NEWS
Chlorophyll fluorescence from crops can be detected, here by an aerial sensor called HyPlant.
REMOTE SENSING
Carbon-mapping satellite will monitor plants’ faint glow Launch of Orbiting Carbon Observatory-2 promises precise mapping of chlorophyll fluorescence from space
PHOTO: AIRBORNE SENSOR HYPLANT OF THE IBG-2/FORSCHUNGSZENTRUM JÜLICH/GERMANY
By Eric Hand
I
t’s a lesson learned in grade school: Sunlight falls on the leaf, and, catalyzed by chlorophyll, atmospheric carbon dioxide is absorbed and fixed inside a sugar molecule. But there’s also a startling extra credit factoid: The leaf re-emits 1% of that sunlight as a faint red glow. Plant physiologists have known about chlorophyll fluorescence for decades. However, the ability to map this weak signal from space, through the confounding murk of Earth’s atmosphere, has arrived only in the past few years. Now, scientists are about to get their clearest look yet at chlorophyll fluorescence—and with it, their best accounting of how vegetation worldwide soaks up carbon dioxide—with the launch of NASA’s Orbiting Carbon Observatory-2 (OCO-2) on 1 July. Fluorescence mapping was never part of the original rationale for the $468 million OCO-2, a replacement for a carbonmonitoring satellite that crashed into the ocean 5 years ago. But many on its science team say fluorescence mapping is now the mission’s raison d’être. “In my opinion, this is the most innovative and revolutionary
observation that satellites will make,” says Mike Gunson, the mission’s project scientist at the Jet Propulsion Laboratory (JPL) in Pasadena, California. Other popular proxies for photosynthesis, such as greenness and leaf area, come with problems: An evergreen forest, for example, remains green year-round even though it takes up little carbon in winter. By contrast, a plant fluoresces only when photosynthesis is happening, so the glow directly reflects the amount of carbon that plants take up. Accurate maps of it could correct gaping inaccuracies in global carbon budgets and provide a new tool for assessing how ecosystems will behave under the drought and heat stresses of climate change. The ability to make such maps by satellite is one silver lining in the long wait for an OCO replacement, says JPL’s David Crisp, the science lead for OCO-2 who was principal investigator for OCO. “We didn’t even know we had a measure,” he says. “This is going to tell us where the action is.” Minutes after launch in 2009, a protective clamshell failed to open on the Taurus XL rocket in which OCO rode, and the mission plunked down in the Pacific Ocean. The loss was devastating for climate scientists, who were counting on the satellite to make up for
SCIENCE sciencemag.org
spotty ground measurements of CO2. OCO was designed to monitor a narrow column of air for absorption lines associated with CO2, yielding a global map of its sources and sinks. Some scientists pointed out that the satellite could also help monitor whether countries were complying with emissionsreductions requirements in possible future international climate treaties. Researchers rounded up political support for a replacement. By 2010, JPL had authorization and money to build OCO-2, with as few changes as possible. Then, in 2011, a similar failure of the Taurus XL—built by Orbital Sciences, of Dulles, Virginia—sent another NASA earth science mission, Glory, to a watery grave. NASA had had enough: It decided to move OCO-2 onto a Delta II rocket. That forced another delay on the OCO-2 team— but one that wasn’t entirely unhelpful. In that time, the team learned about problems with a brand of spinning inertial wheels, used for pointing satellites, that crippled the planet-hunting telescope Kepler in 2013. The team had time to swap them out. Meanwhile, chlorophyll fluorescence science came of age. In 2009, the Japanese space agency launched the Greenhouse Gases Observing Satellite (GOSAT). GOSAT can’t map CO2 in as much detail as OCO-2 will, but it has similar spectral resolution: the ability to tease apart reflected sunlight. Working with GOSAT data, several groups realized that to measure CO2 amid the interference from clouds and aerosols, they would have to identify—and subtract—the fluorescence signal anyway. “As we say in our business, one person’s noise is another’s signal,” says Joanna Joiner, a remote sensing scientist at NASA’s Goddard Space Flight 13 JUNE 2014 • VOL 344 ISSUE 6189
Published by AAAS
1211
Downloaded from www.sciencemag.org on June 15, 2014
IN DEP TH
NEWS | I N D E P T H
