Stopping global warming is only way to save Great Barrier Reef, scientists warn

March 16, 2017

The survival of the Great Barrier Reef hinges on urgent moves to cut global warming because nothing else will protect coral from the coming cycle of mass bleaching events, new research has found. The study – which is widely reported by the world’s media today – of three mass bleaching events on Australian reefs in 1998, 2002 and 2016 found coral was damaged by underwater heatwaves regardless of any local improvements to water quality or fishing controls. The research, authored by 46 scientists and published in Nature, raises serious questions about Australia’s long-term conservation plan for its famous reef. The Washington Post says the findings are “sobering”. Prof Terry Hughes, on of the authors, says: “I’m confident that we’ll still have coral reefs if we can keep below 2C. I don’t think we’ll keep below 1.5C… We’re running out of time.” The New York Times has another quote from Hughes: “We didn’t expect to see this level of destruction to the Great Barrier Reef for another 30 years.” The Financial Times, Inside Climate News, Reuters, Associated Press and Time are among the others carrying the story. Carbon Brief also covers the paper’s findings. Joshua Robertson, The Guardian.

Sea Ice Extent Reaches a Low at Both Poles

Arctic sea ice hit a record low wintertime maximum extent in 2017. At 5.57 million square miles, it is the lowest maximum extent in the satellite record, and 455,600 square miles below the 1981 to 2010 average maximum extent.  Credit: NASA Goddard’s Scientific Visualization Studio/L. Perkins

 Arctic sea ice appears to have reached on March 7 a record low wintertime maximum extent, according to scientists at NASA and the NASA-supported National Snow and Ice Data Center (NSIDC) in Boulder, Colorado. And on the opposite side of the planet, on March 3 sea ice around Antarctica hit its lowest extent ever recorded by satellites at the end of summer in the Southern Hemisphere, a surprising turn of events after decades of moderate sea ice expansion.

On Feb. 13, the combined Arctic and Antarctic sea ice numbers were at their lowest point since satellites began to continuously measure sea ice in 1979. Total polar sea ice covered 6.26 million square miles (16.21 million square kilometers), which is 790,000 square miles (2 million square kilometers) less than the average global minimum extent for 1981-2010 — the equivalent of having lost a chunk of sea ice larger than Mexico.

The ice floating on top of the Arctic Ocean and surrounding seas shrinks in a seasonal cycle from mid-March until mid-September. As the Arctic temperatures drop in the autumn and winter, the ice cover grows again until it reaches its yearly maximum extent, typically in March. The ring of sea ice around the Antarctic continent behaves in a similar manner, with the calendar flipped: it usually reaches its maximum in September and its minimum in February.

This winter, a combination of warmer-than-average temperatures, winds unfavorable to ice expansion, and a series of storms halted sea ice growth in the Arctic. This year’s maximum extent, reached on March 7 at 5.57 million square miles (14.42 million square kilometers), is 37,000 square miles (97,00 square kilometers) below the previous record low, which occurred in 2015, and 471,000 square miles (1.22 million square kilometers) smaller than the average maximum extent for 1981-2010.

“We started from a low September minimum extent,” said Walt Meier, a sea ice scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “There was a lot of open ocean water and we saw periods of very slow ice growth in late October and into November, because the water had a lot of accumulated heat that had to be dissipated before ice could grow. The ice formation got a late start and everything lagged behind — it was hard for the sea ice cover to catch up.”

The Arctic’s sea ice maximum extent has dropped by an average of 2.8 percent per decade since 1979, the year satellites started measuring sea ice. The summertime minimum extent losses are nearly five times larger: 13.5 percent per decade. Besides shrinking in extent, the sea ice cap is also thinning and becoming more vulnerable to the action of ocean waters, winds and warmer temperatures.

This year’s record low sea ice maximum extent might not necessarily lead to a new record low summertime minimum extent, since weather has a great impact on the melt season’s outcome, Meier said. “But it’s guaranteed to be below normal.”

In Antarctica, this year’s record low annual sea ice minimum of 815,000 square miles (2.11 million square kilometers) was 71,000 square miles (184,000 square kilometers) below the previous lowest minimum extent in the satellite record, which occurred in 1997.

