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Texas Burns But What's the Global Fire Trend?

Wildfires that have destroyed more than a thousand homes and threaten thousands more continue to rage in central Texas. Meteorologists point out that drought and an influx of wind from Tropical Storm Lee have fanned the flames and fueled the rash of fires, the most severe Texas has experienced in recent memory.

But what do we know about the broader context of the fires? Can we say with any certainty, for example, that fires have become more common in the United States – and across the globe – in the last few decades as global temperatures have increased?

The answer to that question, I found after hunting through various journal articles and checking in with some of Goddard Space Flight Center’s fire specialists, is complex. Satellites offer the most comprehensive and reliable measure of the amount of land burned each year; however, satellite-based records of fire activity are still relatively brief.

The longest fire record I’ve seen published so far, a piece of research authored by Goddard’s Louis Giglio and the University of California, Irvine’s James Randerson, goes back about thirteen years, not long enough to make particularly definitive statements about the nature of long-term fire trends. (The launch of the NPOESS Preparatory Project (NPP) this October will help as it will carry an instrument capable of monitoring fires that should add another five-to-ten years to the long-term record.)

Still, Giglio and his colleagues have pieced together hints of trends that are worth noting. Between 1997 and 2008, they show that the number of hectares burned across the globe has declined a significant amount from a maximum in 1998 to a minimum in 2008 (see graph above). The area burned in the United States, which is less than a percent of the total area burned each year, has seen peaks in 2000 and 2007 (see graph below).

What’s driving the global decline in area burned? The topic is ripe for more research, but when I asked Giglio that question he reminded me that, contrary to what one might expect, increasing global temperatures and drought do not invariably produce increases in fire activity.

The local vegetation and climate makes a big difference, Giglio explained, noting that in certain water-limited areas, such as portions of Australia and Africa (parts of the world where the majority of burning occurs), drought can actually make wildfires less likely to occur by limiting the growth of fuel. The opposite, however, is true in places that receive moderate amounts of rain during the wet season, such as the western United States, a region for which its thought that drought will increases fire activity.

For more on this topic, read Giglio and Randerson’s study in the journal Biogeosciences. For more on how satellite are used to monitor wildfires, visit the University of Maryland’s MODIS fire monitoring page. For coverage of breaking fires, visit NASA’s Smoke and Fire page and the Earth Observatory’s Natural Hazards Fire page. For a NOAA website that highlights fire trend data, visit this page.

Text and graphs by Adam Voiland.Graphics based on satellite-derived burned area data published by Louis Giglio in 2009 (see table 2). Panoramic view of Texas wildfires captured by an astronaut on the International Space Station. Annotation by the Earth Observatory.

Black Carbon's Day on the Hill

Drew Shindell (left), Veerabhadran Ramanathan, and Tami Bond speak with Representative Edward Markey after the three scientists testified. Credit: NASA/Voiland

Leading aerosol scientists, including NASA’s Drew Shindell, explained the intricacies of a sooty component of smoke called black carbon to members of the Select Committee on Energy Independence and Global Warming during a hearing on Capitol Hill last month.

Their message: controlling black carbon emissions could be a win-win for both human health and the environment.

Not only can partially combusted particles of carbon lodge in the human respiratory system and cause disease, the panelists explained, they also contribute to climate change by warming the atmosphere and changing the way Earth reflects sunlight back into space.

Three lawmakers—Representative Edward Markey (D-Mass.), Representative Jay Inslee (D-Wash.), and Representative Emanuel Cleaver (D-Mo.)—questioned the scientists.

Tami Bond, a black carbon specialist from the University of Illinois, began the hearing by offering a summary of black carbon’s potent short-term climate impacts. She noted, for example, that:

• One ounce of black carbon absorbs as much sunlight as would fall on an entire tennis court.

• A pound of black carbon absorbs 650 times as much energy during its one-to-two week lifetime as one pound of carbon dioxide gas would absorb during 100 years.