Center in Greenbelt, Maryland, and one of the pioneers of the technique. The CO2-mapping ability of GOSAT and OCO-2 gets at the net exchange of CO2 above a particular region. With the fluorescence signal, researchers can drill down farther and get the two components that make up the net exchange: carbon uptake through photosynthesis and carbon losses through respiration. And they can watch how these factors evolve with time under different climate conditions. Already, GOSAT data has provided clues: a study published in March in the Proceedings of the National Academy of Sciences found that the U.S. corn belt has a peak fluorescence brighter than anywhere else in the world—and that climate models may be underestimating the region’s carbon uptake by 50% to 75%. Fluorescence measurements could also help resolve a long-standing debate about how the Amazon rainforest responds to droughts—which are expected to occur more often as the world warms. Some scientists have argued that photosynthesis in the Amazon’s dense canopy is limited not by water but by light, so increased sunshine during droughts can lead to a “greening up.” A 2013 paper in the Proceedings of the Royal Society B based on GOSAT data suggests otherwise: During the dry season in some parts of the Amazon, fluorescence—and photosynthesis— went down, even as another proxy for production, the leaf area index, peaked. The applications could extend well beyond climate science. OCO-2’s resolution is about 2 kilometers. With subkilometer spatial resolution, a fluorescence mapper could assess the productivity of different crops in patchwork fields. That could lead to a more accurate picture of global crop yields and how they respond to drought or heat waves—valuable information for adapting to climate change. “Are we planting the right crops in the right place in a changing climate?” asks Matthias Drusch, the European Space Agency (ESA) project scientist for the Fluorescence Explorer (FLEX), a proposed mapper with 300-meter resolution. The €100 million FLEX is one of two finalists competing for an ESA mission selection in 2015. Crisp knows firsthand how hard it can be to see these missions to fruition. He says he has been working 80-hour weeks ever since first proposing OCO to NASA in 2001. Though he feels some trepidation about the upcoming launch, he plans on watching it from the launch site at Vandenberg Air Force Base in California. “We’ve done everything we can,” he says. “God, I hope we get it right. I really want to get it up there. We’ve just got to do this.” ■ 1212
INFECTIOUS DISEASES
Polio eradicators struggle to prevent the next outbreak A new “Red List” identifies the countries where the virus may strike next By Leslie Roberts
T
hey should have seen it coming. Instead, the Global Polio Eradication Initiative (GPEI) was caught flatfooted by the massive outbreak last year in Somalia, Ethiopia, and Kenya, countries where the disease had previously been eliminated. At least that is the opinion of an influential board of outside experts tasked with keeping the eradication effort on track.
The Red List Polio outbreaks waiting to happen
Red List Infected At risk* *Vulnerable, but coordinated response already under way Source: The Global Polio Eradication Initiative
In its characteristic blunt style, the Independent Monitoring Board (IMB) had blasted the eradication program: “The outbreak in the Horn of Africa shows up the program’s surprising disregard for the value of preventing outbreaks,” it wrote in an October 2013 report. “In failing to address a plethora of red flags, it is almost as if the program has operated in the belief that it would ‘remain lucky.’ ” In response, GPEI last month unveiled a carefully honed “Red List”—a global top 10 list of countries at greatest risk of a devastating polio outbreak—which is supposed to help the eradication campaign focus its finite resources. But IMB still isn’t satisfied. In a report released in late May, it pushes GPEI to go further, calling the program’s approach to preventing outbreaks “rudimentary,” “slow,” and “unsophisticated.” And
that’s a major reason, along with killings of polio workers and turmoil in Pakistan, that the goal of stopping all polio transmission in 2014 is at “extreme risk.” “We got hammered,” says Bruce Aylward, who runs GPEI as an assistant directorgeneral at the World Health Organization (WHO) in Geneva, Switzerland. But he admits that the May report is “100% fair.” Under the harsh language lies a very real question: Just how good are the prognostications, and even if they are right, is it re-
RED LIST COUNTRY
PROBABILITY OF IMPORTATION
POTENTIAL SEVERITY
Angola
Medium
High
Benin
Medium
High
CAR
High
High
Chad
High
High
Congo
High
Medium
DR Congo
Medium
High
Gabon
High
High
Ivory Coast
Medium
High
Mali
High
High
Niger
High
High
ally possible to prevent new outbreaks in every polio-free country? Much of GPEI’s effort goes into chasing the polio virus from the only three countries where viral transmission has never stopped: Afghanistan, Pakistan, and Nigeria. But surprise outbreaks of the virus happen every so often in places where the disease was already wiped out and vaccination rates have fallen, costing the program precious time, money, and credibility. In addition to the three countries in the Horn of Africa, five others were hit last year, bringing the total case count to 407, up from 2012’s historic low of 223. For the past few years, WHO, the U.S. Centers for Disease Control and Prevention (CDC), and the Bill & Melinda Gates Foundation, which supports the Seattle, Washington–based modeling group Global Good, sciencemag.org SCIENCE
13 JUNE 2014 • VOL 344 ISSUE 6189
Published by AAAS
Chlorophyll fluorescence from crops can be detected, here by an aerial sensor called HyPlant.
