Huntington Brings Becky Shaw to Boston
Comments(0) In the World: Nanotech on the farm
Comments(0) Cassava is a tropical root vegetable and staple crop for millions of people in sub-Saharan Africa. However, it’s tricky to handle: Once the root is removed from the ground, it spoils within one to three days, so farmers must get it to processing centers as soon as possible after harvesting it. If they don’t, the crop goes to waste.
A simple way to prolong cassava’s shelf life could help farmers avoid that waste and sell their crop beyond their local region. Paula Hammond, MIT professor of chemical engineering, and other scientists are now working on an innovative way to help them do that, using nanotechnology — technology that controls material at a molecular or atomic scale. Their idea is to design a plastic storage bag lined with nanoparticles that would react with oxygen, preventing the roots’ oxygen-induced rotting.
“That would enable farmers to harvest and store and process at times convenient to them,” says Hammond, who traveled to Kenya and Ghana last summer with an international group of scientists to meet with farmers and come up with new ways to improve agricultural efficiency.
It may seem odd to send Hammond, a chemical engineer who focuses on nanotechnology, into rural Africa to help farmers. But that’s exactly the point, says Todd Barker, a partner for the Meridian Institute, which organized the trip with funding from the Bill & Melinda Gates Foundation.
Organizers were looking for scientists who specialize in fields not traditionally involved in international development. And they wanted people who knew little or nothing about agriculture, says Barker. “We wanted to get them to look at these particular problems in Africa with a fresh set of eyes.”
‘An important problem’
After the Meridian Institute identified three agricultural chains where farmers needed help — cassava, dairy and maize (corn), Barker enlisted Jeffrey Carbeck PhD ’96, a chemical engineer and entrepreneur, to identify scientists who would fit in with the mission. “I was looking for people who had a deep technical background but had shown they could apply it in multiple areas,” says Carbeck, who knew Hammond from their graduate school days at MIT.
Carbeck thought that Hammond, an expert in designing polymers for drug delivery, sensors and energy, would fit perfectly. Hammond, in turn, was intrigued by the idea. “It sounded like such an important problem, and I had never been to Africa. This was a chance to see it from a very unique perspective,” she says.
Equipped with Land Rovers and digital video cameras, the group of a dozen scientists from around the world traveled to farms throughout the two African nations, talking with farmers to find out the biggest obstacles they face.
For Hammond, the trip was enlightening. “These working families have very immediate problems and have neither the resources, nor perhaps the voice, to express them to groups of elite scientists, and that’s what this allowed them to do,” she says. “These are really exciting problems outside the realm of what we might normally encounter in academia.”
The team found that dairy farmers have a similar problem to cassava farmers — getting their milk to processing centers before it spoils. Most farms don’t have their own refrigeration facilities, so the farmers have to carry their milk in plastic jugs, usually on foot or bicycle, to the nearest cooling center.
If the cooling centers are far from the farm, the farmers might make only one trip a day, so any milk produced after that trip is in danger of spoiling before the next day’s trip. Milk that goes bad is rejected at the center and dumped out.
To avoid that waste, Hammond and other scientists in the group came up with the idea to design a milk container with a nanopatterned, antimicrobial coating that would preserve milk longer than a plain plastic jug.
The African dairy farmers are also interested in a way to easily test their cows to see if they’re pregnant or in heat. Cows must be bred and produce calves in order to produce milk, but if a cow runs dry, it’s difficult to tell whether it’s due to lack of pregnancy or a common udder infection known as mastitis.
There is no simple test for cow pregnancy as there is for humans, but scientists who went on the trip came up with the idea to adapt existing nanopatterned paper sensors to detect bovine pregnancy.
The Gates Foundation originally planned to allocate funding for two or three ideas that came out of the trip, but there were so many (more than 200, later consolidated into 22 concepts), that the foundation is encouraging the scientists to pursue as many as possible. The Meridian Institute will initially focus on diagnostic tools for mastitis, the new milk container, tick-borne disease and other livestock diseases, safety tests for milk, a modified plastic tank for maize storage, and a new way to dry cassava.
