Feb 25, 2017 06:45 AM
Air pollution may have masked mid-20th Century sea ice loss
https://www.sciencedaily.com/releases/20...124327.htm
RELEASE: Humans may have been altering Arctic sea ice longer than previously thought, according to researchers studying the effects of air pollution on sea ice growth in the mid-20th Century. The new results challenge the perception that Arctic sea ice extent was unperturbed by human-caused climate change until the 1970s.
Scientists have observed Arctic sea ice loss since the mid-1970s and some climate model simulations have shown the region was losing sea ice as far back as 1950. In a new study, recently recovered Russian observations show an increase in sea ice from 1950 to 1975 as large as the subsequent decrease in sea ice observed from 1975 to 2005. The new observations of mid-century sea ice expansion led researchers behind the new study to the search for the cause.
The new study supports the idea that air pollution is to blame for the observed Arctic sea ice expansion. Particles of air pollution that come primarily from the burning of fossil fuels may have temporarily hidden the effects of global warming in the third quarter of the 20th Century in the eastern Arctic, the researchers say.
These particles, called sulfate aerosols, reflect sunlight back into space and cool the surface. This cooling effect may have disguised the influence of global warming on Arctic sea ice and may have resulted in sea ice growth recorded by Russian aerial surveys in the region from 1950 through 1975, according to the new research.
"The cooling impact from increasing aerosols more than masked the warming impact from increasing greenhouse gases," said John Fyfe, a senior scientist at Environment and Climate Change Canada in Victoria and a co-author of the new study accepted for publication in Geophysical Research Letters, a journal of the American Geophysical Union.
To test the aerosol idea, researchers used computer modeling to simulate sulfate aerosols in the Arctic from 1950 through 1975. Concentrations of sulfate aerosols were especially high during these years before regulations like the Clean Air Act limited sulfur dioxide emissions that produce sulfate aerosols.
The study's authors then matched the sulfate aerosol simulations to Russian observational data that suggested a substantial amount of sea ice growth during those years in the eastern Arctic. The resulting simulations show the cooling contribution of aerosols offset the ongoing warming effect of increasing greenhouse gases over the mid-twentieth century in that part of the Arctic. This would explain the expansion of the Arctic sea ice cover in those years, according to the new study.
Aerosols spend only days or weeks in the atmosphere so their effects are short-lived. The weak aerosol cooling effect diminished after 1980, following the enactment of clean air regulations. In the absence of this cooling effect, the warming effect of long-lived greenhouse gases like carbon dioxide has prevailed, leading to Arctic sea ice loss, according to the study's authors.
The new study helps sort out the swings in Arctic sea ice cover that have been observed over the last 75 years, which is important for a better understanding of sea ice behavior and for predicting its behavior in the future, according to Fyfe.
The new study's use of both observations and modeling is a good way to attribute the Arctic sea ice growth to sulfate aerosols, said Cecilia Bitz, a sea ice researcher at the University of Washington in Seattle who has also looked into the effects of aerosols on Arctic ice. The sea ice record prior to satellite images is "very sparse," added Bitz, who was not involved in the new study.
Bitz also points out that some aerosols may have encouraged sea ice to retreat. Black carbon, for instance, is a pollutant from forest fires and other wood and fossil fuel burning that can darken ice and cause it to melt faster when the sun is up -- the opposite effect of sulfates. Also, black carbon emissions in some parts of the Arctic are still quite common, she said.
Last year's El Niño waves battered California shore to unprecedented degree: 2015-2016 El Niño resulted in severe erosion along Pacific coastline
https://www.sciencedaily.com/releases/20...114751.htm
RELEASE: Last winter's El Niño may have felt weak to residents of Southern California, but it was one of the most powerful weather events of the last 145 years, scientists say.
If severe El Niño events become more common in the future, as some studies suggest, the California coast -- home to more than 25 million people -- may become increasingly vulnerable to coastal hazards, independently of projected sea level rise.
A new study conducted by scientists at the University of California Santa Barbara (UCSB) and colleagues at several other institutions found that during the 2015-2016 El Niño, winter beach erosion on the Pacific coast was 76 percent above normal. Most beaches in California were eroded beyond historical extremes, the study found.
The results appear this week in the journal Nature Communications.
"Infrequent and extreme events can be extremely damaging to coastal marine habitats and communities," said David Garrison, a program director in the National Science Foundation's Division of Ocean Sciences, which funded the research. "While this paper stresses the effect of waves and sediment transport on beach structure, organisms living on and in the sediment will also be profoundly affected."