• An old diesel truck driving 20 miles would emit about one-third of an ounce of black carbon and 70 pounds of carbon dioxide. The carbon dioxide from that truck would have five times the warming power of the black carbon, but it would spread out over 100 years. The truck’s more potent black carbon impact would have an effect in the span of a few weeks.

Drew Shindell, a climate modeler from NASA’s Goddard Institute for Space Studies (GISS) in New York City, provided more details about where black carbon comes from and how much impact it has on Earth’s climate.

As seen in this scanning electron microscope still image, small chain-like aggregates of soot cling to larger sulfate aerosol particles. Credit: Arizona State University/Peter Buseck

Diesel vehicles, agricultural burning and wildfires, and residential cooking stoves are key sources of black carbon. However, combustion that occurs at higher temperatures — such as the type that takes place in power plants — does not produce much of the substance.

Shindell said climate models from NASA GISS and elsewhere show that 15 to 55 percent of global warming is due to black carbon. The wide range is primarily because of incomplete knowledge about how black carbon and clouds interact.

One of the more interesting questions came from Rep. Inslee, who asked the scientists whether black carbon’s impact is due to the fact that it absorbs sunlight and warms the atmosphere, or because it covers snow and ice with dark soot, which reduces Earth’s albedo and makes the planet less reflective.

Veerabhadran Ramanathan , a professor at the Scripps Institution of Oceanography, responded: “The albedo effect contributes about 10 percent of the total black carbon effect. But if you look in the Arctic or in the alpine glaciers, then the darkening effect may be the dominant effect.”

Shindell added that the scientific understanding of black carbon’s impact varies by region. “In places like the Himalayas, the results are somewhat ambiguous,” said Shindell. Over Himalayan glaciers, large amounts of dust — which also absorb radiation — and other pollutants in the air may dampen the effect. “In the Arctic, which tends to be very far from dust sources, the snow is very clean, so the effect is extremely large.” Increasing levels of black carbon combined with decreasing levels of sulfates may account for more than half of the accelerated warming in the last few decades, Shindell’s research suggests.

Inslee also expressed frustration about the lack of understanding of science and climate change among his fellow lawmakers.”If I was scientist and I knew what was going on out there, I’d be in somebody’s grill, telling them we need action,” he said. “And yet you just don’t see that from the scientific community….Why doesn’t that happen? Should it happen?”

Drew Shindell testifies as Veerabhadran Ramanathan looks on.
Credit: Committee on Energy Independence and Global Warming

The scientific method and the culture of scientists, Bond replied, makes it very difficult for scientists to lobby lawmakers or advocate a policy position and remain credible. “This is a difficult question and has to do with the nature of scientists and how they approach science,” she said. “If you have an action outcome, one is almost afraid that you’ll affect the science because you’re supposed to look at it dispassionately. How we conduct our business, 99.9 percent of the time, we must step back from what we want the outcome to be. We’re not allowed to want an outcome.”

— Adam Voiland, NASA’s Earth Science News Team

Tracking Hurricane Irene?

As Hurricane Irene strengthens and threatens the East Coast, it seems a particularly apt time to dust off this 2007 video that explains how hot towers – immensely tall cumulonimbus clouds at the center of tropical cyclones – play a key role in strengthening storms. In 2004, researchers at Goddard Space Flight Center found that a tropical cyclone with a hot tower in its eyewall (the part of a storm the most damaging winds and rain occur) was twice as likely to intensify within the next six hours than a cyclone that lacked a tower. NASA satellites did, as detailed here, observe hot towers in Irene before forecasters elevated the storm to hurricane status.

Tracking Irene? Here are some useful links:

The National Hurricane Center
NASA’s Hurricane Resource Page
The Earth Observatory’s Irene Page
The Tropical Rainfall Measuring Mission (TRMM) Page
@NASAHurricane

Text by Adam Voiland. Image from the Earth Observatory.