The Meridian Institute is now working on starting up a foundation that would serve as an “incubator” to help develop, test and bring these ideas to commercialization, according to Barker. “The major challenge now is to make sure the ideas that came out of the trip reach the farmers in Africa,” he says.
In the World is a column that explores the ways members of the MIT community are developing technology — from the appropriately simple to the cutting edge — to help meet the needs of communities around the planet, especially those in the developing world.
Wind resistance
Comments(0) Wind power has emerged as a viable renewable energy source in recent years — one that proponents say could lessen the threat of global warming. Although the American Wind Energy Association estimates that only about 2 percent of U.S. electricity is currently generated from wind turbines, the U.S. Department of Energy has said that wind power could account for a fifth of the nation’s electricity supply by 2030.
But a new MIT analysis may serve to temper enthusiasm about wind power, at least at very large scales. Ron Prinn, TEPCO Professor of Atmospheric Science, and principal research scientist Chien Wang of the Department of Earth, Atmospheric and Planetary Sciences, used a climate model to analyze the effects of millions of wind turbines that would need to be installed across vast stretches of land and ocean to generate wind power on a global scale. Such a massive deployment could indeed impact the climate, they found, though not necessarily with the desired outcome.
In a paper published online Feb. 22 in Atmospheric Chemistry and Physics, Wang and Prinn suggest that using wind turbines to meet 10 percent of global energy demand in 2100 could cause temperatures to rise by one degree Celsius in the regions on land where the wind farms are installed, including a smaller increase in areas beyond those regions. Their analysis indicates the opposite result for wind turbines installed in water: a drop in temperatures by one degree Celsius over those regions. The researchers also suggest that the intermittency of wind power could require significant and costly backup options, such as natural gas-fired power plants.
Prinn cautioned against interpreting the study as an argument against wind power, urging that it be used to guide future research that explores the downsides of large-scale wind power before significant resources are invested to build vast wind farms. “We’re not pessimistic about wind,” he said. “We haven’t absolutely proven this effect, and we’d rather see that people do further research.”
Daniel Kirk-Davidoff, a chief scientist for MDA Federal Inc., which develops remote sensing technologies, and adjunct professor of meteorology at the University of Maryland, has examined the climate impacts of large-scale wind farms in previous studies. To him, the most promising result of the MIT analysis is that it indicates that the large-scale installation of wind turbines doesn’t appear to slow wind flow so much that it would be impossible to generate a desirable amount of energy. “When you put the wind turbines in, they are generating the kind of power you’d hope for,” he said.
Tapping the wind resource
Previous studies have predicted that annual world energy demand will increase from 14 terawatts (trillion watts) in 2002 to 44 terawatts by 2100. In their analysis, Prinn and Wang focus on the impact of using wind turbines to generate five terawatts of electric power.
Using a climate model developed by the U.S. National Center for Atmospheric Research, the researchers simulated the aerodynamic effects of large-scale wind farms — located both on land and on the ocean — to analyze how the atmosphere, ocean and land would respond over a 60-year span.
For the land analysis, they simulated the effects of wind farms by using data about how objects similar to turbines, such as undulating hills and clumps of trees, affect surface “roughness,” or friction that can disturb wind flow. After adding this data to the model, the researchers observed that the surface air temperature over the wind farm regions increased by about one degree Celsius, which averages out to an increase of .15 degrees Celsius over the entire global surface.
According to Prinn and Wang, this temperature increase occurs because the wind turbines affect two processes that play critical roles in determining surface temperature and atmospheric circulation: vertical turbulent motion and horizontal heat transport. Turbulent motion refers to the process by which heat and moisture are transferred from the land or ocean surface to the lower atmosphere. Horizontal heat transport is the process by which steady large-scale winds transport excessive heat away from warm regions, generally in a horizontal direction, and redistribute it to cooler regions. This process is critical for large-scale heat redistribution, whereas the effects of turbulent motion are generally more localized.
