Science News, the Washington Post, and Climate Central have all written about a new study, published this week by the Proceedings of the National Academy of Sciences, that suggests a decade-long lull in global warming, which has caused some commentators to question the scientific underpinnings of climate change, stems from large increases in sulfur dioxide emissions in Asia. Between 2003 and 2007, global sulfur emissions have gone up by 26 percent. In the same period, Chinese sulfur dioxide emissions have doubled.
While burning coal is best known for emitting carbondioxide, a greenhouse gas, the sulfur dioxide the same process generates leads to the formation ofreflective sulfate particles that have the opposite effect on the climate. Releasing sulfates might seem, then, like a reasonable way to counteract global warming, but there’s a catch. Sulfates also cause acid rain and health problems. The World Health Organization estimates that air pollution, including sulfates, causes as many as 2 million premature deaths each year.
The combination of the contradictory coal burning impacts leaves policy makers in a bind: clean up the sulfates and accelerate the pace of global warming or allow sulfates to build up and people will die directly of air pollution. Reducing sulfate is relatively cheap and the health benefits don’t take long to realize, so most industrialized countries end up adopting pollution controls that reduce sulfate emissions. The United States, as well as industrialized European countries and Japan, cut sulfate emissions significantly in the 1970s and 1980s, and there’s little reason to believe that China will follow a different path.
In fact, the Chinese government is already in the midst of an effort to reduce sulfate pollution. A team of researchers, including NASA Goddard’s Mian Chin, used satellite imagery and other data about emissions to estimate sulfate emission trends in China in a 2010 paper published in Atmospheric Chemistry and Physics They found that sulfur dioxide emissions increased dramatically between 2000 and 2005, particularly in Northern China. But they also found that sulfur dioxide emissions in China, which I wrote about in an earlier post, began to decline in 2006 after the government began installing large numbers of flue-gas desulfurization (FGD) devices in coal power plants.
What does it all mean for the climate? In 2010, Drew Shindell and Greg Faluvegi of NASA’s Goddard Institute for Space Studies simulated a number of emission scenarios for China and India to find out. They looked, for example, at how the climate would respond if the Chinese and Indian economies continue to expand rapidly or only grow at a moderate pace. Likewise, they modeled what would happen if China and India instituted sulfate pollution controls immediately or waited a number of decades before doing so.
In their paper, Shindell and Faluvegi present their results, shown in the line graph at the beginning of this post, as a suite of projections. The strength of warming predicted depends on whether the economies continue to grow quickly and whether sulfate pollution slows, but there is one common – and concerning – similarity between all of the projections: regardless of how fast China or India grow or put off sulfate pollution controls, it’s not enough to mask warming from carbon dioxide in the long term, particularly in the mid-latitudes of the Northern Hemisphere where the climate impacts of sulfates from Asia are the most noticeable.
Here’s how the GISS authors explained the situation:
We find that while the near-term effect of air quality pollutants is to mask warming by CO2, leading to a net overall near-term cooling effect, this does not imply that warming will not eventually take place. Worldwide application of pollution control technology in use in Western developed countries and Japan along with continued CO2 emissions would lead to strong positive forcing in the long term irrespective of whether the pollution controls are applied immediately or several decades from now. Continued emissions at current (year 2000) pollutant and CO2 levels may have little near-term effect on climate, but the climate ‘debt’ from CO2 forcing will continue to mount. Once pollution controls are put into place as society demands cleaner air it will rapidly come due, leading to a “double warming” effect as simultaneous reductions in sulfate and increases in CO2 combine to accelerate global warming. The only way to avoid this would be not to impose pollution controls and to perpetually increase sulfur-dioxide emissions, which would lead to a staggering cost in human health and is clearly unsustainable.
Have you ever stopped to wonder why urban air can taste like singed rubber one day and crisp mountain air the next? Or what happens to all those delectable clouds of who-knows-what flowing from factory smokestacks and vehicle tailpipes? Or what makes a blanket of dense smog shroud a city skyline on certain days?
Raymond Hoff, an air pollution expert based at the University of Maryland, Baltimore County, sure has. Hoff has studied air pollution for more than three decades researching topics ranging from Arctic haze, to ozone-damaged beans on the banks of Lake Ontario, to the river of fumes that emanate from Interstate 95. He’s authored dozens of journal articles and book chapters, uses lasers to measure air pollutants, edits a blog about smog, 
and has led or participated in nearly two-dozen field experiments around the world.