Added David Hubbard, a UCSB marine ecologist and paper co-author: "This study illustrates the value of broad regional collaboration using long-term data for understanding coastal ecosystem responses to environmental change. We really need this scale of data on coastal processes to understand what's going on with the ecology of the coast."
While winter beach erosion -- the removal and loss of sand from the beach -- is a normal seasonal process, during El Niño events the extent of erosion can be more severe.
The research team assessed seasonal beach behavior for 29 beaches along more than 1,200 miles of the Pacific coast. They made 3-D surface maps and cross-shore profiles using aerial LIDAR (Light Detection and Ranging), GPS topographic surveys and direct measurements of sand quantities. They then combined that information with wave and water-level data from each beach between 1997 and 2016.
"Wave conditions and coastal response were unprecedented for many locations during the winter of 2015-16," said Patrick Barnard, lead author of the paper and a geologist with the U.S. Geological Survey. "The winter wave energy equaled or exceeded measured historical maximums along the West Coast, corresponding to extreme beach erosion across the region."
The 2015-2016 El Niño was one of the strongest ever recorded.
However, that most recent El Niño was largely considered a dud from a water resources perspective due to unusually low rainfall, particularly in Southern California, which received 70 percent less rain than during the last two big El Niño events.
"The waves that attacked our coast, generated from storms across the North Pacific, were exceptional and among the largest ever recorded," Hubbard said. "But the lack of rainfall means that coastal rivers produced very little sand to fill in what was lost from the beaches, so recovery has been slow."
Rivers are the primary suppliers of sand to California beaches, despite long-term water reductions in the 20th century due to extensive dam construction. California's extreme drought resulted in lower river flows, which in turn equated to less sand being carried to the coast to help sustain beaches.
While most beaches in the survey eroded beyond historical extremes, some fared better than others. The condition of the beach before the winter of 2015 strongly influenced the severity of the erosion and the ability to recover afterward through natural replenishment processes.
Mild wave activity in the Pacific Northwest as well as artificial augmentation of beaches (adding sand) in Southern California prior to the winter of 2015-2016 prevented some areas from eroding beyond historical extremes.
"We need to understand these challenges, which include rising sea level and the fact that most of the problems occur during these peak El Niño events," Hubbard said. "Then we need to restore and manage our coasts in ways that will enable us to deal with these events and conserve beach ecosystems."
Warming temperatures could trigger starvation, extinctions in deep oceans
https://www.sciencedaily.com/releases/20...092415.htm
RELEASE: Researchers from 20 of the world's leading oceanographic research centers today warned that the world's largest habitat -- the deep ocean floor -- may face starvation and sweeping ecological change by the year 2100.
Warming ocean temperatures, increased acidification and the spread of low-oxygen zones will drastically alter the biodiversity of the deep ocean floor from 200 to 6,000 meters below the surface. The impact of these ecosystems to society is just becoming appreciated, yet these environments and their role in the functioning of the planet may be altered by these sweeping impacts.
Results of the study, which was supported by the Foundation Total and other organizations, were published this week in the journal Elementa.
"Biodiversity in many of these areas is defined by the meager amount of food reaching the seafloor and over the next 80-plus years -- in certain parts of the world -- that amount of food will be cut in half," said Andrew Thurber, an Oregon State University marine ecologist and co-author on the study. "We likely will see a shift in dominance to smaller organisms. Some species will thrive, some will migrate to other areas, and many will die.
"Parts of the world will likely have more jellyfish and squid, for example, and fewer fish and cold water corals."
The study used the projections from 31 earth system models developed for the Intergovernmental Panel on Climate Change to predict how the temperature, amount of oxygen, acidity (pH) and food supply to the deep-sea floor will change by the year 2100. The authors found these models predict that deep ocean temperatures in the "abyssal" seafloor (3,000 to 6,000 meters deep) will increase as much as 0.5 to 1.0 degrees (Celsius) in the North Atlantic, Southern and Arctic oceans by 2100 compared to what they are now.
Temperatures in the "bathyal" depths (200 to 3,000 meters deep) will increase even more -- parts of this deep-sea floor are predicted to see an increase of nearly 4 degrees © in the Pacific, Atlantic and Arctic oceans.
"While four degrees doesn't seem like much on land, that is a massive temperature change in these environments," Thurber said. "It is the equivalent of having summer for the first time in thousands to millions of years."
The over-arching lack of food will be exacerbated by warming temperatures, Thurber pointed out.
"The increase in temperature will increase the metabolism of organisms that live at the ocean floor, meaning they will require more food at a time when less is available."