In the analysis, the wind turbines on land reduced wind speed, particularly on the downwind side of the wind farms, which reduced the strength of the turbulent motion and horizontal heat transport processes that move heat away from the Earth’s surface. This resulted in less heat being transported to the upper parts of the atmosphere, as well as to other regions farther away from the wind farms. The effect is similar to being at the beach on a windy summer day: If the wind weakened or disappeared, it would get warmer.
In contrast, when examining ocean-based wind farms, Prinn and Wang found that wind turbines cooled the surface by more than one degree Celsius. They said that these results are unreliable, however, because in their analysis, they modeled the effects of wind turbines by introducing surface friction in the form of large artificial waves. But they acknowledge that this is not an accurate comparison, meaning that a better way of simulating marine-based wind turbines must be developed before reliable conclusions can be made.
In addition to changes in temperatures and surface heat fluxes, they also observed changes in large-scale precipitation, particularly at the mid-latitudes in the Northern Hemisphere. Although these changes exceeded 10 percent in some areas, the global total changes were not very large, according to Prinn and Wang.
To investigate the effect of wind variability on the intermittency in wind power generation, the researchers used the climate model to estimate the monthly-mean wind power consumption and electrical generation for each continent, concluding that there are very large and geographically extensive seasonal variations, particularly over North and South America, Africa and the Middle East. They explain that this unreliability means that an electrical generation system with greatly increased use of wind turbines would still require backup generation even if continental-scale power lines enabled electrical transmission from windy to non-windy areas.
Although Prinn and Wang believe their results for the land-based wind farms are robust, Wang called their analysis a “proof-of-concept” study that requires additional theoretical and modeling work, as well as field experiments for complete verification.
Their next step is to address how to simulate ocean-based wind farms more accurately. They plan to collaborate with aeronautical engineers to develop parameters for the climate model that will allow them to simulate turbines in coastal waters.
Mr. Sloane Is Entertaining
Comments(0) A brashly provocative playwright whose short career in the 1960s included What the Butler Saw and Loot, Joe Orton weaves seduction, despair, and slapstick into his dark comedy Entertaining Mr. Sloane, the current production of the Publick Theatre Boston.
Sounds of War
Comments(0) With an eight-minute loop blaring around the clock, a dark room fills with a mélange of sounds: children giggling, a man singing in Arabic, helicopters hovering, guns firing, military leaders barking commands.
In a projected installation at the Institute of Contemporary Art Boston, …OUT OF HERE: The Veterans Project, Polish artist Krzysztof Wodiczko transports visitors to wartime Iraq through the expressions of soldiers and civilians.
Huntington Brings Becky Shaw to Boston
Comments(0) An open, collaborative space
Comments(0) The design of MIT’s new Media Lab building, which formally opened last week, is not only aesthetically pleasing, but also serves the interests of the lab’s own unique culture.
“It’s a building that very specifically was intended to support a particular kind of community and a particular research style,” explains William Mitchell, the Alexander W. Dreyfoos, Jr. (1954) Professor of Architecture and Professor of Media Arts and Sciences at MIT. Specifically, he says, it is intended to foster a serendipitous exchange of ideas among the “intensely cross-disciplinary” researchers by making the laboratory spaces exceptionally open, with broad and often surprising sight lines from one working space to another.
Cross-disciplinary research is a hallmark of MIT in general, but at the Media Lab, this gets carried to extremes. The lab features research teams working on projects that range from designing new artificial limbs to new banking systems, from cuddly, personable robots to new ways of storing and retrieving medical records, from educational electronic toys and computer languages to fanciful futuristic musical instruments.
The Media Lab, now celebrating its 25th anniversary, is part of MIT’s School of Architecture and Planning. The new complex will also house some of this school’s other departments, including a new Art, Culture and Technology Program.
