would significantly reduce our uncertainty about the risks and effectiveness of solar geoengineering,” Keith says. “Many could be done with very small local risks.”

A third paper explores how solar geoengineering might actually be implemented, if an international consensus were reached, and suggests that a gradual implementation that aims to limit the rate of climate change would be a plausible strategy.

“Many people assume that solar geoengineering would be used to suddenly restore the Earth’s climate to preindustrial temperatures,” says Keith, “but it’s very unlikely that it would make any policy sense to try to do so.”

Keith also points to another paper in the Royal Society’s special issue–one by Andy Parker at the Belfer Center for Science and International Affairs at Harvard Kennedy School. Parker’s paper furthers the discussion of governance and good practices in geoengineering research in the absence of both national legislation and international agreement, a topic raised last year in Science by Keith and Edward Parson of UCLA.

“The scientific aspects of geoengineering research must, by necessity, advance in tandem with a thorough discussion of the social science and policy,” Keith warns. “Of course, these risks must also be weighed against the risk of doing nothing.”

For further information, see: “Stratospheric controlled perturbation experiment (SCoPEx): A small-scale experiment to improve understanding of the risks of solar geoengineering” doi: 10.1098/rsta.2014.0059

By John Dykema, project scientist at Harvard SEAS; David Keith, Gordon McKay Professor of Applied Physics at Harvard SEAS and professor of public policy at Harvard Kennedy School; James Anderson, Philip S. Weld Professor of Applied Chemistry at Harvard SEAS and in Harvard’s Department of Chemistry and Chemical Biology; and Debra Weisenstein, research management specialist at Harvard SEAS.

“Field experiments on solar geoengineering: Report of a workshop exploring a representative research portfolio”
doi: 10.1098/rsta.2014.0175

By David Keith; Riley Duren, chief systems engineer at the NASA Jet Propulsion Laboratory at CalTech; and Douglas MacMartin, senior research associate and lecturer at CalTech.

“Solar geoengineering to limit the rate of temperature change”
doi: 10.1098/rsta.2014.0134

By Douglas MacMartin; Ken Caldeira, senior scientist at the Carnegie Institute for Science and professor of environmental Earth system sciences at Stanford University; and David Keith.

“Governing solar geoengineering research as it leaves the laboratory”
doi: 10.1098/rsta.2014.0173

By Andy Parker, associate of the Belfer Center at Harvard Kennedy School.

Sea-level spikes, volcanic risk, volcanos cause drought

Unforeseen, short-term increases in sea level caused by strong winds, pressure changes and fluctuating ocean currents can cause more damage to beaches on the East Coast over the course of a year than a powerful hurricane making landfall, according to a new study. The new research suggests that these sea-level anomalies could be more of a threat to coastal homes and businesses than previously thought, and could become higher and more frequent as a result of climate change, according to a new study accepted for publication in Geophysical Research Letters, a journal of the American Geophysical Union.

From this week’s Eos: Assessing Volcanic Risk in Saudi Arabia: An Integrated Approach

The Kingdom of Saudi Arabia has numerous large volcanic fields, known locally as “harrats.” The largest of these, Harrat Rahat, produced a basaltic fissure eruption in 1256 A.D. with lava flows traveling within 20 kilometers of the city Al-Madinah, which has a current population of 1.5 million plus an additional 3 million pilgrims annually. With more than 950 visible vents and periodic seismic swarms, an understanding of the risk of future eruptions in this volcanic field is vital. The Volcanic Risk in Saudi Arabia (VORISA) project was developed as a multidisciplinary international research collaboration that integrates geological, geophysical, hazard, and risk studies in this important area.

From AGU’s journals: Large volcanic eruptions cause drought in eastern China

In most cases, the annual East Asian Monsoon brings heavy rains and widespread flooding to southeast China and drought conditions to the northeast. At various points throughout history, however, large volcanic eruptions have upset the regular behavior of the monsoon.

Sulfate aerosols injected high into the atmosphere by powerful eruptions can lower the land-sea temperature contrast that powers the monsoon circulation. How this altered aerosol forcing affects precipitation is not entirely clear, however, as climate models do not always agree with observations of the nature and scale of the effect.

