- New maps of burn areas from two California megafires are so detailed, they can show individual trees.
- The maps are being used in rehabilitating the burn areas and protecting wildlife.
Those who feel as though they’ve been living in the never-ending winter of the movie “Frozen” this year may be glad to hear that the spring thaw is now typically arriving up to two weeks earlier in the Northern Hemisphere than it did 20 to 30 years ago. But the changing date of the spring thaw has consequences far beyond reducing the number of mornings when you have to scrape off your windshield.
One ecosystem where scientists would most like to understand the effects of changing freeze/thaw cycles is boreal forests, the great ring of green covering the land nearest the North Pole. The forests of Alaska, Canada, Scandinavia and Siberia cover almost 15 percent of Earth’s land surface. The Arctic is warming more quickly than lower latitudes, and the way these forests respond to this rapid change could provide valuable clues about our planet’s warmer future.
But we know very little about how the boreal forests are changing. Millions of square miles have no roads or even villages. “What we have now are very sparse, seasonal measurements from the ground,” said John Kimball, a professor of systems ecology at the University of Montana, Missoula, and a member of the science team for NASA’s Soil Moisture Active Passive (SMAP) mission, launched Jan. 31. “We do have long-term, global satellite data sets that are sensitive to freeze-thaw, but they tend to be very coarse.” That means each measurement averages the status of a large area. Like a mosaic made of large tiles, these data cannot show much detail.
That’s about to change. By the end of April, SMAP will begin monitoring the frozen or thawed state of the landscape north of 45 degrees north latitude (about the latitude of Minneapolis) every two days. The primary mission of SMAP is to measure the amount of moisture in the top few inches of soil globally, but it also detects whether that moisture is frozen or in liquid form. SMAP’s radar measurements, with “tiles” only half a mile to a mile and a half (1 to 3 kilometers) across, will reveal far more detail than scientists now have about the freeze/thaw status of the land surface.
Why is greater detail needed? In the Arctic, the timing of the spring thaw can vary considerably within a small area. Because the returning sun is low on the horizon, the shadowed north side of a hill may remain icy many days after plants have started growing again on the sunlit south side. Those early spring weeks are critical in the short Arctic growing season. “Once the vegetation thaws, boom! Photosynthesis takes off,” Kimball explained. “You can get your highest rates of photosynthesis within a few weeks after the thaw, and a later thaw can mean much lower vegetation growth for the season. We need observations at what I call the landscape level to more precisely monitor those patterns and changes.”
During photosynthesis, plants absorb carbon dioxide from the air. The carbon stays in their wood, roots and leaves, and when they die, most of it remains in the soil. That makes undisturbed forests what scientists call carbon sinks — places that remove carbon from the atmosphere. Longer unfrozen seasons in the Arctic give forests more time to grow and spread, increasing the extent of the carbon sink.
On the other hand, climate warming has increased the occurrence of droughts and wildfires in the Arctic. A burning forest spews enormous amounts of carbon into the atmosphere; in scientific terms, it is a carbon source. Thus, global climate change is causing the northern forests both to absorb and to release more carbon.
With so little Arctic data to crunch, models of Arctic land processes do not agree on which of these trends is prevailing, much less what the future could hold. Lack of consensus does not indicate fundamental disagreements on the physical processes involved, according to JPL scientist Josh Fisher, a member of the SMAP algorithm team. The problem is that, at present, if you put the Arctic’s emitted carbon on one side of a scale and absorbed carbon on the other, the scales would almost balance. “The source/sink balance is usually close to zero, and it’s very easy to get on the wrong side of the zero,” he said. Yet the wrong answer on this fundamental question can cascade into a chain of wrong answers in the course of a model simulation. SMAP’s fine-scale observations have the potential to improve modelers’ understanding of both today’s situation and how it may change in the future.
This spring, SMAP will spin up in time to track the spring thaw in the boreal forest with the detail scientists need — as Princess Anna in “Frozen” says, “For the first time in forever.”
For more about SMAP, visit:
JPL is managed for NASA by the California Institute of Technology in Pasadena.
Researchers at the University of Texas at Austin, NASA and other research organizations have discovered two seafloor troughs that could allow warm ocean water to reach the base of Totten Glacier, East Antarctica’s largest and most rapidly thinning glacier. The discovery likely explains the glacier’s extreme thinning and raises concern about its impact on sea level rise.
The result, published in the journal Nature Geoscience today, March 16, has global implications because the ice flowing through Totten Glacier alone is equivalent to the entire volume of the more widely studied West Antarctic Ice Sheet. If Totten Glacier were to collapse completely, global sea levels would rise by at least 11 feet (3.3 meters). As in the West Antarctic Ice Sheet, complete collapse of Totten Glacier may take centuries, although the timing of retreat in both places is the subject of intensive research.