The seven lab spaces that house various combinations of working groups were modeled after “the cube,” one of the laboratory spaces in the original I.M. Pei-designed Media Lab building (now connected to the new one on several floors). Each of these labs consists of a two-story-high open central workshop area, surrounded on two or three sides by offices that open onto a balcony overlooking the central space. All of these working spaces, in turn, are arrayed around a central atrium that spans five of the building’s six stories. The atrium is crisscrossed by ramps and stairways and also served by glass-enclosed elevators.
Open space
All of this open space lets in abundant natural light — a trademark of the architect, Japan’s Fumihiko Maki — while affording the occupants grand views of the Charles River and Boston skyline. To avoid excess heat in summertime, aluminum bars extend over much of the window area to filter the light.
The building also “reverses the traditional logic of the way you do academic buildings,” Mitchell says, by putting the public spaces on the top floor. “These become attractions that draw people up through the building,” he says, and then reward them with impressive views. And as visitors ascend through the central space, they have open views into lab spaces; this “puts the building on display, to make the work of the various groups in the Media Lab visible,” Mitchell says.
“This is important,” he adds, “because you can’t have effective cross-disciplinary work unless you can see what other people are doing.” That approach, he says, is “an absolutely radical departure from traditional MIT spaces.”
In some cases, the combinations of groups working together in the new lab spaces have obvious connections — for example, one lab now houses the Biomechatronics group developing prosthetic and ability-enhancing attachments for the human body, the New Media Medicine group, which is developing new ways of collecting, storing and retrieving medical data, and the Affective Computing group, which includes new robots designed to help teach interactive behavior to autistic children. Other combinations are a bit more surprising, such as the pairing of Mitchell’s Smart Cities group, which is developing a variety of foldable, stackable electric vehicles, with composer Tod Machover’s Opera of the Future group and its collection of high-tech musical instruments.
Andrew Lippman, co-director of MIT’s Communications Futures Program at the Media Lab, says the original building was designed to foster such collaborative research, and “the new building does that in spades. It raises the stakes.” The openness of the building, he says, “allows you to open your thinking.” The open atrium with its views into all the different lab spaces means that “you can stand there and literally feel the hum of what goes on. So the physical design will contribute to the style of the work that goes on there. I hope what will happen is that the space will enhance the opportunities for collaboration and cross-fertilization.”
But some of the building’s features are decidedly retro for a hotbed of new, cutting-edge technology. For example, all the offices have windows that can be opened for ventilation. Mitchell says this “makes the control systems a lot more complicated” for heating and cooling, but is worth it because it’s something that makes a big difference to people. “If you build a building around specific technology, it’ll be obsolete quickly. But fundamental human attitudes haven’t changed.” The new building doesn’t incorporate much in the way of specific new technology, but is designed to allow for experimentation with new electronics and communications systems.
But it is still the Media Lab. There will be “an information architecture that mirrors the accessibility and openness embodied in the architecture,” Lippman says. For example, there will be display stations strategically placed around the building and in the labs, partly to provide information about what’s going on “to optimize the experience of a visitor.”
While many labs or businesses may have systems designed to display details of projects in progress for the use of their own people, he says, “that doesn’t necessarily reflect what anyone else in the world is interested in.” At the Media Lab, “by optimizing the systems both for ourselves and for sponsors and guests and families,” he says, these systems “will become a part of the culture of this place.” The displays will “give you a window into what’s going on in the labs and where your colleagues are, and you can communicate with them with just a gesture.”
For example, even things as simple as the signs on office doors will be electronic interactive displays. David Small, associate professor of media arts and sciences, is concentrating on the development of interactive displays in the lab. He says that if you arrive at his office for a meeting, instead of a printed sign that just gives his name, the display might say “Dave is upstairs, but he knows you have a meeting now and he’ll be right down” — and perhaps allow you to send him a text saying you’re there.
The development of these communication systems will be an ongoing part of the life of the lab, Lippman says. “It’s not going to hatch, it’s going to evolve.”
The display systems will also provide real-time data on the building’s lighting, heating and cooling systems. “We want to make the place a living laboratory for energy efficiency research,” Lippman says.
Small adds that these displays will show people “detailed information about real-time electrical usage. We’re interested in how you might use that to change people’s behavior.”