Using two independent records of historical volcanic activity along with two different measures of rainfall, including one 3,000-year long record derived from local flood and drought observations, Zhuo et al. analyzes how large volcanic eruptions changed the conditions on the ground for the period 1368 to 1911. Understanding the effect of sulfate aerosols on monsoon behavior is particularly important now, as researchers explore aerosol seeding as a means of climate engineering.

The authors find that large Northern Hemispheric volcanic eruptions cause strong droughts in much of eastern China. The drought begins in the north in the second or third summer following an eruption and slowly moves southward over the next 2 to 3 years. They find that the severity of the drought scales with the amount of aerosol injected into the atmosphere, and that it takes 4 to 5 years for precipitation to recover. The drying pattern agrees with observations from three large modern eruptions.

China’s northeast is the country’s major grain-producing region. The results suggest that any geoengineering schemes meant to mimic the effect of a large volcanic eruption could potentially trigger devastating consequences for China’s food supply.

Embarking on geoengineering, then stopping, would speed up global warming

Spraying reflective particles into the atmosphere to reflect sunlight and then stopping it could exacerbate the problem of climate change, according to new research by atmospheric scientists at the University of Washington.

Carrying out geoengineering for several decades and then stopping would cause warming at a rate that will greatly exceed that expected due to global warming, according to a study published Feb. 18 in Environmental Research Letters.

“The absolute temperature ends up being roughly the same as what it would have been, but the rate of change is so drastic, that ecosystems and organisms would have very little time to adapt to the changes,” said lead author Kelly McCusker, who did the work for her UW doctoral thesis.

The study looks at solar radiation management, a proposed method of geoengineering by spraying tiny sulfur-based particles into the upper atmosphere to reflect sunlight. This is similar to what happens after a major volcanic eruption, and many experts believe the technique is economically and technically feasible. But continuous implementation over years depends on technical functioning, continuous funding, bureaucratic agreement and lack of negative side effects.

The UW team used a global climate model to show that if an business-as-usual emissions pathway is followed up until 2035, allowing temperatures to rise 1°C above the 1970-1999 mean, and then geoengineering is implemented for 25 years and suddenly stopped, global temperatures could rise by 4°C in the following three decades, a rate more than double what it would have been otherwise, and one that exceeds historical temperature trends.

“The rate of standard projected global warming alone is going to be really detrimental to a lot of organisms, so if you increase that by a factor of 2 to 3, then those organisms are going to have an even harder time adapting or migrating,” said McCusker, now a postdoctoral researcher at the University of Victoria in Canada.

The results build on recent work led by British researchers pointing to the risk of implementing and then stopping geoengineering. That study compared several climate models, showing that the result is not specific to any one model. The UW researchers used a single model with a more realistic scenario, where instead of simply decreasing the strength of the sun they actually simulated sulfate particles to stabilize the temperature, allowing a more precise look at the spatial and seasonal pattern of the response.

“The changes that will be needed to adapt to a warmer climate are really profound,” said co-author David Battisti, a UW professor of atmospheric sciences. “The faster the climate changes, the less time farmers have to develop new agricultural practices, and the less time plants and animals have to move or evolve.”

The total amount of warming after stopping geoengineering would be largest in winter near the poles, but compared to typical historical rates of change they found that changes would be most extreme in the tropics in summertime, where there is usually very little temperature variation.

“According to our simulations, tropical regions like South Asia and sub-Saharan Africa will be hit particularly hard, the very same regions that are home to many of the world’s most food insecure populations,” McCusker said. “The potential temperature changes also pose a severe threat to biodiversity.”

The researchers looked at different variables and found that the rate of warming is largely determined by the length of time that geoengineering is deployed and the amount of greenhouse gases emitted during that time, rather than by how sensitive the climate is to changes in greenhouse-gas concentrations.

“If we must geoengineer, it does not give us an excuse to keep emitting greenhouse gases,” McCusker said. “On the contrary, our results demonstrate that if geoengineering is ever deployed, it’s imperative that greenhouse gases be reduced at the same time to reduce the risk of rapid warming.”

The research was funded by the Tamaki Foundation, the National Science Foundation and the James S. McDonnell Foundation. Other co-authors are Cecilia Bitz, a UW professor of atmospheric sciences, and Kyle Armour, a former UW doctoral student now at the Massachusetts Institute of Technology.