East Antarctica has appeared to be stable compared with the rapidly melting western side of the continent. The new finding shows that “Totten Glacier and the East Antarctic Ice Sheet are a much more interesting and dynamic part of the sea level rise story than we’d previously thought,” said co-author Dustin Schroeder, a scientist at NASA’s Jet Propulsion Laboratory, Pasadena, California. Schroeder helped analyze data from an ice-penetrating radar to demonstrate that ocean water could access the glacier through the newfound troughs.
In some areas of the ocean surrounding Antarctica, warm water can be found below cooler water because it is saltier, and therefore heavier, than the shallower water. Seafloor valleys that connect this deep warm water to the coast can especially compromise glaciers, but this process had previously been seen only under the West Antarctic Ice Sheet. Deep warm water had been observed seaward of Totten Glacier, but there was no evidence that it could compromise coastal ice.
The newly discovered troughs are deep enough to give the deep warm water access to the huge cavity under the glacier. The deeper of the two troughs extends from the ocean to the underside of Totten Glacier in an area not previously known to be floating.
The data for this study were gathered as part of the International Collaboration for Exploration of the
Cryosphere through Airborne Profiling (ICECAP) project, which, together with the East Antarctic component of NASA’s Operation IceBridge mission, made the first comprehensive survey of the Totten Glacier Ice Shelf and nearby regions between 2008 and 2012. Other coauthors of the study come from research organizations and universities in Australia, France and England.
For more information on the new study, see:
To learn more about Operation IceBridge and ICECAP, visit:
The paper is available at:
It’s active. It’s passive. And it’s got a big, spinning lasso.
Scheduled for launch on Jan. 29, 2015, NASA’s Soil Moisture Active Passive (SMAP) instrument will measure the moisture lodged in Earth’s soils with an unprecedented accuracy and resolution. The instrument’s three main parts are a radar, a radiometer and the largest rotating mesh antenna ever deployed in space.
Remote sensing instruments are called “active” when they emit their own signals and “passive” when they record signals that already exist. The mission’s science instrument ropes together a sensor of each type to corral the highest-resolution, most accurate measurements ever made of soil moisture — a tiny fraction of Earth’s water that has a disproportionately large effect on weather and agriculture.
To enable the mission to meet its accuracy needs while covering the globe every three days or less, SMAP engineers at NASA’s Jet Propulsion Laboratory in Pasadena, California, designed and built the largest rotating antenna that could be stowed into a space of only one foot by four feet (30 by 120 centimeters) for launch. The dish is 19.7 feet (6 meters) in diameter.
“We call it the spinning lasso,” said Wendy Edelstein of NASA’s Jet Propulsion Laboratory, Pasadena, California, the SMAP instrument manager.
Like the cowboy’s lariat, the antenna is attached on one side to an arm with a crook in its elbow. It spins around the arm at about 14 revolutions per minute (one complete rotation every four seconds). The antenna dish was provided by Northrop Grumman Astro Aerospace in Carpinteria, California. The motor that spins the antenna was provided by the Boeing Company in El Segundo, California.
“The antenna caused us a lot of angst, no doubt about it,” Edelstein noted. Although the antenna must fit during launch into a space not much bigger than a tall kitchen trash can, it must unfold so precisely that the surface shape of the mesh is accurate within about an eighth of an inch (a few millimeters).
The mesh dish is edged with a ring of lightweight graphite supports that stretch apart like a baby gate when a single cable is pulled, drawing the mesh outward. “Making sure we don’t have snags, that the mesh doesn’t hang up on the supports and tear when it’s deploying — all of that requires very careful engineering,” Edelstein said. “We test, and we test, and we test some more. We have a very stable and robust system now.”
SMAP’s radar, developed and built at JPL, uses the antenna to transmit microwaves toward Earth and receive the signals that bounce back, called backscatter. The microwaves penetrate a few inches or more into the soil before they rebound. Changes in the electrical properties of the returning microwaves indicate changes in soil moisture, and also tell whether or not the soil is frozen. Using a complex technique called synthetic aperture radar processing, the radar can produce ultra-sharp images with a resolution of about half a mile to a mile and a half (one to three kilometers).
SMAP’s radiometer detects differences in Earth’s natural emissions of microwaves that are caused by water in soil. To address a problem that has seriously hampered earlier missions using this kind of instrument to study soil moisture, the radiometer designers at NASA’s Goddard Space Flight Center, Greenbelt, Maryland, developed and built one of the most sophisticated signal-processing systems ever created for such a scientific instrument.
The problem is radio frequency interference. The microwave wavelengths that SMAP uses are officially reserved for scientific use, but signals at nearby wavelengths that are used for air traffic control, cell phones and other purposes spill over into SMAP’s wavelengths unpredictably. Conventional signal processing averages data over a long time period, which means that even a short burst of interference skews the record for that whole period. The Goddard engineers devised a new way to delete only the small segments of actual interference, leaving much more of the observations untouched.
Combining the radar and radiometer signals allows scientists to take advantage of the strengths of both technologies while working around their weaknesses. “The radiometer provides more accurate soil moisture but a coarse resolution of about 40 kilometers [25 miles] across,” said JPL’s Eni Njoku, a research scientist with SMAP. “With the radar, you can create very high resolution, but it’s less accurate. To get both an accurate and a high-resolution measurement, we process the two signals together.”