But most of all, the systems are designed to grow. Displays and controls are designed “to be as hackable as possible,” Small says, so that students can experiment with setting up different kinds of displays and interactive systems as technology develops.
Mitchell says the building really needs to be seen in person to be appreciated. “I think people are going to be astounded by the qualities of the interior space,” he says. Maki’s buildings tend not to be flashy on the outside, he says, but have interiors that provide “an explosion of space and lightness. There’s a ‘wow!’ moment when you go inside.”
3 Questions: David Miliband on Afghanistan’s future
Comments(0) As U.S.-led forces step up their military efforts in Afghanistan, British Foreign Secretary David Miliband has begun urging Afghan President Hamid Karzai and his government to push for a peace settlement with Taliban insurgents. Before delivering the Karl Taylor Compton Lecture on Wednesday, Miliband — who has an MA in political science from MIT — sat down with MIT News to discuss Afghanistan.
Q. You’re here to help try to spur a peace process forward in Afghanistan. You’ve met Hamid Karzai, you were at his inauguration along with other Western officials in November. At this time, does he have the legitimacy and stature to be central to a peace process and stable government?
A. Well, he’s the elected leader of Afghanistan, the elected president of Afghanistan. There were very serious allegation of fraud in respect to his election, but I don’t think many people doubt that he got more votes than his opponent, even though he didn’t get the 50 percent absolute majority in the first round. A recent poll by the BBC suggests he has quite a lot of support from the Afghan people, who believe him to be their elected president, legitimately elected president. So I think the answer to that has got to be, ‘Yes.’ He is the president of the country, and he has huge responsibilities. And we have to work with him.
Q. U.S. Secretary of Defense Robert Gates was just in Kabul, and said about possible negotiations, “The timing of this, really I think, in many respects depends on the conditions on the ground in terms of when people, particularly the more senior [Taliban] commanders, realize that the odds against their success are no longer in their favor.” To what extent is military success a precondition of diplomatic success, or to what extent, and for what reasons, can they co-exist at the same time?
A. Well, I think that military and civilian effort can together create the conditions for the political process. And the military effort now is significant, the philosophy is right, to protect the population, the numbers are right, in terms of the surge, the effort from the Pakistanis is right, in terms of what they’re doing on the Pakistan side of the border. So that means that it is the right time to have the sort of political drive that’s going to bring this insurgency to an end.
Q. Over the last several weeks we’ve seen concerted military action [by American and British forces] in Marjah. But there have been some temporary military successes in the Helmand Province before, which displaced Taliban leaders, who were then able to come back later. So what might make this time different?
A. Afghan capacity: capacity on security, through the Afghan national army and the Afghan national police; capacity in governance, through the support of provincial and district governments; and capacity for politics to emerge that brings disaffected Pashtuns who are not part of global jihad into the political process. That’s the difference. In the end, the population are the best protection against the insurgency. To make that possible, we’ve got to protect the population.
In MIT visit, Miliband presses for Afghan peace deal
Comments(0) British Foreign Secretary David Miliband on Wednesday urged the Afghanistan government to consider bringing Taliban supporters into its political system, telling an MIT audience that the prompt pursuit of a political deal among Afghanistan’s warring factions was necessary to build a lasting peace in that country.
“My argument today is that now is the time for the Afghans to pursue a political settlement with as much vigor and energy as we are pursuing the military and civilian effort,” said Miliband SM ’90, delivering the Karl Taylor Compton Lecture in Kresge Auditorium.
Miliband’s talk came as U.S. and British troops make a renewed push to secure the Taliban stronghold of Helmand Province in southern Afghanistan. The Western troops have been attempting to control the town of Marjah, and aim to secure the region’s major city, Kandahar, this summer.
While acknowledging the necessity of the military action, Miliband struck a different point of emphasis in his talk, stressing the importance of a simultaneous process of political reconciliation. “Afghanistan will never achieve a sustainable peace unless many more Afghans are inside the political system, and the neighbors [nearby countries] are onside with the political settlement,” said Miliband, whose Labour Party is expected to face a strong challenge from the opposition Conservatives in Britain’s forthcoming general election later this spring.