Antarctic sea ice saw an early maximum extent in 2016, followed by a very rapid loss of ice starting in early September. Since November, daily Antarctic sea ice extent has continuously been at its lowest levels in the satellite record. The ice loss slowed down in February.

This year’s record low happened just two years after several monthly record high sea ice extents in Antarctica and decades of moderate sea ice growth.

“There’s a lot of year-to-year variability in both Arctic and Antarctic sea ice, but overall, until last year, the trends in the Antarctic for every single month were toward more sea ice,” said Claire Parkinson, a senior sea ice researcher at Goddard. “Last year was stunningly different, with prominent sea ice decreases in the Antarctic. To think that now the Antarctic sea ice extent is actually reaching a record minimum, that’s definitely of interest.”

Meier said it is too early to tell if this year marks a shift in the behavior of Antarctic sea ice.

“It is tempting to say that the record low we are seeing this year is global warming finally catching up with Antarctica,” Meier said. “However, this might just be an extreme case of pushing the envelope of year-to-year variability. We’ll need to have several more years of data to be able to say there has been a significant change in the trend.”

NASA/Goddard Space Flight Center. “Sea ice extent sinks to record lows at both poles.” ScienceDaily. ScienceDaily, 22 March 2017. <www.sciencedaily.com/releases/2017/03/170322143149.htm>.

Meanwhile, dead zones caused by polluted runoff are also threatening coral reefs.

Low oxygen conditions were most severe below a certain depth, evident in this photo of dying sponges.

Credit: Arcadio Castillo, STRI

Dead zones affect dozens of coral reefs around the world and threaten hundreds more according to a new study by Smithsonian scientists published in Proceedings of the National Academy of Sciences. Watching a massive coral reef die-off on the Caribbean coast of Panama, they suspected it was caused by a dead zone — a low-oxygen area that snuffs out marine life — rather than by ocean warming or acidification.

“Ocean warming and acidification are recognized global threats to reefs and require large-scale solutions, whereas the newly recognized threats to coral reefs caused by dead zones are more localized, said Andrew Altieri, staff scientist at the Smithsonian Tropical Research Institute and first author of the study. Fortunately dead zones can be reduced by controlling sewage and agricultural runoff into the ocean.”

In September, 2010, coral reefs in Almirante Bay, Bocas del Toro Province, showed severe signs of stress. In addition to corals turning white and dying, which is typical during coral bleaching associated with warming events, there were other clues suggesting that more was involved than high temperatures. Many unusual observations pointed to something else as the culprit. There were thick mats of bacterial slime, and the dead bodies of crabs, sea urchins and sponges lay scattered on the ocean floor. Even more odd, there was a clear depth line above which the reefs looked OK, and below which, something had gone terribly wrong. Even single colonies of corals that straddled the line were fine above and dying below.

Scientists went to work, measuring several aspects of water quality. One set of measurements came back as a shock. Extremely low oxygen levels in deeper waters contrasted with high oxygen levels in shallow waters where corals were still healthy. This is the hallmark of a dead zone.

The team thinks that such dead zones may be common in the tropics but have gone largely unreported, simply because scientists never looked. “The number of dead zones currently on our map of the world is 10 times higher in temperate areas than it is in the tropics, but many marine biologists work out of universities in Europe and North America and are more likely to find dead zones close to home,” Altieri said.

“We were lucky that there was already a reef monitoring program in place at STRI’s Bocas del Toro Research Station as part of the Smithsonian’s Marine Global Earth Observatory Network,” said Rachel Collin, station director.

“Based on our analyses, we think dead zones may be underreported by an order of magnitude.” said Nancy Knowlton, coauthor and Sant Chair for Marine Science at the Smithsonian’s National Museum of Natural History. “For every one dead zone in the tropics, there are probably 10 — nine of which have yet to be identified.”