Researchers warn against abrupt stop to geoengineering method

As a range of climate change mitigation scenarios are discussed, University of Washington researchers have found that the injection of sulfate particles into the atmosphere to reflect sunlight and curb the effects of global warming could pose a severe threat if not maintained indefinitely and supported by strict reductions in greenhouse gas (GHG) emissions.

The new study, published today, 18 February, in IOP Publishing’s journal Environmental Research Letters, has highlighted the risks of large and spatially expansive temperature increases if solar radiation management (SRM) is abruptly stopped once it has been implemented.

SRM is a proposed method of geoengineering whereby tiny sulfate-based aerosols are released into the upper atmosphere to reflect sunlight and cool the planet. The technique has been shown to be economically and technically feasible; however, its efficacy depends on its continued maintenance, without interruption from technical faults, global cooperation breakdown or funding running dry.

According to the study, global temperature increases could more than double if SRM is implemented for a multi-decadal period of time and then suddenly stopped, in relation to the temperature increases expected if SRM was not implemented at all.

The researchers used a global climate model to show that if an extreme emissions pathway-RCP8.5-is followed up until 2035, allowing temperatures to rise 1°C above the 1970-1999 mean, and then SRM is implemented for 25 years and suddenly stopped, global temperatures could increase by 4°C in the following decades.

This rate of increase, caused by the build-up of background greenhouse gas emissions, would be well beyond the bounds experienced in the last century and more than double the 2°C temperature increase that would occur in the same timeframe if SRM had not been implemented.

On a regional and seasonal scale, the temperature changes would be largest in an absolute sense in winter over high latitude land, but compared to historical fluctuations, temperature changes would be largest in the tropics in summertime, where there is usually very little variation.

Lead author of the research, Kelly McCusker, from the University of Washington, said: “According to our simulations, tropical regions like South Asia and Sub-Saharan Africa are hit particularly hard, the very same regions that are home to many of the world’s most food insecure populations. The potential temperature changes also pose a severe threat to biodiversity.”

Furthermore, the researchers used a simple climate model to study a variety of plausible greenhouse gas scenarios and SRM termination years over the 21st century. They showed that climate sensitivity-a measure of how much the climate will warm in response to the greenhouse effect-had a lesser impact on the rate of temperature changes.

Instead, they found that the rates of temperature change were determined by the amount of GHG emissions and the duration of time that SRM is deployed.

“The primary control over the magnitude of the large temperature increases after an SRM shutoff is the background greenhouse gas concentrations. Thus, the greater the future emissions of greenhouse gases, the larger the temperature increases would be, and, similarly, the later the termination occurs while GHG emissions continue, the larger the temperature increases,” continued McCusker.

“The only way to avoid creating the risk of substantial temperature increases through SRM, therefore, is concurrent strong reductions of GHG emissions.”

Scientists solve a 14,000-year-old ocean mystery

At the end of the last Ice Age, as the world began to warm, a swath of the North Pacific Ocean came to life. During a brief pulse of biological productivity 14,000 years ago, this stretch of the sea teemed with phytoplankton, amoeba-like foraminifera and other tiny creatures, who thrived in large numbers until the productivity ended-as mysteriously as it began-just a few hundred years later.

Researchers have hypothesized that iron sparked this surge of ocean life, but a new study led by Woods Hole Oceanographic Institution (WHOI) scientists and colleagues at the University of Bristol (UK), the University of Bergen (Norway), Williams College and the Lamont Doherty Earth Observatory of Columbia University suggests iron may not have played an important role after all, at least in some settings. The study, published in the journal Nature Geoscience, determines that a different mechanism-a transient “perfect storm” of nutrients and light-spurred life in the post-Ice Age Pacific. Its findings resolve conflicting ideas about the relationship between iron and biological productivity during this time period in the North Pacific-with potential implications for geo-engineering efforts to curb climate change by seeding the ocean with iron.

“A lot of people have put a lot of faith into iron-and, in fact, as a modern ocean chemist, I’ve built my career on the importance of iron-but it may not always have been as important as we think,” says WHOI Associate Scientist Phoebe Lam, a co-author of the study.