We caught up with Hoff to find out more about his involvement in a new project – a NASA-sponsored aircraft campaign called DISCOVER-AQ – that will help fill in gaps between satellite measurements of pollution and data from ground-based stations. As part of the campaign, NASA will fly a large aircraft – a 117-foot P-3B – on low-altitude flights near major roadways.
What is your role in DISCOVER-AQ?
I manage a ground site at the University of Maryland, Baltimore County (UMBC) that will be part of the campaign. At UMBC, we use lidar, a type of laser, to create vertical profiles of pollutants in the atmosphere. We plan to make lidar measurements at the same time that NASA satellites and aircraft fly overhead and measure pollution from above. The idea is that the ground stations will help validate the satellite and aircraft measurements and give us a more accurate three-dimensional view of air pollution.
What are the main pollutants that you’ll be focusing on during the campaign?
In the summer in Baltimore, there are two pollutants of importance – ozone and particulate matter. Both can cause health problems. On bad air days, we see increases in the number of asthma incidents, cardiopulmonary problems, and heart attacks.
Baltimore skyline on a clear day. Baltimore skyline on a hazy day.
Where does ozone come from?
Sunlight reacts with certain pollutants – such as nitrogen dioxide, formaldehyde, and other volatile pollutants – in a long chain of reactions to produce ozone. Combustion engines, power plants, gasoline vapors and chemical solvents are key sources of the precursor gases.
What about particulate matter?
There’s a range of particulate in the air. In Baltimore, about 30 to 60 percent of the mass of particles in the air that we worry about are sulfates – small particles generated by emissions of sulfur dioxide. Coal-burning power plants, smelters, industrial boilers and oil refineries release most sulfur dioxide. The other 30 to 60 percent, depending on the day, is usually organic particles. Organics come from vehicle exhaust, evaporating paints, and various commercial and industrial sources. Vegetation also produces a significant amount of organics. The remainder is usually a mixture of dust, sea salt and nitrates.
Is that a fairly typical mixture of pollutants?
Yes, for a large cities along the Mid-Atlantic and in the Northeast. There are certainly regional differences. There are fewer sulfates in California, for example, because they cleaned sulfur out of their fuels. You see more dust in the West, more organics in the Southeast. You see high levels of certain industrial pollutants over cities like Houston where you have a robust petrochemical industry.
Is most of Baltimore’s pollution local or does it blow in from elsewhere?
We think about half of it comes in from the west over the Appalachians. Some of it comes up from Washington, and some, of course, is local.
Tell me something interesting about air quality in Baltimore.
The role of the Chesapeake Bay and the “bay breezes” are worth mentioning. If you have an urban area right next to a body of water, like we do with the Chesapeake, you have the sun beating down creating very hot surfaces and upward transport that produces winds that circulate air between the water and the land. If you’ve been down to the beaches in the summer, you’ve probably noticed that there’s often a breeze coming off the water during the day. At night, it’s the opposite. Polluted air flows off the land and pools over the water.
Isn’t it good that polluted air pools up over the water rather than the city at night?
Not really because it comes back over land the next afternoon. There are actually Maryland Department of the Environment monitoring sites up at the top of the Bay that get higher concentrations than anywhere else in the state because of the bay breezes and the way the wind flow pinches at the top of the Bay. For example, the monitoring station at Edgewood, which is about 20 miles northeast of downtown Baltimore, tends to get hit particularly hard by bay breezes. DISCOVER-AQ is going to fly aircraft in that area, and the campaign should help us understand the full three-dimensional spatial picture over the Bay.
I’ve heard that the highest pollution levels can actually occur in the suburbs instead of directly over a city core. True?
That’s true for certain pollutants, like ozone. Ozone requires nitrogen dioxide, organic compounds, and sunlight to form. However, the process doesn’t happen immediately. It takes a few hours for the air to stew enough for ozone to form. When the wind is blowing through an urban area you can have your highest concentration of ozone downwind of a city by 20 to 30 miles.
Meaning rural landscapes don’t necessarily have pristine air?
No. In fact, farms in rural areas downwind of cities can have problems with ozone because ozone damages plant health as well as human health. Beans, for example, are highly sensitive. If ozone levels get too high, they start to get brown blotches on their leaves.
I know there are networks of ground-based sensors to measure ozone near the surface. Is it possible to measure ozone from space?