Research Roundup: Wandering Storms, Arctic Ozone Loss, and More

Wandering Storms in a Warming World
Most people know climate change is causing glaciers to retreat in Earth’s polar regions, but that’s hardly the only change warming temperatures can produce. A new study, led by Frida Bender of the Scripps Institute of Oceanography and published in Climate Dynamics, shows that the tracks of mid-latitude storms – the type that drives the weather systems that affect Americans the most – have shifted poleward and narrowed over the last 25 years as a result of climate change. What’s more, as the Jet Propulsion Laboratory’s Graeme Stephens notes in a Nature Climate Change article about the study, Bender’s satellite-based research shows that the cloudiness of the storm tracks has decreased over the same period. That’s important as it suggests the decline may have increased the net flux of radiation at the top of Earth’s atmosphere over storms – a process that could amplify warming over time.

Ocean Temperatures a Factor in Arctic Ozone Loss
In March of 2011, the World Meteorological Organization put out a statement announcing an unprecedented loss of stratospheric ozone over the Arctic. Between the beginning of winter and late March ozone levels declined by 40 percent due to unusually cold temperatures in the Arctic stratosphere. (Cold temperatures hasten ozone destruction by making it possible for a certain type of cloud to form that hosts ozone-depleting chemical reactions). But what caused the cold spell? A new study authored by Margaret Hurwitz of Goddard Space Flight Center and published in Atmospheric Chemistry and Physics Discussions points out that unusually warm sea surface temperatures in the North Pacific likely played a key role. The phase of the solar cycle, greenhouse gas emissions, nor El Niño/La Niña oscillations can fully the explain the unusual conditions, she notes.

Can Satellites Help Save the Burrowing Owl?
Burrowing owls, one of the world’s smallest owl species, live in the abandoned tunnels of small mammals such as ground squirrels and prairie dogs. The long-legged birds, which typically weigh just 6 ounces, are losing ground to development and some conservation groups put the number of breeding burrowing owls at a mere 10,000. A new study, published in the Canadian Journal of Remote Sensing, suggests that crop classification imagery from Landsat satellites could be used to evaluate owl demographics and help with conservation plans as agricultural areas experience short-term changes.

Hang Tight, LandSat 5
Speaking of LandSat, Landsat 5, launched in 1984, is still operating more than a quarter of a century later despite having an original design life of three years. However, the reality that LandSat 5’s critical Thematic Mapper instrument, which many agencies around the world rely upon, won’t last indefinitely is becoming increasingly difficult for scientists to ignore as the satellite ages. Since Landscape 6 failed to reach orbit and LandSat 7’s Enhanced Thematic Mapper, which reached orbit in 1999, has a glitch that omits key strips of images, there’s a real possibility that top-tier LandSat images won’t be available until the Landsat Data Continuity Mission launches in December of 2012, a new study in the Canadian Journal or Remote Sensing cautions. The Australian authors of the study tested some of the alternative satellite data products, but none of them quite measured up to LandSat 5 in their view.

Locavores Take Note
Climate models generally assume that the carbon agricultural crops take up later reenters the atmosphere in approximately the same geographic area, but in reality food gets shipped long distances before we consume it. A new paper, authored by Tristram West of the Pacific Northwest National Laboratory (PNNL) and published in Biogeosciences, accounts for the mobile nature of food and shows how regions that rely on food from distant areas end up releasing the carbon that comes with it into the atmosphere. Overall, as noted in the PNNL press release, the researchers found that crops take in — and later return — about 37 percent of the U.S.’s total annual carbon dioxide emissions, but that the amount varies significantly by region. Agriculturally active regions of the Midwest, Great Plains, and along the southern half of the Mississippi (shown in blue below) release more carbon than they take in, while more urban parts of the Northeast, Southeast, Western U.S. and Gulf Coast (shown in red below) take in more than they release.

Text by Adam Voiland. Extratropical storm imagery from the Earth Observatory. Burrowing owl imagery from the city of Boulder. Agricultural carbon sink and source map from Science Daily.

What on Earth is That #9

What on Earth is That?

Here at What on Earth we’re offering an extra special “no prize” if you can correctly identify the large blob-like objects and the smaller objects pointed at by the arrows. Post your guesses in the comments section, and check back next week for the answer.