Because iron is known to cause blooms of biological activity in today’s North Pacific Ocean, researchers have assumed it played a key role in the past as well. They have hypothesized that as Ice Age glaciers began to melt and sea levels rose, they submerged the surrounding continental shelf, washing iron into the rising sea and setting off a burst of life.

Past studies using sediment cores-long cylinders drilled into the ocean floor that offer scientists a look back through time at what has accumulated there-have repeatedly found evidence of this burst, in the form of a layer of increased opal and calcium carbonate, the materials that made up phytoplankton and foraminifera shells. But no one had searched the fossil record specifically for signs that iron from the continental shelf played a part in the bloom.

Lam and an international team of colleagues revisited the sediment core data to directly test this hypothesis. They sampled GGC-37, a core taken from a site near Russia’s Kamchatka Peninsula, about every 5 centimeters, moving back through time to before the biological bloom began. Then they analyzed the chemical composition of their samples, measuring the relative abundance of the isotopes of the elements neodymium and strontium in the sample, which indicates which variant of iron was present. The isotope abundance ratios were a particularly important clue, because they could reveal where the iron came from-one variant pointed to iron from the ancient Loess Plateau of northern China, a frequent source of iron-rich dust in the northwest Pacific, while another suggested the younger, more volcanic continental shelf was the iron source.

What the researchers found surprised them.

“We saw the flux of iron was really high during glacial times, and that it dropped during deglaciation,” Lam says. “We didn’t see any evidence of a pulse of iron right before this productivity peak.”

The iron the researchers did find during glacial times appeared to be supplemented by a third source, possibly in the Bering Sea area, but it didn’t have a significant effect on the productivity peak. Instead, the data suggest that iron levels were declining when the peak began.

Based on the sediment record, the researchers propose a different cause for the peak: a chain of events that created ideal conditions for sea life to briefly flourish. The changing climate triggered deep mixing in the North Pacific ocean, which stirred nutrients that the tiny plankton depend on up into the sea’s surface layers, but in doing so also mixed the plankton into deep, dark waters, where light for photosynthesis was too scarce for them to thrive. Then a pulse of freshwater from melting glaciers-evidenced by a change in the amount of a certain oxygen isotope in the foraminifera shells found in the core-stopped the mixing, trapping the phytoplankton and other small creatures in a thin, bright, nutrient-rich top layer of ocean. With greater exposure to light and nutrients, and iron levels that were still relatively high, the creatures flourished.

“We think that ultimately this is what caused the productivity peak-that all these things happened all at once,” Lam says. “And it was a transient thing, because the iron continued to drop and eventually the nutrients ran out.”

The study’s findings disprove that iron caused this ancient bloom, but they also raise questions about a very modern idea. Some scientists have proposed seeding the world’s oceans with iron to trigger phytoplankton blooms that could trap some of the atmosphere’s carbon dioxide and help stall climate change. This idea, sometimes referred to as the “Iron Hypothesis,” has met with considerable controversy, but scientific evidence of its potential effectiveness to sequester carbon and its impact on ocean life has been mixed.

“This study shows how there are multiple controls on ocean phytoplankton blooms, not just iron,” says Ken Buesseler, a WHOI marine chemist who led a workshop in 2007 to discuss modern iron fertilization. “Certainly before we think about adding iron to the ocean to sequester carbon as a geoengineering tool, we should encourage studies like this of natural systems where the conditions of adding iron, or not, on longer and larger time scales have already been done for us and we can study the consequences.”

Researchers analyze ‘rock dissolving’ method of geoengineering

The benefits and side effects of dissolving particles in our ocean’s surfaces to increase the marine uptake of carbon dioxide (CO2), and therefore reduce the excess amount of it in the atmosphere, have been analyzed in a new study published today.

The study, published today, 22 January, in IOP Publishing’s journal Environmental Research Letters, assesses the impact of dissolving the naturally occurring mineral olivine and calculates how effective this approach would be in reducing atmospheric CO2.

The researchers, from the Alfred Wegener Institute for Polar and Marine Research in Bremerhaven, Germany, calculate that if three gigatonnes of olivine were deposited into the oceans each year, it could compensate for only around nine per cent of present day anthropogenic CO2 emissions.