Most of the deep sea already experiences a severe lack of food, but it is about to become a famine, according to Andrew Sweetman, a researcher at Heriot-Watt University in Edinburgh and lead author on the study.
"Abyssal ocean environments, which are over 3,000 meters deep, are some of the most food-deprived regions on the planet," Sweetman said. "These habitats currently rely on less carbon per meter-squared each year than is present in a single sugar cube. Large areas of the abyss will have this tiny amount of food halved and for a habitat that covers half the Earth, the impacts of this will be enormous."
The impacts on the deep ocean are unlikely to remain there, the researchers say. Warming ocean temperatures are expected to increase stratification in some areas yet increase upwelling in others. This can change the amount of nutrients and oxygen in the water that is brought back to the surface from the deep sea. This low-oxygen water can affect coastal communities, including commercial fishing industries, which harvest groundfish from the deep sea globally and especially in areas like the Pacific Coast of North America, Thurber said.
"A decade ago, we even saw low-oxygen water come shallow enough to kill vast numbers of Dungeness crabs," Thurber pointed out. "The die-off was massive."
Areas most likely to be affected by the decline in food are the North and South Pacific, North and South Atlantic, and North and South Indian oceans.
"The North Atlantic in particular will be affected by warmer temperatures, acidification, a lack of food and lower oxygen," Thurber said. "Water in the region is soaking up the carbon from the atmosphere and then sending it on its path around the globe, so it likely will be the first to feel the brunt of the changes."
Thurber, who is a faculty member in Oregon State's College of Earth, Ocean, and Atmospheric Sciences, has previously published on the "services" or benefits provided by the deep ocean environments. The deep sea is important to many of the processes affecting the Earth's climate, including acting as a "sink" for greenhouse gases and helping to offset growing amounts of carbon dioxide emitted into the atmosphere.
These habitats are not only threatened by warm temperatures and increasing carbon dioxide; they increasingly are being used by fishing and explored by mining industries for extraction of mineral resources.
"If we look back in Earth's history, we can see that small changes to the deep ocean caused massive shifts in biodiversity," Thurber said. "These shifts were driven by those same impacts that our model predict are coming in the near future. We think of the deep ocean as incredibly stable and too vast to impact, but it doesn't take much of a deviation to create a radically altered environment.
https://www.sciencedaily.com/releases/20...124327.htm
RELEASE: Humans may have been altering Arctic sea ice longer than previously thought, according to researchers studying the effects of air pollution on sea ice growth in the mid-20th Century. The new results challenge the perception that Arctic sea ice extent was unperturbed by human-caused climate change until the 1970s.
Scientists have observed Arctic sea ice loss since the mid-1970s and some climate model simulations have shown the region was losing sea ice as far back as 1950. In a new study, recently recovered Russian observations show an increase in sea ice from 1950 to 1975 as large as the subsequent decrease in sea ice observed from 1975 to 2005. The new observations of mid-century sea ice expansion led researchers behind the new study to the search for the cause.
The new study supports the idea that air pollution is to blame for the observed Arctic sea ice expansion. Particles of air pollution that come primarily from the burning of fossil fuels may have temporarily hidden the effects of global warming in the third quarter of the 20th Century in the eastern Arctic, the researchers say.
These particles, called sulfate aerosols, reflect sunlight back into space and cool the surface. This cooling effect may have disguised the influence of global warming on Arctic sea ice and may have resulted in sea ice growth recorded by Russian aerial surveys in the region from 1950 through 1975, according to the new research.
"The cooling impact from increasing aerosols more than masked the warming impact from increasing greenhouse gases," said John Fyfe, a senior scientist at Environment and Climate Change Canada in Victoria and a co-author of the new study accepted for publication in Geophysical Research Letters, a journal of the American Geophysical Union.
To test the aerosol idea, researchers used computer modeling to simulate sulfate aerosols in the Arctic from 1950 through 1975. Concentrations of sulfate aerosols were especially high during these years before regulations like the Clean Air Act limited sulfur dioxide emissions that produce sulfate aerosols.
The study's authors then matched the sulfate aerosol simulations to Russian observational data that suggested a substantial amount of sea ice growth during those years in the eastern Arctic. The resulting simulations show the cooling contribution of aerosols offset the ongoing warming effect of increasing greenhouse gases over the mid-twentieth century in that part of the Arctic. This would explain the expansion of the Arctic sea ice cover in those years, according to the new study.
