Image Credit: NASA Earth Observatory/Aqua/MODIS/Jeff Schmaltz
In August and September 2015, a massive dust storm swirled across the Middle East. After reporting on the storm, I read a fair amount of speculation — but no clear answers — as to what kicked up such an unusually large amount of dust. Several reports made the case that the ongoing war in Syria was a contributing factor. The war, some scientists speculated, had increased the military traffic over unpaved roads and had led farmers to abandon their land.
Now a new study led by a researcher from Duke University argues that the war was not an important cause. By analyzing satellite data of vegetation cover before the war, the researchers concluded that the conflict did not have much effect on vegetation. (Vegetation helps hold sand and soil in place.) In fact, the satellites observed that agricultural activity was healthy in 2015 in comparison to earlier years.
Rather, the research team found that the key drivers of the dust storm were meteorological. The summer of 2015 was unusually hot and dry compared to the past 20 years, meaning more dust was available and in a condition that winds could easily lift. So when an unusual cyclonic wind pattern developed in late August and persisted for more than a week, a mega dust storm was born.
Read a press release about the study from Princeton University, and read the full study in Environmental Research Letters. To reach their conclusion, the researchers used Aerosol Optical Depth and Normalized Difference Vegetation Index (NDVI) observations from NASA’s Moderate Resolution Imaging Spectroadiomters (MODIS), and meteorological simulations from the Weather Research and Forecasting (WRF) model. You can view several types of satellite imagery of the storm, which began on August 31 and peaked on September 8, on NASA’s Worldview browser.
Global atmospheric concentrations of methane are rising—along with scientific scrutiny of this potent greenhouse gas. In March 2016, we published a feature story that took a broad look at why methane matters. Since that story came out, several new studies have been published. But first, some broader context from that feature story…
The long-term, global trend for atmospheric methane is clear. The concentration of the gas was relatively stable for hundreds of thousands of years, but then started to increase rapidly around 1750. The reason is simple: increasing human populations since the Industrial Revolution have meant more agriculture, more waste, and more fossil fuel production. Over the same period, emissions from natural sources have stayed about the same.
The Zeppelin Observatory in Svalbard monitors methane concentrations. It is one of several stations that helps scientists assemble a global picture of atmospheric aerosols and pollutants. Photo courtesy of AGAGE.
If you focus on just the past five decades—when modern scientific tools have been available to detect atmospheric methane—there have been fluctuations in methane levels that are harder to explain. Since 2005, methane has been on the rise, and no one is quite sure why. Some scientists think tropical wetlands have gotten a bit wetter and are releasing more gas. Others point to the natural gas fracking boom in North America and its sometimes leaky infrastructure. Others wonder if changes in agriculture may be playing a role.
A combination of historical ice core data and air monitoring instruments reveals a consistent trend: global atmospheric methane concentrations have risen sharply in the past 2000 years. (NASA Earth Observatory image by Joshua Stevens, using data from the EPA.)
The stakes are high when it comes to sorting out what is going on with methane. Global temperatures in 2014 and 2015 were warmer than at any other time in the modern temperature record, which dates back to 1880. The most recent decade was the warmest on the record. The current year, 2016, is already on track to be the warmest. And carbon emissions — including methane — are central to that rise.
Atmospheric methane has continued to increase, though the rate of the increase has varied considerably over time and puzzled experts. (NASA Earth Observatory image by Joshua Stevens, using data from NOAA.)
Isotope Data Suggests Fossil Fuels Not to Blame for Increase
Methane bubbles up from swamps and rivers, belches from volcanoes, rises from wildfires, and seeps from the guts of cows and termites (where is it made by microbes). Human settlements are awash with the gas. Methane leaks silently from natural gas and oil wells and pipelines, as well as coal mines. It stews in landfills, sewage treatment plants, and rice paddies. With so many different sources, many scientists who study methane are hesitant to pin the rising concentration of the gas on a particular source until more data is collected and analyzed.
However, an April 2016 study led by a researcher from New Zealand’s National Institute of Water and Atmospheric Research came down squarely on one side. After measuring the isotopic composition, or chemical structure, of carbon trapped in ice cores and archived air samples from a global network of monitoring stations, the scientists concluded that blaming the rise in atmospheric methane on fossil fuel production makes little sense.
When methane has extra neutrons in its chemical structure, it is said to be a “heavier” isotope; fewer neutrons make for “lighter” methane. Different processes produce different proportions of heavy and light methane. Lighter isotopes of a carbon (meaning they have a lower ratio of Carbon 13 to Carbon 12 than the atmosphere), for instance, are usually associated with methane recovered from fossil fuels.