This long discussed ‘quick fix’ method of geoengineering is not without environmental drawbacks; the particles would have to be ground down to very small sizes (around one micrometre) in order to be effective. The grinding process would consume energy and therefore emit varying amounts of CO2, depending on the sort of power plants used to provide the energy.

Lead author of the study Peter Köhler said: “Our literature-based estimates on the energy costs of grinding olivine to such a small size suggest that with present day technology, around 30 per cent of the CO2 taken out of the atmosphere and absorbed by the oceans would be re-emitted by the grinding process.”

The researchers used a computer model to assess the impact of six different olivine dissolution scenarios. Olivine is an abundant magnesium-silicate found beneath the Earth’s surface that weathers quickly when exposed to water and air – in its natural environment it is dissolved by carbonic acid which is formed from CO2 out of the atmosphere and rain water.

If olivine is distributed onto the ocean’s surface, it begins to dissolve and subsequently increases the alkalinity of the water. This raises the uptake capacity of the ocean for CO2, which is taken up via gas exchange from the atmosphere.

According to the study, 92 per cent of the CO2 taken up by the oceans would be caused by changes in the chemical make-up of the water, whilst the remaining uptake would be down to changes in marine life through a process known as ocean fertilisation.

Ocean fertilisation involves providing phytoplankton with essential nutrients to encourage its growth. The increased numbers of phytoplankton use CO2 to grow, and then when it dies it sinks to the ocean floor taking the CO2 with it.

“In our study we only examined the effects of silicate in olivine. Silicate is a limiting nutrient for diatoms – a specific class of phytoplankton. We simulated with our model that the added input of silicate would shift the species composition within phytoplankton towards diatoms.

“It is likely that iron and other trace metals will also impact marine life if olivine is used on a large scale. Therefore, this approach can also be considered as an ocean fertilisation experiment and these impacts should be taken into consideration when assessing the pros and cons of olivine dissolution,” continued Köhler.

The researchers also investigated whether the deposition of olivine could counteract the problem of ocean acidification, which continues to have a profound effect on marine life. They calculate that about 40 gigatonnes of olivine would need to be dissolved annually to fully counteract today’s anthropogenic CO2 emissions.

“If this method of geoengineering was deployed, we would need an industry the size of the present day coal industry to obtain the necessary amounts of olivine. To distribute this, we estimate that 100 dedicated large ships with a commitment to distribute one gigatonne of olivine per year would be needed.

“Taking all our conclusions together – mainly the energy costs of the processing line and the projected potential impact on marine biology – we assess this approach as rather inefficient. It certainly is not a simple solution against the global warming problem.” said Köhler.

Improving effectiveness of solar geoengineering

Solar radiation management is a type of geoengineering that would manipulate the climate in order to reduce the impact of global warming caused by greenhouse gasses. Ideas include increasing the amount of aerosols in the stratosphere, which could scatter incoming solar light away from Earth’s surface, or creating low-altitude marine clouds to reflect these same rays.

Research models have indicated that the climatic effect of this type of geoengineering will vary by region, because the climate systems respond differently to the reflecting substances than they do to the atmospheric carbon dioxide that traps warmth in Earth’s atmosphere. New work from a team including Carnegie’s Ken Caldeira uses a climate model to look at maximizing the effectiveness of solar radiation management techniques. Their work is published October 21st by Nature Climate Change.

Attempting to counteract the warming effect of greenhouse gases with a uniform layer of aerosols in the stratosphere, would cool the tropics much more than it affects polar areas. Greenhouse gases tend to suppress precipitation and an offsetting reduction in amount of sunlight absorbed by Earth would not restore this precipitation. Both greenhouse gases and aerosols affect the distribution of heat and rain on this planet, but they change temperature and precipitation in different ways in different places. Varying the amount of sunlight deflected away from the Earth both regionally and seasonally could combat some of this problem.

By tailoring geoengineering efforts by region and by need, the team-led by California Institute of Technology’s Douglas MacMartin-was able to explore ways to maximize effectiveness while minimizing the side effects and risks of this type of planetary intervention.

“These results indicate that varying geoengineering efforts by region and over different periods of time could potentially improve the effectiveness of solar geoengineering and reduce climate impacts in at-risk areas,” Caldeira said. “For example, these approaches may be able to reverse long-term changes in the Arctic sea ice.”

