According to a new climate report, the coastal and polar regions of the Earth are on thin ice, but San Diego may be in a better place than others to withstand these changes if it works quickly, some authors say.
The Ocean and the Cryosphere in a Changing Climate, released last week by the Intergovernmental Panel on Climate Change, examined the effects of warming on oceans and frozen places.
San Diego struggles with rising sea levels, coastal erosion and sea heat, periods when sea water reaches record high temperatures. However, according to some authors, the natural variability of sea level in the region, ocean temperature and chemical composition can lead to coastal cities remaining ahead of future changes. Understanding the risks specific to San Diego can help.
“Each community has different vulnerabilities, so it’s useful to reduce these risks to specific communities,” said Mark Merrifield, one of the authors of the report and director of the Center for Impacts and Adaptation to Climate Change at the Institute of Oceanography. Sripps in San Diego.
The report notes that, in addition to sustained warming in the ocean, the El Niño and La Nina cycles, as well as the sea heat, caused wild fluctuations in ocean temperature.
“Sea heat, periods of extremely high ocean temperatures, has had a negative impact on marine organisms and ecosystems in all ocean basins over the past two decades, including critical species such as corals, seagrasses and algae,” the report said.
San Diego has experienced this first hand since 2013, when parts of the Pacific Ocean soared to 9 degrees Fahrenheit above normal under the influence of a “drop,” a huge chunk of warm, stagnant water that lingered on the west coast for many years. According to the authors, warm water weakened the normal accumulation of cold, nutrient-rich water from the deep ocean, and the effects spread throughout the region.
“When the waters get warmer and they already are, there are less nutrients, so there’s less phytoplankton,” said Lisa Levine, author of the study and professor of biological oceanography at Scripps. “They are plants of the ocean, they fix carbon and feed the rest of the ocean, so there is less food. It drains through the food web to fish and mammals. And we (saw) some hungry mammals in the last five years. "
Between 2013 and 2017, starving sea lion puppies were in record numbers. “Whales swam closer to shore, where there was more food,” said Rafael Kudela, author of the report and professor of ocean science at the University of California at Santa Cruz. According to him, this is good for whale watching, but bad for whales that run the risk of colliding with ships and sinking closer to the coast.
Changes in temperature pushed some species to the north, so he said market squid, usually the stronghold of southern California, was fished north of San Francisco, while yellowfin tuna moved from Baja California, Mexico, to San Diego. Warmer water has also created the conditions for toxic algal blooms that can cause disgust in animals and humans.
“A large heat wave in 2015 led to the blooming of harmful algae and the closure of the Dangenesse crabs,” on the west coast, Kudela said. “We are concerned that this may become a new normal phenomenon. "We are now beginning another wave of sea heat, so in the spring of 2020 we will see another dangerous flowering of algae?"
In the coming years, marine heatwaves are likely to become more frequent and intense, which “will push some marine organisms, fisheries and ecosystems beyond their sustainability,” the report said. Kelp forests, one of San Diego's characteristic habitats, are vulnerable to changes in water temperature.
But the San Diego coastline is already experiencing seasonal fluctuations in oxygen levels and pH, so some marine life can cope better with climate change by changing the chemistry of the ocean, Levin said.
According to her, along the western coast areas with low oxygen content are a natural feature of the ocean environment. Although many animals avoid the “minimum oxygen zones”, some commercial fish, including the Dover sole and black cod, have learned to live with them.
These low oxygen zones, found at depths of 300 and 3,000 feet, are the result of upwelling cycles common to the coastline of the region. According to Levin, seasonal winds blow over the California coast and froth water that is high in nutrients, but acidic and low in oxygen.
Ocean acidification can interfere with the development of mollusks and affect fish growth. Although this change can have devastating effects on coastal fisheries such as oysters, there is great genetic variation in the ability of different organisms to tolerate it, and some indigenous species are likely to remain stable, Levin said.
Moreover, oxygen and pH levels change during natural events in El Nino and La Nina, Levin said, so Southern California ecosystems are already able to withstand these changes.
“Some species in California are likely to be more tolerant of climate change than species in other parts of the ocean,” Levin said.
According to scientists, while melting ice leads to sea level rise, coastal communities, including San Diego, will experience more frequent and severe flooding. According to the report, runoff from melting glaciers in Greenland and Antarctica, along with the expansion of ocean warming, doubled the global rate of sea level rise.
“The (high) once a century water level will occur annually or more often in many places, and San Diego is one of them,” said Michael Oppenheimer, lead author of the report and professor of geoscience and international studies. affairs at Princeton University.
According to Levin, these consequences are most likely in low-lying areas, such as Imperial Beach, and under certain adverse conditions.
“When the tides interact with the storm surge, we know that there is more flooding on the coast,” she said.
However, most of San Diego’s infrastructure is built at higher elevations, so a region may have a better buffer than areas like San Francisco, where many buildings are built on low-lying areas of reclaimed land, said Merrifield, professor of oceanography at Scripps. ,
“Coastal flooding is certainly a problem in some low-lying areas, but San Diego really benefits from the fact that most of the artificial environment is well above sea level,” he said.
Although San Diego may be more resilient to flooding than some parts of the state, its more immediate threat is bluffing and beach erosion, Merrifield said.
“This may not mean that you will receive a flood, but you will need to pay attention to the conservation of sand on the beach,” he said.
Early warning systems will be important in preventing threats, said So-Min Chong, a professor of geography at the University of Kansas and author of the chapter on risk management.
By more accurately predicting events such as sea heat, officials can control the fishery to prevent overfishing or strengthen marine protected areas to protect existing fish stocks. According to her, planners should work with developers so that new housing can withstand the risks of floods and erosion.
“They need to work with communities, with the construction sector to redesign homes, raise homes and make them waterproof,” Cheong said.
One of the most optimistic notes in the report concerns the role of blue carbon, the restoration of marine plants to help slow down climate change and protect coastlines. Scientists claim that seaweed forests, sea meadows, mangroves and wetlands all absorb carbon, shelter young fish, balance ocean chemistry, and protect inland areas.
“Sea lawns and algae are typically a net carbon sink,” said Kudela. “They regulate the pH of the water, so you don't need to. If we protect these areas and help them expand, we can mitigate the effects of ocean warming and the removal of oxygen. ”
In addition to updating the status of terrestrial oceans and ice, the authors strive to lay out a choice.
“The report really says very clearly that if we act now and take mitigation measures, we can limit the effects of climate change,” Levin said. "And in the future, everything can be very serious and catastrophic, with large losses of life and money, if we do not act."
Climate report describes growing impact on oceans, ice and snow
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Report: San Diego has unique capabilities to tackle climate change (2019, October 9)
restored October 9, 2019
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