There are already signs that the weakening of the Atlantic circulation is having an effect on U.S. fisheries and storms. Ice melting off Greenland as the Arctic warms is believed to play a key role. Credit: NASA
A key question for climate scientists in recent years has been whether the Atlantic Ocean's main circulation system is slowing down, a development that could have dramatic consequences for Europe and other parts of the Atlantic rim. But a new study suggests help may be on the way from an unexpected source -- the Indian Ocean. Think of it as ocean-to-ocean altruism in the age of climate change.
The new study, from Shineng Hu of the Scripps Institution of Oceanography at the University of California-San Diego and Alexey Fedorov of Yale University, appeared recently in the journal Nature Climate Change. It is the latest in a growing body of research that explores how global warming may alter global climate components such as the Atlantic meridional overturning circulation (AMOC). AMOC is one of the planet's largest water circulation systems. It operates like a liquid escalator, delivering warm water to the North Atlantic via an upper limb and sending colder water south via a deeper limb. Although AMOC has been stable for thousands of years, data from the past 15 years, as well as computer model projections, have given some scientists cause for concern. AMOC has showed signs of slowing during that period, but whether it is a result of global warming or only a short-term anomaly related to natural ocean variability is not known and the issue of AMOC stability should not be ignored. The mere possibility that the AMOC could collapse should be a strong reason for concern in an era when human activity is forcing significant changes to the Earth's systems. The last time AMOC weakened substantially was 15,000 to 17,000 years ago, and it had global impacts, like harsh winters in Europe, with more storms or a drier Sahel in Africa due to the downward shift of the tropical rain belt.
Much of Fedorov and Hu's work focuses on specific climate mechanisms and features that may be shifting due to global warming. Using a combination of observational data and sophisticated computer modeling, they plot out what effects such shifts might have over time. For example, Fedorov has looked previously at the role melting Arctic sea ice might have on AMOC. For the new study, they looked at warming in the Indian Ocean. Warming of the Indian Ocean is considered one of the most robust aspects of global warming. The researchers said their modeling indicates a series of cascading effects that stretch from the Indian Ocean all way over to the Atlantic: As the Indian Ocean warms faster and faster, it generates additional precipitation. This, in turn, draws more air from other parts of the world, including the Atlantic, to the Indian Ocean. With so much precipitation in the Indian Ocean, there will be less precipitation in the Atlantic Ocean, the researchers said. Less precipitation will lead to higher salinity in the waters of the tropical portion of the Atlantic -- because there won't be as much rainwater to dilute it. This saltier water in the Atlantic, as it comes north via AMOC, will get cold much quicker than usual and sink faster. "This would act as a jump-start for AMOC, intensifying the circulation," Fedorov said. On the other hand, how long this enhanced Indian Ocean warming will continue is unknown. If other tropical oceans' warming, especially the Pacific, catches up with the Indian Ocean, the advantage for AMOC will stop.
The researchers said this latest finding illustrates the intricate, interconnected nature of global climate. As scientists try to understand the unfolding effects of climate change, they must attempt to identify all of the climate variables and mechanisms that are likely to play a role, they added. There are undoubtedly many other connections that are unknown.
1. Shineng Hu, Alexey V. Fedorov. Indian Ocean warming can strengthen the Atlantic meridional overturning circulation. Nature Climate Change, 2019; DOI: 10.1038/s41558-019-0566-x
Climate change has had extreme impacts in India. Rise in average global temperatures have led to a worrying trend of no rain for long periods and then a sudden bout of excessive rainfall, causing extreme weather events, particularly floods which took lives, destroyed homes and agricultural yields as well as resulted in huge revenue losses. The resulting floods are being exacerbated by unplanned urban growth and environmental degradation, driving millions from their homes and causing widespread damage.