Here’s the question from last time

And a time before that
And that
And…

Ice Conditions — Not Just Japanese Tsunami — Key to Antarctic Iceberg Break Off

Today’s big Earth science news was that the earthquake and tsunami that struck Japan in March was strong enough to send waves that snapped a Manhattan-sized chunk of ice off the Sulzberger Ice Shelf some 8,100 miles away.

That’s true, but as pointed out at the end of this piece there’s more to this story than just the strength of the earthquake. Though it’s not making it into the headlines, the condition of the ice in the region was also key. Specifically, the lack of nearby sea ice, coastal ice (also called fast or landfast ice) and pack ice made the portion of the Sulzberger Ice Shelf that broke off particularly susceptible to the incoming waves from the tsunami. Here’s how Kelly Brunt, the Goddard scientist who made the discovery, explained it in her Journal of Glaciology paper [pdf]. The bolding is mine.

The recent calving from the Sulzberger Ice Shelf suggests that, while the rifts provide the ice-shelf front with a zone that is weakened with respect to stress, and while tsunamis arrive episodically to cause vibrational disturbances to these rifts, some additional enabling condition must be satisfied before a given tsunami can lead to the detachment of an iceberg.

The timing of the earthquake and tsunami in Japan coincided with the typical summer sea-ice minimum (Zwally and others, 2002). As observed in the MODIS imagery and confirmed in the ASAR imagery, the region north of the Sulzberger Ice Shelf was devoid of either fast or pack ice at the time of predicted arrival of the tsunami. Fast ice is an important factor in ice shelf stability (Massom and others, 2010). Additionally, the absence of sea ice meant that the energy associated with the tsunami incident on the ice-shelf front was not damped by sea-ice flexure. With a distant tsunami source, over an irregular ocean bathymetry, and taking into account the dispersion of high-frequency components of the tsunami outside the shallow-water approximation, a complex pattern of dispersed waves is predicted in the wake of the leading front of the tsunami (NOAA/PMEL/Center for Tsunami Research; http://nctr.pmel.noaa.gov). As these waves interacted with the ice shelf over a period of hours to days, flexural modes may have been resonantly excited, each with the potential to trigger iceberg calving (Holdsworth and Glynn, 1978), in a pattern reminiscent of the delayed response of harbors documented in the far field during the 2004 Sumatra tsunami (Okal and others, 2006).

This study presents the first observational evidence linking a tsunami to ice-shelf calving. Specifically, the impact of the tsunami and its train of following dispersed waves on the Sulzberger Ice Shelf, in combination with the ice-shelf and sea ice conditions, provided the fracture mechanism needed to trigger the first calving event from the ice shelf in 46 years

Text by Adam Voiland. Imagery from the European Space Agency/Envisat.

Humisery 2011: No Ordinary View of Air Pollution

A video camera on board NASA’s P-3B aircraft captured this vertigo-inducing view of Baltimore’s suburbs as part of an air pollution-monitoring mission called Discover-AQ. The P3-B, loaded with multiple pollution sensors, has been cruising along major transportation corridors in the Washington-Baltimore metro area and flying spirals over six ground stations throughout July. Meanwhile, a smaller aircraft, a UC-12, has been flying along the same approximate flight path but at higher altitude of about 26,000 feet. View the animation below to see the flight paths of both planes.

The goal of the flights is to help piece together a more accurate view of the vertical distribution of air pollution by looking simultaneously at the same pollution events with ground, aircraft, and satellite instruments. Flights for this summer will wrap up by July 29th.

The researchers involved in the project haven’t had time to rigorously analyze the data their instruments have collected and publish findings in peer-reviewed science journals yet, but many have posted raw results from the various instruments on Discover-AQ’s science website.