REMOTE SENSING
Carbon-mapping satellite will monitor plants’ faint glow Launch of Orbiting Carbon Observatory-2 promises precise mapping of chlorophyll fluorescence from space
PHOTO: AIRBORNE SENSOR HYPLANT OF THE IBG-2/FORSCHUNGSZENTRUM JÜLICH/GERMANY
By Eric Hand
I
t’s a lesson learned in grade school: Sunlight falls on the leaf, and, catalyzed by chlorophyll, atmospheric carbon dioxide is absorbed and fixed inside a sugar molecule. But there’s also a startling extra credit factoid: The leaf re-emits 1% of that sunlight as a faint red glow. Plant physiologists have known about chlorophyll fluorescence for decades. However, the ability to map this weak signal from space, through the confounding murk of Earth’s atmosphere, has arrived only in the past few years. Now, scientists are about to get their clearest look yet at chlorophyll fluorescence—and with it, their best accounting of how vegetation worldwide soaks up carbon dioxide—with the launch of NASA’s Orbiting Carbon Observatory-2 (OCO-2) on 1 July. Fluorescence mapping was never part of the original rationale for the $468 million OCO-2, a replacement for a carbonmonitoring satellite that crashed into the ocean 5 years ago. But many on its science team say fluorescence mapping is now the mission’s raison d’être. “In my opinion, this is the most innovative and revolutionary
observation that satellites will make,” says Mike Gunson, the mission’s project scientist at the Jet Propulsion Laboratory (JPL) in Pasadena, California. Other popular proxies for photosynthesis, such as greenness and leaf area, come with problems: An evergreen forest, for example, remains green year-round even though it takes up little carbon in winter. By contrast, a plant fluoresces only when photosynthesis is happening, so the glow directly reflects the amount of carbon that plants take up. Accurate maps of it could correct gaping inaccuracies in global carbon budgets and provide a new tool for assessing how ecosystems will behave under the drought and heat stresses of climate change. The ability to make such maps by satellite is one silver lining in the long wait for an OCO replacement, says JPL’s David Crisp, the science lead for OCO-2 who was principal investigator for OCO. “We didn’t even know we had a measure,” he says. “This is going to tell us where the action is.” Minutes after launch in 2009, a protective clamshell failed to open on the Taurus XL rocket in which OCO rode, and the mission plunked down in the Pacific Ocean. The loss was devastating for climate scientists, who were counting on the satellite to make up for
SCIENCE sciencemag.org
spotty ground measurements of CO2. OCO was designed to monitor a narrow column of air for absorption lines associated with CO2, yielding a global map of its sources and sinks. Some scientists pointed out that the satellite could also help monitor whether countries were complying with emissionsreductions requirements in possible future international climate treaties. Researchers rounded up political support for a replacement. By 2010, JPL had authorization and money to build OCO-2, with as few changes as possible. Then, in 2011, a similar failure of the Taurus XL—built by Orbital Sciences, of Dulles, Virginia—sent another NASA earth science mission, Glory, to a watery grave. NASA had had enough: It decided to move OCO-2 onto a Delta II rocket. That forced another delay on the OCO-2 team— but one that wasn’t entirely unhelpful. In that time, the team learned about problems with a brand of spinning inertial wheels, used for pointing satellites, that crippled the planet-hunting telescope Kepler in 2013. The team had time to swap them out. Meanwhile, chlorophyll fluorescence science came of age. In 2009, the Japanese space agency launched the Greenhouse Gases Observing Satellite (GOSAT). GOSAT can’t map CO2 in as much detail as OCO-2 will, but it has similar spectral resolution: the ability to tease apart reflected sunlight. Working with GOSAT data, several groups realized that to measure CO2 amid the interference from clouds and aerosols, they would have to identify—and subtract—the fluorescence signal anyway. “As we say in our business, one person’s noise is another’s signal,” says Joanna Joiner, a remote sensing scientist at NASA’s Goddard Space Flight 13 JUNE 2014 • VOL 344 ISSUE 6189
Published by AAAS
1211
Downloaded from www.sciencemag.org on June 15, 2014
IN DEP TH
NEWS | I N D E P T H