For centuries, Indians have rejoiced at the arrival of the monsoon to break summer’s fever. This year, India’s monsoon season has overrun by almost a month, with unprecedented rainfall causing deaths from collapsing buildings and many crops beginning to rot. Normally the monsoon in north India recedes by the beginning of September, but the average rainfall this month has been 37% above normal. If the situation continues for the remaining few days, it will be the latest the monsoon has ever receded in decades, according to experts in the India Meteorological Department.
The torrential rains that submerged parts of India this year are the latest in a string of major floods in the past decade, some caused by record rainfall - a scenario that many fears could become the “new normal” as climate change increases the frequency of extreme weather. This year, the monsoon arrived late with fierce intensity, where spells of heavy rain have led to flooding in 11 states, taking 1200 lives and displacing millions. India’s summer monsoon has always been variable and has often precipitated floods, especially in the basins of the great Himalayan rivers. But experts say that a combination of global warming, unplanned urban growth, and environmental degradation is increasing flood risk in India.
New studies show that extreme precipitation events are on the rise in large parts of India, especially multi-day deluges that lead to large-scale floods. Warmer temperatures are also speeding up glacier melt in the Himalayas, which is projected to increase flow rates in the Ganges and Brahmaputra Rivers. Last year’s historical floods in the southern state of Kerala were due to the destruction of mountains and hills, as well as development on floodplains and marshes which are exacerbating risks. These floods were caused by extreme rainfall and mismanagement of dam reservoirs, but mining and construction in the Western Ghats, a major hill range, contributed to damaging landslides. The floods in August 2018 took 483 lives, affecting 5.4 million people, and temporarily shut down the state’s new airport, which was built on a floodplain.
One key to preventing or reducing flood damage is understating the shifting contours of the summer monsoon, which brings about 35 inches of rainfall to India every summer. A complex weather system influenced by both global atmospheric circulation and regional meteorological forces, the monsoon is an important piece of the climate puzzle- any change in the system affects the food and water security of billions in the Indian subcontinent, many of them extremely poor.
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© 2019 Oceanographer Daneeja Mawren
Discussion: Astronomical Fall has officially started and with that is a good time to reminisce back on how summer 2019 shaped up! NOAA’s National Center for Environmental Prediction has released their report of climate statistics for this past summer (June 2019-August 2019). The average summer temperature across the contiguous United States was 72.4°F which was 1.0°F above normal and the average minimum temperature was 59.9°F. The minimum temperatures ranked in the upper third of the climate record (1985-2019), coming in 1.5°F above normal since the records were first taken in 1895. The above normal temperature trend occurred in states across the northeastern United States, on the West coast, and in the South. According to NOAA, this summer as a whole rank in the upper third of the climate record. All of the states all experienced near or above average temperatures this summer. No states were below normal. Alaska’s average temperature this summer was 54.6°F, 4.1°F above normal, which marks this summer as the second warmest since 1895. Anchorage, Alaska experienced its warmest summer. The average temperature was 63.2°F. This temperature was 1.8°F higher than the summer of 2004.
The average total of summertime precipitation this year was 8.83 inches, which was above average by 0.51 inches. Since the records began in 1895, this summer also ranked in the top third of the climate record for wettest summer. From the northern Great Plains to the East Coast, many states experienced above average precipitation. States in parts of the Ohio Valley and the Mid-Atlantic region saw much above average precipitation. The opposite could be noted for parts of the western and southern United States. Those regions experienced a summer of below average precipitation. The standout state was Arizona, which experienced its driest summer on record. Other western and southwestern states such as California, New Mexico and Utah all had their tenth driest or lower summer. Utqiagvik, Alaska broke a thirty-year precipitation record. This summer they received 5.43 inches of precipitation breaking the old record of 5.24 inches set in 1989! Now that summer 2019 is in the books, it will be interesting to see how fall shapes up climatologically across the United States.
To check out more climate statistics and interesting facts be sure to click on the following link: https://www.ncdc.noaa.gov/sotc/national/201908
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© 2019 Meteorologist Shannon Scully