A spaceborne measurement of ozone at the ground would be a great thing, but it is still a real challenge. Much of the ozone we have on the planet is high in the atmosphere in a layer of air called the stratosphere. It’s about 15 miles up, and it’s hard to see through the stratosphere with satellite instruments because it is so thick. You could say getting a good ozone measurement is a holy grail right now for NASA and the air quality research community. We’re hoping that DISCOVER-AQ will get us closer.
Aircraft will also be flying over highways during the campaign. Why?
We know that transportation is a major source of pollution in the Baltimore area. I-95 is a big transportation corridor, and one of the things we want to look at with DISCOVER-AQ is the nitrogen dioxide released by combustion engines. There are very few nitrogen dioxide ground instruments in the area, so we’re flying over the highways to see if we can pick out a signal. We’ve been able to start measuring nitrogen dioxide from space in the last few years, but we can improve those measurements by validating them with ground data.
Credit information. Text by Adam Voiland. Flight tracks visualization by the Scientific Visualization Studio. NASA P-3B shot available here. Baltimore hazy/clear comparison from CamNet. Sea breeze illustrations from NOAA. Ozone-damaged leaf shot available here.
On Earth Day, we published an interview about the “smog blog” created by Ray Hoff of the University of Maryland – Baltimore County. Today, we follow up by sharing this video, which has some striking shots of laser pulses from the instrument that Hoff’s atmospheric LIDAR group uses to take air quality measurements near Baltimore.
Plus, here are some outtakes from Hoff that did not fit into the original interview:
On the importance of satellites…
“We spend quite a bit of time trying to use satellite measurements as a surrogate for what we see on the ground because the Environmental Protection Agency can’t be everywhere. EPA has a thousand monitors in the United States, but those monitors are largely in urban areas, and they can be spaced quite far apart. There are, for example, no EPA samplers in Wyoming. NASA satellites can look everywhere.”
On why satellite measurements of aerosols are less accurate in the western U.S…
“In the West, the correlation between what happens on the ground is worse for two reasons. The land surface out in the western United States does not have as much vegetation, so it’s brighter and more difficult for NASA satellites to see the aerosols from space. The other thing is that there are a lot of fires in the West, which make it challenging to distinguish between aerosol types.”
On the challenges facing air quality researchers…
“One of the things they’d really like to have is better measurements of ozone at the ground level. Much of the ozone we have on the planet is in the stratosphere, about 20 kilometers or 15 miles up, and it’s hard to see through the ozone layer, since it’s so thick. We have to combine models with measurements from the ground and NASA airborne platforms, but the difficulty of seeing through this layer to surface ozone is kind of the holy grail of tropospheric air quality research right now.”
On geoengineering the climate with sulfate aerosols…
“A Nobel Prize winner has suggested putting more pollutants in the atmosphere in order to keep the planet cool. I actually think that’s a rather poor experiment for us to be trying with so little knowledge of how the atmosphere works. Humans have a pretty bad record of trying to “fix the planet.”
–Adam Voiland, NASA’s Earth Science News Team
Black carbon, the sooty particle that gives smoke from diesel engines and cooking fires a dark appearance, took center stage this week when Secretary of State Hillary Clinton attended a high-profile meeting of the Arctic Council in Nuuk, the capital of Greenland.
Black carbon has attracted the attention of climatologists and policy makers alike because its complex structure makes it so good at absorbing sunlight. To make this point, University of Illinois-based Tami Bond, one of the nation’s leading black carbon specialists, noted during a Congressional hearing last year that one ounce of black carbon dispersed in the atmosphere would block the amount of sunlight that would fall on a tennis court. The absorbed energy then gets transferred to the atmosphere as heat and contributes to global warming.
The Arctic Council meeting coincided with the release of two scientific reports focused on the cryosphere. The first, authored by the scientific arm of the Arctic Council, argued that the United Nations underestimated the rate at which the Arctic is losing sea ice and concluded the Arctic Ocean could be ice-free within the next thirty to forty years. The second makes the case that it’s possible to cut Arctic ice loss significantly by curbing black carbon emissions.
I’ve written before about the possibility that reducing black carbon emissions could save Arctic Sea ice. Recent modeling, conducted by Stanford’s Mark Jacobson and funded in-part by NASA, suggests that eliminating soot emissions from fossil fuel and biofuel burning over the next fifteen years could reduce Arctic warming by up to 1.7 °C (3 °F). (Net warming in the Arctic, in comparison, has been about 2.5 °C (4.5 °F) over the last century.
Future emissions aside, what has actually been happening with black carbon deposition trends in the Arctic? Have black carbon emissions, like carbon dioxide emissions, been going steadily up in recent decades?