Center in Greenbelt, Maryland, and one of the pioneers of the technique. The CO2-mapping ability of GOSAT and OCO-2 gets at the net exchange of CO2 above a particular region. With the fluorescence signal, researchers can drill down farther and get the two components that make up the net exchange: carbon uptake through photosynthesis and carbon losses through respiration. And they can watch how these factors evolve with time under different climate conditions. Already, GOSAT data has provided clues: a study published in March in the Proceedings of the National Academy of Sciences found that the U.S. corn belt has a peak fluorescence brighter than anywhere else in the world—and that climate models may be underestimating the region’s carbon uptake by 50% to 75%. Fluorescence measurements could also help resolve a long-standing debate about how the Amazon rainforest responds to droughts—which are expected to occur more often as the world warms. Some scientists have argued that photosynthesis in the Amazon’s dense canopy is limited not by water but by light, so increased sunshine during droughts can lead to a “greening up.” A 2013 paper in the Proceedings of the Royal Society B based on GOSAT data suggests otherwise: During the dry season in some parts of the Amazon, fluorescence—and photosynthesis— went down, even as another proxy for production, the leaf area index, peaked. The applications could extend well beyond climate science. OCO-2’s resolution is about 2 kilometers. With subkilometer spatial resolution, a fluorescence mapper could assess the productivity of different crops in patchwork fields. That could lead to a more accurate picture of global crop yields and how they respond to drought or heat waves—valuable information for adapting to climate change. “Are we planting the right crops in the right place in a changing climate?” asks Matthias Drusch, the European Space Agency (ESA) project scientist for the Fluorescence Explorer (FLEX), a proposed mapper with 300-meter resolution. The €100 million FLEX is one of two finalists competing for an ESA mission selection in 2015. Crisp knows firsthand how hard it can be to see these missions to fruition. He says he has been working 80-hour weeks ever since first proposing OCO to NASA in 2001. Though he feels some trepidation about the upcoming launch, he plans on watching it from the launch site at Vandenberg Air Force Base in California. “We’ve done everything we can,” he says. “God, I hope we get it right. I really want to get it up there. We’ve just got to do this.” ■ 1212
INFECTIOUS DISEASES
Polio eradicators struggle to prevent the next outbreak A new “Red List” identifies the countries where the virus may strike next By Leslie Roberts
T
hey should have seen it coming. Instead, the Global Polio Eradication Initiative (GPEI) was caught flatfooted by the massive outbreak last year in Somalia, Ethiopia, and Kenya, countries where the disease had previously been eliminated. At least that is the opinion of an influential board of outside experts tasked with keeping the eradication effort on track.
The Red List Polio outbreaks waiting to happen
Red List Infected At risk* *Vulnerable, but coordinated response already under way Source: The Global Polio Eradication Initiative
In its characteristic blunt style, the Independent Monitoring Board (IMB) had blasted the eradication program: “The outbreak in the Horn of Africa shows up the program’s surprising disregard for the value of preventing outbreaks,” it wrote in an October 2013 report. “In failing to address a plethora of red flags, it is almost as if the program has operated in the belief that it would ‘remain lucky.’ ” In response, GPEI last month unveiled a carefully honed “Red List”—a global top 10 list of countries at greatest risk of a devastating polio outbreak—which is supposed to help the eradication campaign focus its finite resources. But IMB still isn’t satisfied. In a report released in late May, it pushes GPEI to go further, calling the program’s approach to preventing outbreaks “rudimentary,” “slow,” and “unsophisticated.” And
that’s a major reason, along with killings of polio workers and turmoil in Pakistan, that the goal of stopping all polio transmission in 2014 is at “extreme risk.” “We got hammered,” says Bruce Aylward, who runs GPEI as an assistant directorgeneral at the World Health Organization (WHO) in Geneva, Switzerland. But he admits that the May report is “100% fair.” Under the harsh language lies a very real question: Just how good are the prognostications, and even if they are right, is it re-
RED LIST COUNTRY
PROBABILITY OF IMPORTATION
POTENTIAL SEVERITY
Angola
Medium
High
Benin
Medium
High
CAR
High
High
Chad
High
High
Congo
High
Medium
DR Congo
Medium
High
Gabon
High
High
Ivory Coast
Medium
High
Mali
High
High
Niger
High
High
ally possible to prevent new outbreaks in every polio-free country? Much of GPEI’s effort goes into chasing the polio virus from the only three countries where viral transmission has never stopped: Afghanistan, Pakistan, and Nigeria. But surprise outbreaks of the virus happen every so often in places where the disease was already wiped out and vaccination rates have fallen, costing the program precious time, money, and credibility. In addition to the three countries in the Horn of Africa, five others were hit last year, bringing the total case count to 407, up from 2012’s historic low of 223. For the past few years, WHO, the U.S. Centers for Disease Control and Prevention (CDC), and the Bill & Melinda Gates Foundation, which supports the Seattle, Washington–based modeling group Global Good, sciencemag.org SCIENCE
13 JUNE 2014 • VOL 344 ISSUE 6189
Published by AAAS