As shown in the chart above, the authors observed a decrease in the isotopes associated with fossil fuels at all latitudes beginning in 2006. But at the same time, global concentrations of methane (blue line in the top chart) have risen. “The finding is unexpected, given the recent boom in unconventional gas production and reported resurgence in coal mining and the Asian economy. Either food production or climate-sensitive natural emissions are the most probable causes of the current methane increase,” the authors noted.
If fossil fuel production is not responsible for increasing concentrations of atmospheric methane, than what is? The authors say that more research is needed to be certain, but that there are indications that the agricultural sector in southeast Asia (especially rice cultivation and livestock production) is likely responsible.
Large Increase in U.S. Emissions over Past Decade
A March 2016 study led by Harvard researchers based on surface measurements and satellite observations detected a 30 percent increase in methane emissions from the United States between 2002 and 2014 — an amount the authors argue could account for between 30 to 60 percent of the global growth in atmospheric methane during the past decade.
The most significant increase (in red, as observed with Japan’s Greenhouse Gases Observing Satellite) occurred in the central United States. However, the authors avoid making claims about why. “The U.S. has seen a 20 percent increase in oil and gas production and a nine-fold increase in shale gas production from 2002 to 2014, but the spatial pattern of the methane increase seen by GOSAT does not clearly point to these sources. More work is needed to attribute the observed increase to specific sources.”
First Time Satellite View of Methane Leaking from a Single Facility
For the first time, an instrument on a spacecraft has measured the methane emissions leaking from a single facility on Earth’s surface. The observation, detailed in a June 2016 study, was made by the hyperspectral spectrometer Hyperion on NASA’s Earth Observing-1 (EO-1) satellite. On three separate overpasses, Hyperion detected methane leaking from the Aliso Canyon gas leak, the largest methane leak in U.S. history.
“The percentage of atmospheric methane produced through human activities remains poorly understood. Future satellite instruments with much greater sensitivity can help resolve this question by surveying the biggest sources around the world and helping us to better understand and address this unknown factor in greenhouse gas emissions,” David Thompson, an atmospheric chemist at NASA’s Jet Propulsion Laboratory and an author of the study. For instance, the upcoming Environmental Mapping and Analysis Program (EnMAP) is a satellite mission (managed by the German Aerospace Center) that will provide new hyperspectral data for scientists for monitoring methane.
As detailed in a July 2016 study, scientists and engineering are also working on a project called GEO-CAPE that will result in the deployment of a new generation of methane-monitoring instruments on geostationary satellites that can monitor methane sources in North and South America on a more continuous basis. Current methane sensors operate in low-Earth orbit, and thus take several days or even weeks before they can observe the same methane hot spot. For instance, EO-1 detected the Aliso Canyon plume just three times between December 29, 2015 and February 14, 2016, due to challenges posed by cloud cover and the lighting angle. A geostationary satellite would have detected it on a much more regular basis.
What is the hottest volcano of them all? It depends on how you define “hottest,” but a fascinating new analysis crunches the numbers in a few different ways, using satellite observations of 95 of Earth’s most active volcanoes since 2000.
In terms of total energy radiated, the prize goes to Hawaii’s Kilauea (shown above), which has been spilling lava continuously throughout the study period. Thanks to its lava lake, Nyiragongo (Democratic Republic of Congo) came in a close second. Africa’s most active volcano — and Nyiragongo’s neighbor — Nyamuragira came in third for overall energy radiated. For a full ranking of all 95 volcanoes, see the chart at the bottom of the bottom of this page.
Note that the volcanoes emitting the most heat do not necessarily emit it explosively. In fact, most of the top heat producers were shield volcanoes that released mafic lava slowly.
If you ignore the steady, continuous heat produced by volcanoes and look simply at the “extra” heat produced during eruptions, then the rankings look different. Iceland’s ongoing Holuhraun eruption has radiated the most heat for an event. At the time that the study was published, Holuhraun had radiated about one-third more thermal energy than the 2012-2013 eruption of Russia’s Tolbachik, which itself radiated about 50 percent more energy than the 2011-2012 eruption of Nyamuragira.
The study, led by Robert Wright of the Hawaii Institute of Geophysics and Planetology, was based on data acquired by the Moderate Resolution Imaging Spectroradiometers on NASA’s Aqua and Terra satellites.