The researchers found 20 instances when dead zones were implicated in the mass mortality of coral reefs worldwide. “Hypoxia (low oxygen) isn’t even mentioned in several of the most important academic reviews of threats to coral reefs and is rarely discussed at scientific meetings,” Altieri said, “Even worse, many coral-reef monitoring efforts do not include measurement of oxygen levels, making it nearly impossible to identify low oxygen as the cause of mass coral mortality after the fact.” For example, the cause of a 2016 mass mortality at the Flower Garden Reefs in the Gulf of Mexico remains unclear, but some of the photographs look strikingly similar to what was observed in Panama.

The authors argue that building capacity to monitor oxygen on reefs will help people to improve coral reef health and understand how dead zones might interact with other forces such as global warming in a one-two punch, which put reefs in even greater danger.

Materials provided by Smithsonian Tropical Research Institute. Note: Content may be edited for style and length. 

Andrew H. Altieri, Seamus B. Harrison, Janina Seemann, Rachel Collin, Robert J. Diaz, Nancy Knowlton. Tropical dead zones and mass mortalities on coral reefs. Proceedings of the National Academy of Sciences, 2017; 201621517 DOI: 10.1073/pnas.1621517114

Increased atmospheric ammonia over the world’s major agricultural areas is even detectable from space

This map shows global trends in atmospheric ammonia (NH3) as measured from space from 2002 to 2016. Hot colors represent increases due to a combination of increased fertilizer application, reduced scavenging by acid aerosols and climate warming. Cool colors represent decreases due to reduced agricultural burning or fewer wildfires.  Credit: Juying Warner/GRL

The first global, long-term satellite study of airborne ammonia gas has revealed “hotspots” of the pollutant over four of the world’s most productive agricultural regions. Using data from NASA’s Atmospheric Infrared Sounder (AIRS) satellite instrument, the University of Maryland-led research team discovered steadily increasing ammonia concentrations from 2002 to 2016 over agricultural centers in the United States, Europe, China and India. Increased atmospheric ammonia is linked to poor air and water quality.

The study, published March 16, 2017 in the journal Geophysical Research Letters, also describes the probable causes for increased airborne ammonia in each region. Although the specifics vary between areas, the increases in ammonia are broadly tied to crop fertilizers, livestock animal wastes, changes to atmospheric chemistry and warming soils that retain less ammonia. The results could help illuminate strategies to control pollution from ammonia and ammonia byproducts near agricultural areas.

“Our study reports the first global, long-term trends of atmospheric ammonia from space,” said Juying Warner, as associate research scientist in atmospheric and oceanic science at UMD. “Measuring ammonia from the ground is difficult, but the satellite-based method we have developed allows us to track ammonia efficiently and accurately. We hope that our results will help guide better management of ammonia emissions.”

Gaseous ammonia is a natural part of Earth’s nitrogen cycle, but excess ammonia is harmful to plants and reduces air and water quality. In the troposphere — the lowest, densest part of the atmosphere where all weather takes place and where people live — ammonia gas reacts with nitric and sulfuric acids to form nitrate-containing particles that contribute to aerosol pollution that is damaging to human health. Ammonia gas can also fall back to Earth and enter lakes, streams and oceans, where it contributes to harmful algal blooms and “dead zones” with dangerously low oxygen levels.

“Little ammonia comes from tailpipes or smokestacks. It’s mainly agricultural, from fertilizer and animal husbandry,” said Russell Dickerson, a professor of atmospheric and oceanic science at UMD. “It has a profound effect on air and water quality — and ecosystems. Here in Maryland, ammonia from the atmosphere contributes as much as a quarter of the nitrogen pollution in the Chesapeake Bay, causing eutrophication and leading to dead zones that make life very difficult for oysters, blue crabs and other wildlife.”

Each major agricultural region highlighted in the study experienced a slightly different combination of factors that correlate with increased ammonia in the air from 2002 to 2016.

The United States, for example, has not experienced a dramatic increase in fertilizer use or major changes in fertilizer application practices. But Warner, Dickerson and their colleagues found that successful legislation to reduce acid rain in the early 1990s most likely had the unintended effect of increasing gaseous ammonia. The acids that cause acid rain also scrub ammonia gas from the atmosphere, and so the sharp decrease in these acids in the atmosphere is the most plausible explanation for the increase in ammonia over the same time frame.