The study used a sophisticated climate model, but the team’s model is still much simpler than the real world. Interference in Earth’s climate system, whether intentional or unintentional, is likely to produce unanticipated outcomes.

“We have to expect the unexpected,” Caldeira added. “The safest way to reduce climate risk is to reduce greenhouse gas emissions.”

Injecting sulfate particles into stratosphere won’t fully offset climate change

A polar bear walks along an expanse of open water at the edge of Hudson Bay near Churchill, Manitoba, in 2011.  The bears need pack ice to hunt for food, primarily seals, but climate change brings open water more often than it used to. Polar bears have been listed as a threatened species. -  Cecilia Bitz/U. of Washington
A polar bear walks along an expanse of open water at the edge of Hudson Bay near Churchill, Manitoba, in 2011. The bears need pack ice to hunt for food, primarily seals, but climate change brings open water more often than it used to. Polar bears have been listed as a threatened species. – Cecilia Bitz/U. of Washington

As the reality and the impact of climate warming have become clearer in the last decade, researchers have looked for possible engineering solutions – such as removing carbon dioxide from the atmosphere or directing the sun’s heat away from Earth – to help offset rising temperatures.

New University of Washington research demonstrates that one suggested method, injecting sulfate particles into the stratosphere, would likely achieve only part of the desired effect, and could carry serious, if unintended, consequences.

The lower atmosphere already contains tiny sulfate and sea salt particles, called aerosols, that reflect energy from the sun into space. Some have suggested injecting sulfate particles directly into the stratosphere to enhance the effect, and also to reduce the rate of future warming that would result from continued increases in atmospheric carbon dioxide.

But a UW modeling study shows that sulfate particles in the stratosphere will not necessarily offset all the effects of future increases in atmospheric carbon dioxide.

Additionally, there still is likely to be significant warming in regions where climate change impacts originally prompted a desire for geoengineered solutions, said Kelly McCusker, a UW doctoral student in atmospheric sciences.

The modeling study shows that significant changes would still occur because even increased aerosol levels cannot balance changes in atmospheric and oceanic circulation brought on by higher levels of atmospheric carbon dioxide.

“There is no way to keep the climate the way it is now. Later this century, you would not be able to recreate present-day Earth just by adding sulfate aerosols to the atmosphere,” McCusker said.

She is lead author of a paper detailing the findings published online in December in the Journal of Climate. Coauthors are UW atmospheric sciences faculty David Battisti and Cecilia Bitz.

Using the National Center for Atmospheric Research’s Community Climate System Model version 3 and working at the Texas Advanced Computing Center, the researchers found that there would, in fact, be less overall warming with a combination of increased atmospheric aerosols and increased carbon dioxide than there would be with just increased carbon dioxide.

They also found that injecting sulfate particles into the atmosphere might even suppress temperature increases in the tropics enough to prevent serious food shortages and limit negative impacts on tropical organisms in the coming decades.

But temperature changes in polar regions could still be significant. Increased winter surface temperatures in northern Eurasia could have serious ramifications for Arctic marine mammals not equipped to adapt quickly to climate change. In Antarctic winters, changes in surface winds would also bring changes in ocean circulation with potentially significant consequences for ice sheets in West Antarctica.

Even with geoengineering, there still could be climate emergencies – such as melting ice sheets or loss of polar bear habitat – in the polar regions, the scientists concluded. They added that the odds of a “climate surprise” would be high because the uncertainties about the effects of geoengineering would be added to existing uncertainties about climate change.

Testing geoengineering

Solar radiation management is a class of theoretical concepts for manipulating the climate in order to reduce the risks of global warming caused by greenhouse gasses. But its potential effectiveness and risks are uncertain, and it is unclear whether tests could help narrow these uncertainties. A team composed of Caltech’s Doug MacMynowski, Carnegie’s Ken Caldeira and Ho-Jeong Shin, and Harvard’s David Keith used modeling to determine the type of testing that might be effective in the future. Their work has been published online by Energy and Environmental Science.

Ideas for solar radiation management include increasing the amount of aerosols in the stratosphere, which could scatter incoming solar heat away from Earth’s surface, or creating low-altitude marine clouds to reflect these same rays. Clearly the size of the scale and the intricacies of the many atmospheric and climate processes make testing these ideas difficult.