Aerosols spend only days or weeks in the atmosphere so their effects are short-lived. The weak aerosol cooling effect diminished after 1980, following the enactment of clean air regulations. In the absence of this cooling effect, the warming effect of long-lived greenhouse gases like carbon dioxide has prevailed, leading to Arctic sea ice loss, according to the study's authors.
The new study helps sort out the swings in Arctic sea ice cover that have been observed over the last 75 years, which is important for a better understanding of sea ice behavior and for predicting its behavior in the future, according to Fyfe.
The new study's use of both observations and modeling is a good way to attribute the Arctic sea ice growth to sulfate aerosols, said Cecilia Bitz, a sea ice researcher at the University of Washington in Seattle who has also looked into the effects of aerosols on Arctic ice. The sea ice record prior to satellite images is "very sparse," added Bitz, who was not involved in the new study.
Bitz also points out that some aerosols may have encouraged sea ice to retreat. Black carbon, for instance, is a pollutant from forest fires and other wood and fossil fuel burning that can darken ice and cause it to melt faster when the sun is up -- the opposite effect of sulfates. Also, black carbon emissions in some parts of the Arctic are still quite common, she said.
Last year's El Niño waves battered California shore to unprecedented degree: 2015-2016 El Niño resulted in severe erosion along Pacific coastline
https://www.sciencedaily.com/releases/20...114751.htm
RELEASE: Last winter's El Niño may have felt weak to residents of Southern California, but it was one of the most powerful weather events of the last 145 years, scientists say.
If severe El Niño events become more common in the future, as some studies suggest, the California coast -- home to more than 25 million people -- may become increasingly vulnerable to coastal hazards, independently of projected sea level rise.
A new study conducted by scientists at the University of California Santa Barbara (UCSB) and colleagues at several other institutions found that during the 2015-2016 El Niño, winter beach erosion on the Pacific coast was 76 percent above normal. Most beaches in California were eroded beyond historical extremes, the study found.
The results appear this week in the journal Nature Communications.
"Infrequent and extreme events can be extremely damaging to coastal marine habitats and communities," said David Garrison, a program director in the National Science Foundation's Division of Ocean Sciences, which funded the research. "While this paper stresses the effect of waves and sediment transport on beach structure, organisms living on and in the sediment will also be profoundly affected."
Added David Hubbard, a UCSB marine ecologist and paper co-author: "This study illustrates the value of broad regional collaboration using long-term data for understanding coastal ecosystem responses to environmental change. We really need this scale of data on coastal processes to understand what's going on with the ecology of the coast."
While winter beach erosion -- the removal and loss of sand from the beach -- is a normal seasonal process, during El Niño events the extent of erosion can be more severe.
The research team assessed seasonal beach behavior for 29 beaches along more than 1,200 miles of the Pacific coast. They made 3-D surface maps and cross-shore profiles using aerial LIDAR (Light Detection and Ranging), GPS topographic surveys and direct measurements of sand quantities. They then combined that information with wave and water-level data from each beach between 1997 and 2016.
"Wave conditions and coastal response were unprecedented for many locations during the winter of 2015-16," said Patrick Barnard, lead author of the paper and a geologist with the U.S. Geological Survey. "The winter wave energy equaled or exceeded measured historical maximums along the West Coast, corresponding to extreme beach erosion across the region."
The 2015-2016 El Niño was one of the strongest ever recorded.
However, that most recent El Niño was largely considered a dud from a water resources perspective due to unusually low rainfall, particularly in Southern California, which received 70 percent less rain than during the last two big El Niño events.
"The waves that attacked our coast, generated from storms across the North Pacific, were exceptional and among the largest ever recorded," Hubbard said. "But the lack of rainfall means that coastal rivers produced very little sand to fill in what was lost from the beaches, so recovery has been slow."
Rivers are the primary suppliers of sand to California beaches, despite long-term water reductions in the 20th century due to extensive dam construction. California's extreme drought resulted in lower river flows, which in turn equated to less sand being carried to the coast to help sustain beaches.
While most beaches in the survey eroded beyond historical extremes, some fared better than others. The condition of the beach before the winter of 2015 strongly influenced the severity of the erosion and the ability to recover afterward through natural replenishment processes.
Mild wave activity in the Pacific Northwest as well as artificial augmentation of beaches (adding sand) in Southern California prior to the winter of 2015-2016 prevented some areas from eroding beyond historical extremes.
"We need to understand these challenges, which include rising sea level and the fact that most of the problems occur during these peak El Niño events," Hubbard said. "Then we need to restore and manage our coasts in ways that will enable us to deal with these events and conserve beach ecosystems."