The lecture was intended in part to send a message to Afghan president Hamid Karzai, who has suggested his country hold a jirga in April — a kind of grand peace negotiation about the country’s political future. Western governments want to make clear to Karzai, re-elected in controversial circumstances in 2009, that they expect improvements in governance to accompany improvements in security.
“The international community will judge him by his actions, not his words,” Miliband warned on Wednesday, later adding, “The Afghans themselves must own, lead and drive such political engagement.”
Talking to the Taliban
Miliband’s speech laid out a framework for the “political outreach” that he thinks will be useful in reconstructing Afghanistan. As Miliband sees it, a sustainable Afghan government will need to be more inclusive of ethnic Pashtuns, who have often supported the Taliban; will need to decentralize and provide better support for regional governors and governing councils; should give parliament a greater voice in political affairs; and must address the pervasive problem of corruption in the Afghan government.
Adding these elements to the Afghan political system would mean supplementing the Bonn Agreement, the accords worked out after the successful capture of Kabul, Afghanistan’s capital, by the United States and its allies, following the Sept. 11, 2001, terrorist attacks. Those attacks were carried out by al-Qaida terrorists given protection and resources by the Taliban government in Afghanistan.
In turn, extending the tribal and ethnic scope of Afghanistan’s government would inevitably mean bringing former Taliban fighters or supporters into the fold. “The idea of political engagement with those who would directly or indirectly attack our troops is difficult,” Miliband acknowledged. However, he added, “dialogue is not appeasement and political space is not the same as veto power or domination.”
To be sure, Miliband said, he has no expectation that all militants would themselves be willing to participate in a process of reconciliation. “Some insurgents are committed to al-Qaida’s violent extremist agenda,” Miliband observed. “There will never be reconciliation with them — they must be beaten back.”
Upward trajectory in ‘two to five years’
A portion of Miliband’s lecture was devoted to acknowledging the complications of getting Afghanistan’s many neighbors to agree on a path forward for the country. Pakistan, the country regarded as having the most influence inside Afghanistan, “holds many of the keys to security and dialogue,” Miliband said. “It clearly has to be a partner in finding solutions in Afghanistan.”
Miliband noted that like other nations, “Pakistan will only act according to its own sense of its national interest.” That said, Miliband also said he believes there has been a “significant change” in Pakistan during the last 18 months under President Asif Ali Zardari, and he expressed optimism that countries with vested interests in Afghanistan — including India, Russia, Turkey and China — will recognize a basic fact about the region: “The status quo in Afghanistan hurts all.”
And Miliband did, at times, re-emphasize the importance of military progress to the possibility of civil reconstruction in the country. “Only if the scale of the insurgency itself is reduced will the Afghan authorities be able to govern their land in sustainable or acceptable ways,” he said. Fewer than half of regional governors even have an office; fewer than a quarter of them have electricity.
Still, Miliband suggested, if both military and political progress take place in 2010, then “within two to five years it is realistic to aspire to see a country on an upward trajectory, still poor but with a just peace, with democracy and inclusive politics bedding down at all levels and with incomes growing.”
After his talk, Miliband, who earned his master’s in political science from MIT, was presented a school ring onstage, from the Graduate Student Council. While on campus two decades ago, he remarked at the outset of his speech, “I would never have believed that I would be British Foreign Secretary in a Labour government explaining a war in Afghanistan.”
Explained: Radiative forcing
Comments(0) This is the first of a two-part “Explained” on the scientific concepts underlying the concept of the greenhouse effect and global climate change.
When people talk about global warming or the greenhouse effect, the main underlying scientific concept that describes the process is radiative forcing. And despite all the recent controversy over leaked emails and charges of poorly sourced references in the last Intergovernmental Panel on Climate Change report, the basic concept of radiative forcing is one on which scientists — whatever their views on global warming or the IPCC — all seem to agree. Disagreements come into play in determining the actual value of that number.