“While it is clearly premature to consider testing solar radiation management at a scale large enough to measure the climate response, it is not premature to understand what we can learn from such tests,” said Doug MacMynowski of the California Institute of Technology, who led the research. “But we did not address other important questions such as the necessary testing technology and the social and political implications of such tests.”

Using models the team was able to demonstrate that smaller-scale tests of solar radiation management could help inform decisions about larger scale deployments. Short-term tests would be particularly effective at understanding the effects of geoengineering on fast-acting climate dynamics. But testing would require several decades and, even then, would need to be extrapolated out to the centuries-long time scales relevant to studying climate change.

Some scientists have theorized that volcanic eruptions could stand in for tests, as they would cause same types of atmospheric changes as aerosols. But they wouldn’t be as effective as a sustained test.

“No test can tell us everything we might want to know, but tests could tell us some things we would like to know,” Caldeira said. “Tests could improve our understanding of likely consequences of intentional interference in the climate system and could also improve our knowledge about the climate’s response to the interference caused by our carbon dioxide emissions.”

He added: “We conducted a scientific investigation into what might be learned by testing these proposals. We are not advocating that such tests should actually be undertaken,”

Biogeochemistry at the core of global environmental solutions

In the pursuit of food and fuel, humans are disrupting Earth's biogeochemical cycles. -
In the pursuit of food and fuel, humans are disrupting Earth’s biogeochemical cycles. –

If society wants to address big picture environmental problems, like global climate change, acid rain, and coastal dead zones, we need to pay closer attention to the Earth’s coupled biogeochemical cycles. So reports a special issue of Frontiers in Ecology and the Environment, published this month by the Ecological Society of America.

“There are nearly seven billion people on the planet. And our activities are throwing the Earth’s biogeochemical cycles out of sync, to the detriment of air and water resources, climate stability, and human health,” comments Dr. Jonathan J. Cole, a limnologist at the Cary Institute of Ecosystem Studies and co-editor of the special issue.

A biogeochemical cycle is a pathway by which a chemical element, such as carbon, moves through Earth’s biosphere, atmosphere, hydrosphere, and lithosphere. Some thirty cycles govern the composition of our environment, among them carbon, nitrogen, oxygen, and phosphorus.

Historically, biogeochemical cycles have been studied individually. But in the natural world, element cycles are intimately tied to one another, and seemingly small perturbations can have large impacts across cycles.

The Frontiers issue puts forth a new framework for understanding the biological, geological, and chemical processes that shape element cycles, and the ways in which they are coupled to one another.

It represents one of the first efforts to convene atmospheric scientists and ecologists on the topic. In addition to Cole, it was edited by Drs. Adrien C. Finzi of Boston University and Elisabeth A. Holland of the National Center for Atmospheric Research.

Dr. William H. Schlesinger, president of the Cary Institute and a contributor, notes, “The coupled biogeochemical cycle framework not only explains the causes of many of today’s leading environmental problems, it provides a road map for finding solutions at the global scale.”

Consider the connection between farms and fish. In the U.S., two-thirds of our estuaries are degraded by nitrogen and phosphorus pollution, which is often a by-product of agriculture. Livestock waste and crop fertilizer make their way into coastal waterways, where they stimulate algal blooms that strip oxygen from deep waters, degrade sensitive habitat, and ultimately kill fish.

A better understanding of how nitrogen, phosphorus, and oxygen cycles interact could help balance agricultural needs with the health and productivity of estuaries.

Coupled-cycles can also strengthen our ability to predict and manage climate change. Forests play a role in removing carbon dioxide from the atmosphere. A forest’s ability to sequester atmospheric carbon-an attribute that helps minimize climate change-is tied to nitrogen, phosphorus, and water availability. Yet current global climate models don’t incorporate these couplings in realistic ways.

An integrated view could provide a more accurate view of forest carbon sequestration limits, while helping to guide sustainable forestry practices.

Dr. Finzi concludes, “We are at a turning point. From satellite imagery to real-time environmental monitoring, we have the technology needed to reveal how coupled biogeochemical cycles shape the world and how our actions disrupt them. Now we need to focus on integrating data across observational and experimental networks and applying insights to management decisions.”