I paged through many of the daily reports and found quite a number of intriguing nuggets of information. For now, though, I’ll share just one set of images – a comparison of particulate pollution levels on July 1 with levels on July 22nd. The data comes from the High Spectral Resolution Lidar (HSRL), a sensor on the UC-12 that uses a radar-like laser technology called lidar to map the distribution of small particles of pollution. HSRL generates data “slices” that show the vertical distribution of the particles, known generally as aerosols, from ground level up to eight kilometers.

July 1 Flight (minimal particulate air pollution)

July 22nd Flight (heavy particulate air pollution)

In the HSRL data readouts, high levels of aerosols are shown in red and yellow, while lower levels of particles are shown in blue. On the first day of science flights – July 1st – temperatures were moderate and aerosol levels were low. By the tenth flight, the mid-Atlantic was in the midst of a brutal heat wave (which the Star-Ledger weather team want to call Humisery11), and both ozone and particulate counts from ground stations had shot up.

The HSRL slices capture the difference between clear and pollution-laden skies beautifully. The first flight shows just moderate levels of ground-level pollution – the yellow band in the image below that reaches up to about 3 kilometers. In contrast, the flight on the 22nd, a day that temperatures in Baltimore hit 105 °F, shows a deep red swath of particle pollution near the surface.

HSRL data can be a little confusing to make sense of when you first see it, so realize that scientists plot the data out in a horizontal strip with the passage of time on the upper x axis (the numbers with the UT units) and the latitude and longitude on the lower x axis. Altitude is shown on the y-axis. The two images below should help you see how the strips of data relate to the trapezoidal flight paths.

July 1st Flight

July 22nd Flight

Text by Adam Voiland. Flight video from P3-B camera. Flight path visualization from the SVS. Data charts from the July 1st and July 22nd HSRL flight reports.

Listen to the Sound of a Ship's Hull Gouging Through First-Year Ice

What on Earth was that grinding, thudding, scraping sound? No, it wasn’t astronauts clumping around on the Space Station, a washing machine in the midst of a cycle, or space dust hammering the Space Shuttle. It was actually the Coast Guard’s newest and most technologically advanced ice breaker — the Healy — barreling through thin, first-year ice in the Chukchi Sea north of Alaska. (Multiyear ice tends to be less briny and have more air bubbles than first-year ice.) NASA science writer Kathryn Hansen is on board as part of the ICESCAPE mission, and she had this to say about the sound:

On July 7, I took a trip down into the bowels of the Healy’s bow to record the sound of the ship’s hull pummeling through thin, first-year ice (mp3 above). The rhythm and crescendos reminded me of the percussion section of an amateur orchestra.

Interestingly, icebreaking sounds completely different depending on your location in the ship. From outside on the ship’s deck you can hear the ice cracking and ocean water rushing in to fill the void. From inside in the science lounge, add the effect of vibrating bookshelves and the demise of items not properly secured.

These sounds (not to mention the earthquake-like movement) eventually blend into the background and sleep comes easily. The strange part will be returning home at the end of the month to a “quiet and still” life in the city.

By now you might be wondering, how much ice can the Healy break? Cruising at 3 knots, the ship is rated to break 4.5 feet of ice. By backing and ramming, the ship can break through 8 feet. Breaking thicker ice is possible but would take more time.

Hansen has also filed a few web videos about the expedition featuring interviews with ICESCAPE Project Scientist Kevin Arrigo and Karen Frey of Clark University that are worth checking out.

Researchers Release Longest Single-Satellite Aerosol Record to Date

With the help of measurements from a now defunct satellite called SeaWifs, researchers from NASA’s Goddard Space Flight Center, led by Christina Hsu, have developed the longest single-satellite global record of aerosols to date. (Not sure what an aerosol is or what it has to do with the climate? Read this.)

The SeaWiFS aerosol record runs between 1997 and 2010 and will complement existing records from the MISR and MODIS instruments. Since these two important records don’t agree particularly well over land, scientists hope that data from other outside sensors like SeaWiFS might help resolve some of the discrepancies and reduce the overall uncertainty in the aerosol portion of climate models.