The concept of radiative forcing is fairly straightforward. Energy is constantly flowing into the atmosphere in the form of sunlight that always shines on half of the Earth’s surface. Some of this sunlight (about 30 percent) is reflected back to space and the rest is absorbed by the planet. And like any warm object sitting in cold surroundings — and space is a very cold place — some energy is always radiating back out into space as invisible infrared light. Subtract the energy flowing out from the energy flowing in, and if the number is anything other than zero, there has to be some warming (or cooling, if the number is negative) going on.
It’s as if you have a kettle full of water, which is at room temperature. That means everything is at equilibrium, and nothing will change except as small random variations. But light a fire under that kettle, and suddenly there will be more energy flowing into that water than radiating out, and the water is going to start getting hotter.
In short, radiative forcing is a direct measure of the amount that the Earth’s energy budget is out of balance.
For the Earth’s climate system, it turns out that the level where this imbalance can most meaningfully be measured is the boundary between the troposphere (the lowest level of the atmosphere) and the stratosphere (the very thin upper layer). For all practical purposes, where weather and climate are concerned, this boundary marks the top of the atmosphere.
While the concept is simple, the analysis required to figure out the actual value of this number for the Earth right now is much more complicated and difficult. Many different factors have an effect on this balancing act, and each has its own level of uncertainty and its own difficulties in being precisely measured. And the individual contributions to radiative forcing cannot simply be added together to get the total, because some of the factors overlap — for example, some different greenhouse gases absorb and emit at the same infrared wavelengths of radiation, so their combined warming effect is less than the sum of their individual effects.
In its most recent report in 2007, the IPCC produced the most comprehensive estimate to date of the overall radiative forcing affecting the Earth today. Ronald Prinn, the TEPCO Professor of Atmospheric Science and director of MIT’s Center for Global Change Science, was one of the lead authors of that chapter of the IPCC’s Fourth Assessment Report. Radiative forcing “was very small in the past, when global average temperatures were not rising or falling substantially,” he explains. For convenience, most researchers choose a “baseline” year before the beginning of world industrialization — usually either 1750 or 1850 — as the zero point, and compute radiative forcing in relation to that base. The IPCC uses 1750 as its base year and it is the changes in the various radiative forcing agents since then that are counted.
Thus radiative forcing, measured in watts per square meter of surface, is a direct measure of the impact that recent human activities — including not just greenhouse gases added to the air, but also the impact of deforestation, which changes the reflectivity of the surface — are having on changing the planet’s climate. However, this number also includes any natural effects that may also have changed during that time, such as changes in the sun’s output (which has produced a slight warming effect) and particles spewed into the atmosphere from volcanoes (which generally produce a very short-lived cooling effect, or negative forcing).
Although all of the factors that influence radiative forcing have uncertainties associated with them, one factor overwhelmingly affects the uncertainty: the effects of aerosols (small airborne particles) in the atmosphere. That’s because these effects are highly complex and often contradictory. For example, bright aerosols (like sulfates from coal-burning) are a cooling mechanism, whereas dark aerosols (like black carbon from diesel exhausts) lead to warming. Also, adding sulfate aerosols to clouds leads to smaller but more abundant droplets that increase cloud reflectivity, thus cooling the planet.
“The error bars in the greenhouse gas forcing are very small,” Prinn says. “The biggest uncertainty in defining radiative forcing comes from aerosols.”
So, given all these factors and their range of errors, what’s the answer? The current level of radiative forcing, according to the IPCC AR4, is 1.6 watts per square meter (with a range of uncertainty from 0.6 to 2.4). That may not sound like much, Prinn says, until you consider the total land area of the Earth and multiply it out, which gives a total warming effect of about 800 terawatts — more than 50 times the world’s average rate of energy consumption, which is currently about 15 terawatts.
Part two of this series will examine the concept of climate sensitivity, which determines how much the planet’s temperature will change due to a given radiative forcing.