Europe experienced the least dramatic increase in atmospheric ammonia of the four major agricultural areas highlighted by the study. The researchers suggest this is due in part to successful limits on ammonia-rich fertilizers and improved practices for treating animal waste. Much like the United States, a major potential cause for increased ammonia traces back to reductions in atmospheric acids that would normally remove ammonia from the atmosphere.

“The decrease in acid rain is a good thing. Aerosol loading has plummeted — a substantial benefit to us all,” Dickerson said. “But it has also increased gaseous ammonia loading, which we can see from space.”

In China, a complex interaction of factors is tied to increased atmospheric ammonia. The study authors suggest that efforts to limit sulfur dioxide — a key precursor of sulfuric acid, one of the acids that scrubs ammonia from the atmosphere — could be partially responsible. But China has also greatly expanded agricultural activities since 2002, widening its use of ammonia-containing fertilizers and increasing ammonia emissions from animal waste. Warming of agricultural soils, due at least in part to global climate change, could also contribute.

“The increase in ammonia has spiked aerosol loading in China. This is a major contributor to the thick haze seen in Beijing during the winter, for example,” Warner said. “Also, meat is becoming a more popular component of the Chinese diet. As people shift from a vegetarian to a meat-based diet, ammonia emissions will continue to go up.”

In India, a broad increase in fertilizer use coupled with large contributions from livestock waste have resulted in the world’s highest concentrations of atmospheric ammonia. But the researchers note that ammonia concentrations have not increased nearly as quickly as over other regions. The study authors suggest that this is most likely due to increased emissions of acid rain precursors and, consequently, some increased scrubbing of ammonia from the atmosphere. This leads to increased levels of haze, a dangerous trend confirmed by other NASA satellite instruments, Dickerson said.

In all regions, the researchers attributed some of the increase in atmospheric ammonia to climate change, reflected in warmer air and soil temperatures. Ammonia vaporizes more readily from warmer soil, so as the soils in each region have warmed year by year, their contributions to atmospheric ammonia have also increased since 2002.

The study also ascribes some fluctuations in ammonia to wildfires, but these events are sporadic and unpredictable. As such, the researchers excluded wildfires in their current analysis.

“This analysis has provided the first evidence for some processes we suspected were happening in the atmosphere for some time,” Warner said. “We would like to incorporate data from other sources, such as the Joint Polar Satellite System, in future studies to build a clearer picture.”

Warner, Dickerson and their colleagues hope that a better understanding of atmospheric ammonia will help policy makers craft approaches that better balance the high demand for agriculture with the need for environmental protection.

“As the world’s population grows, so does the demand for food — especially meat,” Dickerson said. “This means farmers and ranchers need more fertilizer, which makes it harder to maintain clean air and water. Wise agricultural practices and reduced greenhouse gas emissions can help avoid adverse effects.”

J. X. Warner, R. R. Dickerson, Z. Wei, L. L. Strow, Y. Wang, Q. Liang. Increased atmospheric ammonia over the world’s major agricultural areas detected from space. Geophysical Research Letters, 2017; DOI: 10.1002/2016GL072305

University of Maryland. “Multi-year study finds ‘hotspots’ of ammonia over world’s major agricultural areas.” ScienceDaily. ScienceDaily, 16 March 2017. www.sciencedaily.com/releases/2017/03/170316112129.htm.

Back to global warming being the only way to slow reef loss, it appears that flowering plants are also vulnerable to global warming:

Researchers have revealed that declining plant diversity — from habitat loss, human use, and other environmental pressures — causes plants to flower earlier, and that the effects of diversity loss on the timing of flowering are similar in magnitude to the effects of global warming. The finding could have a powerful influence on the way scientists study ecosystem changes and measure the effects of global warming.

“Losing species from a system can shift the timing of biological events as much as climate change can,” said Amelia Wolf, a postdoc in the Ecology, Evolution and Environmental Biology (E3B) department at Columbia University and lead author on the study. “Climate change has been shifting the timing of biological events such as flowering, raising concerns about timing mismatches between co-dependent species. This new paper is the first to demonstrate that, in addition to the impact of global warming, we need to be concerned about the ways that species losses are affecting the timing of biological events.”