The SeaWiFS record isn’t the only new tool coming online for aerosol climatologists. In October, a new satellite, the NPOESS Preparatory Project (NPP) will deliver a scanning radiometer called VIIRS into space that will also measure the ubiquitous particles. (Another mission launched in March, Glory, would have helped measure aerosols, but it never reached orbit because of a catastrophic problem with its rocket.)

Patching the VIIRS data together with the older datasets won’t necessarily be easy, but building long-running datasets that span decades — the purpose of many of the satellites that are part of NASA’s Earth Observing System — is the key to getting climate change science right.

Top image of aerosol types (volcanic ash, pollen, sea salt, and soot) was published originally by the Earth Observatory. SeaWiFS’s 13-years aerosol record for Washington DC was originally published here. Peaks show times when aerosols are more abundant. The annual cycle is due to air stagnation in the summer. Text by Adam Voiland.

Research Roundup: Plane-Punched Clouds, the Sahel and More

Plane-Punched Clouds
Here’s a bit of news that ufologists may not like to hear. A new study offers more evidence that airplanes produce the saucer-shaped cloud formations that atmospheric scientists call “hole-punch clouds.” The researchers — including Langley-based Patrick Minnis — found that planes seed the unusual clouds by supercooling air in the wake of propellers and wing tips. The chilled air generates tiny ice droplets that can lead to snow or rainfall. If the precipitation falls quickly enough and the cloud is thin, hole-punch clouds can form. Cloud-punching planes don’t produce enough extra precipitation to impact the global climate, the lead author of the study said, but the effect is widespread. The same process, the Earth Observatory pointed out in 2009, can create narrow “canal clouds” as well.

The Slippery Sahel
The Sahel, an area of semi-arid grassland around the southern limit of the Sahara Desert, is thought to be one of the areas most vulnerable to climate change. Most people in the region rely on rain-fed agriculture, and devastating famines that killed as many as 100,000 people struck the area in the 1970s. But how well can climatologists predict how Sahel precipitation patterns will change over the next 100 years? As part of a new review paper, GISS scientist Leonard Druyan surveyed the literature and found projections are all over the map. Here’s how he explained it: “A variety of model deficiencies, regarding the simulation of one or more of these physical processes, taints models’ climate change projections. Consequently, no consensus emerges regarding the impact of anticipated greenhouse gas forcing on the hydrology of the Sahel in the second half of the 21st century.”

Soil Matters
Soil moisture. Sounds boring, I know. But did you know that patches of dry soil, in certain situations, can actually spark precipitation in ways thatmoist areas don’t? That’s the takeaway of a Nature Geoscience piece penned by Goddard’s Randal Koster that offers a perspective on researchthat suggests storms paradoxically form more easily over areas thathave sharp gradients between moist and dry soil. More work needs to bedone to confirm the finding, but in the meantime here’s to hoping thismeans the less I water my tomatoes the more it will rain.

Get Ready for GPM
You might think the work starts for scientists after a satellite reaches orbits and starts beaming data back to Earth. In fact, studies on the ground and in the lab actually start years – in some cases decades – in advance of a satellite getting anywhere near a rocket. Take, for example, NASA’s Global Precipitation Mission (GPM). Two studies appeared recently that, while not exactly Earth-shattering, lay the scientific groundwork for juicer findings that will come when the core GPM spacecraft launches in July of 2013. One involves a suite of modeling tests that will help researchers do a better job of integrating satellite rainfall data into models. The other proposes a new mathematical approach that will make measurements of rainfall made by microwave instruments over land more accurate.

Polar Bears, Martha Stewart, and Me
You just can’t go wrong with a title to a talk like that. The clip below is from an hour-long talk that Gavin Schmidt gave to colleagues at GISS about his visit to Churchill, a tiny town in Canada that’s known as the polar bear capitol of the world. Yes, Martha Stewart came along as well. The talk doesn’t start until about 1:48, and Schmidt’s interview with Stewart starts at 48:18.

Text by Adam Voiland. Hole-punch cloud photo was published originally on Earth Science Picture of the Day. The photographer is Herbert Raab.