Warming temperatures could trigger starvation, extinctions in deep oceans
https://www.sciencedaily.com/releases/20...092415.htm
RELEASE: Researchers from 20 of the world's leading oceanographic research centers today warned that the world's largest habitat -- the deep ocean floor -- may face starvation and sweeping ecological change by the year 2100.
Warming ocean temperatures, increased acidification and the spread of low-oxygen zones will drastically alter the biodiversity of the deep ocean floor from 200 to 6,000 meters below the surface. The impact of these ecosystems to society is just becoming appreciated, yet these environments and their role in the functioning of the planet may be altered by these sweeping impacts.
Results of the study, which was supported by the Foundation Total and other organizations, were published this week in the journal Elementa.
"Biodiversity in many of these areas is defined by the meager amount of food reaching the seafloor and over the next 80-plus years -- in certain parts of the world -- that amount of food will be cut in half," said Andrew Thurber, an Oregon State University marine ecologist and co-author on the study. "We likely will see a shift in dominance to smaller organisms. Some species will thrive, some will migrate to other areas, and many will die.
"Parts of the world will likely have more jellyfish and squid, for example, and fewer fish and cold water corals."
The study used the projections from 31 earth system models developed for the Intergovernmental Panel on Climate Change to predict how the temperature, amount of oxygen, acidity (pH) and food supply to the deep-sea floor will change by the year 2100. The authors found these models predict that deep ocean temperatures in the "abyssal" seafloor (3,000 to 6,000 meters deep) will increase as much as 0.5 to 1.0 degrees (Celsius) in the North Atlantic, Southern and Arctic oceans by 2100 compared to what they are now.
Temperatures in the "bathyal" depths (200 to 3,000 meters deep) will increase even more -- parts of this deep-sea floor are predicted to see an increase of nearly 4 degrees © in the Pacific, Atlantic and Arctic oceans.
"While four degrees doesn't seem like much on land, that is a massive temperature change in these environments," Thurber said. "It is the equivalent of having summer for the first time in thousands to millions of years."
The over-arching lack of food will be exacerbated by warming temperatures, Thurber pointed out.
"The increase in temperature will increase the metabolism of organisms that live at the ocean floor, meaning they will require more food at a time when less is available."
Most of the deep sea already experiences a severe lack of food, but it is about to become a famine, according to Andrew Sweetman, a researcher at Heriot-Watt University in Edinburgh and lead author on the study.
"Abyssal ocean environments, which are over 3,000 meters deep, are some of the most food-deprived regions on the planet," Sweetman said. "These habitats currently rely on less carbon per meter-squared each year than is present in a single sugar cube. Large areas of the abyss will have this tiny amount of food halved and for a habitat that covers half the Earth, the impacts of this will be enormous."
The impacts on the deep ocean are unlikely to remain there, the researchers say. Warming ocean temperatures are expected to increase stratification in some areas yet increase upwelling in others. This can change the amount of nutrients and oxygen in the water that is brought back to the surface from the deep sea. This low-oxygen water can affect coastal communities, including commercial fishing industries, which harvest groundfish from the deep sea globally and especially in areas like the Pacific Coast of North America, Thurber said.
"A decade ago, we even saw low-oxygen water come shallow enough to kill vast numbers of Dungeness crabs," Thurber pointed out. "The die-off was massive."
Areas most likely to be affected by the decline in food are the North and South Pacific, North and South Atlantic, and North and South Indian oceans.
"The North Atlantic in particular will be affected by warmer temperatures, acidification, a lack of food and lower oxygen," Thurber said. "Water in the region is soaking up the carbon from the atmosphere and then sending it on its path around the globe, so it likely will be the first to feel the brunt of the changes."
Thurber, who is a faculty member in Oregon State's College of Earth, Ocean, and Atmospheric Sciences, has previously published on the "services" or benefits provided by the deep ocean environments. The deep sea is important to many of the processes affecting the Earth's climate, including acting as a "sink" for greenhouse gases and helping to offset growing amounts of carbon dioxide emitted into the atmosphere.
These habitats are not only threatened by warm temperatures and increasing carbon dioxide; they increasingly are being used by fishing and explored by mining industries for extraction of mineral resources.
"If we look back in Earth's history, we can see that small changes to the deep ocean caused massive shifts in biodiversity," Thurber said. "These shifts were driven by those same impacts that our model predict are coming in the near future. We think of the deep ocean as incredibly stable and too vast to impact, but it doesn't take much of a deviation to create a radically altered environment.