The paper, entitled “Flowering Phenology Shifts in Response to Biodiversity Loss,” appears in the March issue of Proceedings of the National Academy of Sciences (PNAS).

Since the 1990s, farmers, naturalists and scientists have begun noticing that phenology, or the timing of biological events such as the flowering of plants and the “leafing-out” of trees, is changing, and plants have been flowering progressively earlier than they have in the past. To-date, this observation has been linked to rising temperatures resulting from global warming and, as such, flowering times have been described as a “fingerprint of climate change,” understood as a public, visible, easily-measured display of the detrimental effects of global warming. As a result, numerous observational and experimental studies about the phenological impact of abiotic, physical influences — like global warming — have been conducted and published. There have not, however, been any studies that investigate the phenological impact of an ecosystem’s biotic properties and the way living things interact with each other.

Additionally, there has been a disconnect between the data collected from observational studies, in which researchers observe and analyze what happens naturally in an ecosystem impacted by global warming, and results of experimental studies, where researchers artificially warm a plot in a way that matches natural global warming. The experimental studies consistently fail to produce the same changes to the timing of biological events as those recorded in observational studies.

“The experimental studies aren’t able to account for all of the changes seen in the observational studies,” Wolf said. “It’s possible that part of what those experimental studies aren’t able to account for is the biotic influence — the impact of the other species surrounding those that are flowering. That would mean that it is not just global warming that is producing this effect, but there’s a dual influence of changing temperature and changing species.”

Wolf and her co-researchers set out to see if biodiversity loss had any effect on the timing of biological events. They created a grassland plot in California with 16 different species of plants, and systematically removed species to see what effect it would have on the remaining plants, an experiment that mimics human impact on the composition and diversity of plant communities worldwide. As they reduced plant diversity, the researchers observed warmer ground temperatures, changes in soil resources, and changes in flowering timing. For each species removed, remaining plants flowered, on average, about a half day earlier than they would in the absence of biodiversity loss. Two removed species resulted, on average, in plants flowering a full day earlier than they would otherwise.

The magnitude of this change in flowering timing, Wolf explained, is similar to the magnitude of phenological change previously attributed solely to global warming, which means that the role that biotic interactions — how plants interact with each other — have on phenology is critical to understanding the combined anthropogenic effects on leaf-out, flowering timing and other phenological events, and is something to be considered when studying global climate change. Declining diversity could be contributing to or exacerbating phenological changes attributed to rising global temperatures.

“This is not about when your tulips will reach full bloom, rather biodiversity loss and the impact it has on plant phenology can impact an entire ecosystem,” Wolf said. “Plants flower to reproduce — to create seeds to produce the next generation. A lot of plants rely on insects or birds or some other pollinator to help with this process. For such plants, changes in flowering time could be a really big problem. If a plant flowers before its pollinators are active, the plant species can’t reproduce or may produce fewer seeds. If there are insects, birds, humans, or other animals that are dependent on those plant species, they could be influenced, as well. Plants and the communities in which they grow are interconnected and critically dependent on each other.”

There are many ecological reasons why the timing of flowering matters, Wolf explained, and this new finding introduces a lot of new questions that need to be explored. This study, for example, was conducted in one type of ecosystem, but would researchers see similar patterns in other ecosystems? Wolf suspects they will. Among the other unknowns, the researchers are interested in analyzing which species are most likely to be affected by these biotic interactions; if there are species that are more insulated from the effects; and which species, if lost, result in the most significant changes in the community.

Amelia A. Wolf, Erika S. Zavaleta, Paul C. Selmants. Flowering phenology shifts in response to biodiversity loss. Proceedings of the National Academy of Sciences, 2017; 201608357 DOI: 10.1073/pnas.1608357114

Columbia University. “Biodiversity loss shifts flowering phenology at same magnitude as global warming.” ScienceDaily. ScienceDaily, 24 March 2017. <www.sciencedaily.com/releases/2017/03/170324144535.htm>