SMAP will be the fifth NASA Earth science mission launched within the last 12 months.
For more about the SMAP mission, visit:
NASA monitors Earth’s vital signs from space, air and land with a fleet of satellites and ambitious airborne and ground-based observation campaigns. NASA develops new ways to observe and study Earth’s interconnected natural systems with long-term data records and computer analysis tools to better see how our planet is changing. The agency shares this unique knowledge with the global community and works with institutions in the United States and around the world that contribute to understanding and protecting our home planet.
For more information about NASA’s Earth science activities this year, visit:
Jet Propulsion Laboratory, Pasadena, California
Written by Carol Rasmussen
NASA Earth Science News Team
PRESS RELEASE (NASA/JPL) – A new NASA-led study shows that tropical forests may be absorbing far more carbon dioxide than many scientists thought, in response to rising atmospheric levels of the greenhouse gas. The study estimates that tropical forests absorb 1.4 billion metric tons of carbon dioxide out of a total global absorption of 2.5 billion — more than is absorbed by forests in Canada, Siberia and other northern regions, called boreal forests.
“This is good news, because uptake in boreal forests is already slowing, while tropical forests may continue to take up carbon for many years,” said David Schimel of NASA’s Jet Propulsion Laboratory, Pasadena, California. Schimel is lead author of a paper on the new research, appearing online today in the Proceedings of National Academy of Sciences.
Forests and other land vegetation currently remove up to 30 percent of human carbon dioxide emissions from the atmosphere during photosynthesis. If the rate of absorption were to slow down, the rate of global warming would speed up in return.
The new study is the first to devise a way to make apples-to-apples comparisons of carbon dioxide estimates from many sources at different scales: computer models of ecosystem processes, atmospheric models run backward in time to deduce the sources of today’s concentrations (called inverse models), satellite images, data from experimental forest plots and more. The researchers reconciled all types of analyses and assessed the accuracy of the results based on how well they reproduced independent, ground-based measurements. They obtained their new estimate of the tropical carbon absorption from the models they determined to be the most trusted and verified.
“Until our analysis, no one had successfully completed a global reconciliation of information about carbon dioxide effects from the atmospheric, forestry and modeling communities,” said co-author Joshua Fisher of JPL. “It is incredible that all these different types of independent data sources start to converge on an answer.”
The question of which type of forest is the bigger carbon absorber “is not just an accounting curiosity,” said co-author Britton Stephens of the National Center for Atmospheric Research, Boulder, Colorado. “It has big implications for our understanding of whether global terrestrial ecosystems might continue to offset our carbon dioxide emissions or might begin to exacerbate climate change.”
As human-caused emissions add more carbon dioxide to the atmosphere, forests worldwide are using it to grow faster, reducing the amount that stays airborne. This effect is called carbon fertilization. “All else being equal, the effect is stronger at higher temperatures, meaning it will be higher in the tropics than in the boreal forests,” Schimel said.
But climate change also decreases water availability in some regions and makes Earth warmer, leading to more frequent and larger wildfires. In the tropics, humans compound the problem by burning wood during deforestation. Fires don’t just stop carbon absorption by killing trees, they also spew huge amounts of carbon into the atmosphere as the wood burns.
For about 25 years, most computer climate models have been showing that mid-latitude forests in the Northern Hemisphere absorb more carbon than tropical forests. That result was initially based on the then-current understanding of global air flows and limited data suggesting that deforestation was causing tropical forests to release more carbon dioxide than they were absorbing.
In the mid-2000s, Stephens used measurements of carbon dioxide made from aircraft to show that many climate models were not correctly representing flows of carbon above ground level. Models that matched the aircraft measurements better showed more carbon absorption in the tropical forests. However, there were still not enough global data sets to validate the idea of a large tropical-forest absorption. Schimel said that their new study took advantage of a great deal of work other scientists have done since Stephens’ paper to pull together national and regional data of various kinds into robust, global data sets.
Schimel noted that their paper reconciles results at every scale from the pores of a single leaf, where photosynthesis takes place, to the whole Earth, as air moves carbon dioxide around the globe. “What we’ve had up till this paper was a theory of carbon dioxide fertilization based on phenomena at the microscopic scale and observations at the global scale that appeared to contradict those phenomena. Here, at least, is a hypothesis that provides a consistent explanation that includes both how we know photosynthesis works and what’s happening at the planetary scale.”
NASA monitors Earth’s vital signs from land, air and space with a fleet of satellites and ambitious airborne and ground-based observation campaigns. NASA develops new ways to observe and study Earth’s interconnected natural systems with long-term data records and computer analysis tools to better see how our planet is changing. The agency shares this unique knowledge with the global community and works with institutions in the United States and around the world that contribute to understanding and protecting our home planet.
For more information about NASA’s Earth science activities in the last year, visit:
Jet Propulsion Laboratory, Pasadena, California
Written by Carol Rasmussen
NASA Earth Science News Team