A recent report, authored by climatologists at NASA’s Goddard Institute for Space Studies, offers a nice overview that I’ve excerpted below. It may come as a surprise that the amount of black carbon winds are dumping on Arctic ice has actually fallen over the last few decades. From the GISS study:
Recently there has been concern about impacts of black carbon on snow albedo in the Arctic and whether that has contributed to melting of Arctic sea-ice and snow. Some studies have focused on changes in Arctic BC since the 1980s when measurements were first made. Sharma et al. (2004) found a 60% decrease in atmospheric black carbon at Alert between 1989 and 2002. Recent Arctic snow measurements (e.g. Grenfell et al., 2009; Hegg et al., 2009) found BC concentrations to be about 5-15 ng g−1 in Canada, Alaska and the Arctic Ocean, about a factor of two lower than measured in the 1980s (e.g. Clarke and Noone, 1985). Contemporary Russian measurements are larger than the western Arctic, ranging from about 15-80 ng g−1, while BC concentrations in the Barants and Kara seas were measured at about 15-25 ng g−1 (Grenfell et al., 2009; Hegg et al., 2009). The Greenland ice sheet has relatively very low BC levels, about 2-3 ng g−1, similar to the measurements in the 1980s (Grenfell et al., 2009).
Bond showed some particularly helpful graphs during her testimony last year that give long-term emission trends. According to Bond’s estimates, black carbon emissions peaked around the turn of the century when dirty cooking stoves were common.
She also has showed a good graph that shows the sectors that produce the most black carbon.
Text by Adam Voiland. Image of Pitufkin Glacier in Greenland from NASA’s IceBridge Mission. Graphs from Tami Bond.
Joe Witte filed this report from the media viewing site at Vandenberg Air Force Base shortly before the Aquarius satellite blasted successfully into space.
More than a dozen reporters from Argentina are either standing or slowly moving about trying to stay warm while waiting for the launch of the Aquarius satellite. The low cloud deck over Vandenberg Air Force Base in California puts a damper on their spirits after traveling all the way from South America to see a Delta II rocket quickly disappear on it’s way to an orbit 400 miles above the earth.
Curious to learn more about some of the areas highlighted? Here’s a list of what, to me, at least, are eye-popping shots of some of the same places as seen by instruments aboard the many unmanned satellites that also orbit Earth.
The storms that recently sent a rash of tornadoes through the South have produced historic flooding along the Mississippi River. Over the weekend, the U.S. Army Corps of Engineers opened the Morganza Spillway in Louisiana for just the second time since buidling the structure in 1954.
Though the action will likely lessen damage in the major cities of New Orleans and Baton Rouge, opening the Morgananza will inundate thousands of square kilometers of land and displace between 30,000 and 60,000 people as spillover swells the Atchafalaya River.
The Atchafalaya, as the New Yorker’s John McPhee explains in masterly fashion in The Control of Nature, is on the verge of capturing the Mississippi’s flow. The Army Corps of Engineers diverts just 30 percent of the Mississippi’s water into the Atchafalaya, though the natural inclination of the Mississippi is to jump its banks and flow into the shorter and steeper Atchafalaya channel.
McPhee, in an essay that’s as relevant today as it when it was first published in 1987, describes the daunting challenge engineers face in trying to keep the Mississippi within its banks. It makes for sobering reading, but the essay makes an excellent complement to the series of satellite photos NASA’s Earth Observatory has released chronicling the flooding.
In the excerpt below, McPhee describes the Mississippi’s tendency to shift its course in swift and dramatic ways:
The Mississippi River, with its sand and silt, has created most of Louisiana, and it could not have done so by remaining in one channel. If it had, southern Louisiana would be a long narrow peninsula reaching into the Gulf of Mexico. Southern Louisiana exists in its present form because the Mississippi River has jumped here and there within an arc about two hundred miles wide, like a pianist playing with one hand—frequently and radically changing course, surging over the left or the right bank to go off in utterly new directions. Always it is the river’s purpose to get to the Gulf by the shortest and steepest gradient. As the mouth advances southward and the river lengthens, the gradient declines, the current slows, and sediment builds up the bed. Eventually, it builds up so much that the river spills to one side. Major shifts of that nature have tended to occur roughly once a millennium. The Mississippi’s main channel of three thousand years ago is now the quiet water of Bayou Teche, which mimics the shape of the Mississippi. Along Bayou Teche, on the high ground of ancient natural levees, are Jeanerette, Breaux Bridge, Broussard, Olivier—arcuate strings of Cajun towns. Eight hundred years before the birth of Christ, the channel was captured from the east. It shifted abruptly and flowed in that direction for about a thousand years. In the second century a.d., it was captured again, and taken south, by the now unprepossessing Bayou Lafourche, which, by the year 1000, was losing its hegemony to the river’s present course, through the region that would be known as Plaquemines. By the nineteen-fifties, the Mississippi River had advanced so far past New Orleans and out into the Gulf that it was about to shift again, and its offspring Atchafalaya was ready to receive it. By the route of the Atchafalaya, the distance across the delta plain was a hundred and forty-five miles—well under half the length of the route of the master stream.
For the Mississippi to make such a change was completely natural, but in the interval since the last shift Europeans had settled beside the river, a nation had developed, and the nation could not afford nature. The consequences of the Atchafalaya’s conquest of the Mississippi would include but not be limited to the demise of Baton Rouge and the virtual destruction of New Orleans. With its fresh water gone, its harbor a silt bar, its economy disconnected from inland commerce, New Orleans would turn into New Gomorrah. Moreover, there were so many big industries between the two cities that at night they made the river glow like a worm. As a result of settlement patterns, this reach of the Mississippi had long been known as “the German coast,” and now, with B. F. Goodrich, E. I. du Pont, Union Carbide, Reynolds Metals, Shell, Mobil, Texaco, Exxon, Monsanto, Uniroyal, Georgia-Pacific, Hydrocarbon Industries, Vulcan Materials, Nalco Chemical, Freeport Chemical, Dow Chemical, Allied Chemical, Stauffer Chemical, Hooker Chemicals, Rubicon Chemicals, American Petrofina—with an infrastructural concentration equalled in few other places—it was often called “the American Ruhr.” The industries were there because of the river. They had come for its navigational convenience and its fresh water. They would not, and could not, linger beside a tidal creek. For nature to take its course was simply unthinkable. The Sixth World War would do less damage to southern Louisiana. Nature, in this place, had become an enemy of the state.
Text by Adam Voiland. Photographs published originally by NASA’s Earth Observatory.
Between April 25 and April 28, a record-breaking total of 362 tornadoes tore through the southeastern and central United States. Could climate change fuel such an unprecedented cluster of twisters? A number of commentators have addressed the question, but the most concise answer I’ve heard yet comes in the 36th minute of an On Point interview with NOAA tornado expert Harold Brooks. [The bolding is mine.]
On Point: When you look at the architecture of the weather that produced these storms can you tie it to global climate change? We’ve seen warning after warning saying that we may see an increase in storm conditions because of climate change.
Brooks: Well, the planet has undoubtedly warmed in the last 50 to 100 years. And it will undoubtedly continue to warm as greenhouse gases play a greater role. It’s not really clear what the connection is between tornadoes [and climate change] in particular. Some of the ingredients we look for in the production of supercells, such as the warm moist air at low levels, are going to increase in intensity and frequency and be supportive of supercell storms. On the other hand, one of the main predictions of climate change is that the equator to pole temperature difference will decrease because the poles will warm more than the equator. That’s related to the change of the winds with height term, which is one of the things that helps organize storms and make them more likely to produce tornadoes. That’s predicted to lessen as we go along. So we’ve got some ingredients that will be increasing in intensity and some that will be decreasing. If we look historically at the record and try to make some adjustments over the last 50 years for what we know is changes in reporting, we really see no correlation between occurrence and intensity and global surface temperatures or even the US national temperature.
While scientists will surely continue to study this, one thing is quite certain: When tornadoes do come along, NASA will do all it can to track and monitor them and their aftermath using satellites and other assets. On May 2, 2011, for example, the NASA Earth Observatory reported that the Advanced Land Imager (ALI) on NASA’s Earth Observing-1 (EO-1) satellite captured the natural-color image above of a massive tornado’s destructive path through Tuscaloosa.
The trail of damage stretched 80.3 miles (129.2 kilometers) long and as much as 1.5 miles (2.4 kilometers) wide.The tan-toned, debris-filled path passes through the center of town, affecting both commercial and residential properties. The track passes south of Bryant Denny Stadium and just north of University Mall. The Tuscaloosa tornado caused more than 1,000 injuries and at least 65 deaths across several town and cities, the highest number of fatalities from a single tornado in the United States since May 25, 1955. –Adam Voiland
