When Harvey made landfall along the Middle Texas Coast it was the first major hurricane to make landfall in the United States since 2005 and the first hurricane to make landfall in that area since Celia in 1970. Harvey was epic in the amount of rain that fell on Houston, because the storm stalled over the city. Hurricane Harvey was followed by Irma a hurricane that reached Category 5 storm status before it crashed through the Caribbean. The islands of Barbuda, St. Martin, St Barthelemy (St Barts), Anguilla were crushed by the storm and others like Puerto Rico were impacted before Irma arrived in Florida with storm surge that knocked out power to 15 million people.
The National Oceanic and Atmospheric Administration (NOAA) had predicted that 2017 would be an above –average year for Atlantic storms and I’m a believer. One of the reasons that NOAA made this prediction is that since 1990 we have been in the warm phase of the Atlantic Multidecadal Oscillation (AMO). The AMO is an series of long-duration changes in the sea surface temperature that have been observed in the North Atlantic Ocean, with a difference of about 1°F between the cool and warm phases that may last for 20-40 years at a time.
These temperature changes in the cycle are natural. Scientists first detected the AMO in 1994 using the ocean temperature measurement from the last 150 years; however, studies of paleoclimate proxies, such as tree rings and ice cores, have shown that oscillations similar to those observed have been occurring for at least the last millennium. This is clearly longer than modern man has been affecting climate, so the AMO is probably a natural climate oscillation.
In the 20th century, the climate swings of the AMO have alternately camouflaged and exaggerated the effects of changing climate, and made attribution of global warming more difficult to ascertain. Nonetheless we know that during the warm phase of the AMO, the numbers of tropical storms that mature into severe hurricanes is at least twice the rate than during the cool phase. Since the AMO switched to its warm phase around 1995, severe hurricanes have become much more frequent.
Scientists do not know enough to predict exactly when the AMO will switch to the cooler phase. Computer models are far from being able to do this and the climate models are useless here. What is possible to do at present is to calculate the probability that a change in the AMO will occur within a given future time frame. The AMO affects rainfall in Europe, drought in the Amazon, and Atlantic hurricanes. The warm phase fuels storms by warming the tropical Atlantic and intensifying the West African monsoon. The monsoon spins up low-pressure systems that enter the tropical Atlantic and allows the storms that form there to develop rotation and gain energy.
Reporters have invariably attributed the recent storms to climate change. However, most of the impacts predicted by scientists for climate change are still out in the future and of a much bigger scale. So far, scientists tell us that over the past century the oceans have risen over 7 inches which has caused an increase in the frequency of flooding, but may not have had any other effect. According to some ocean researchers the AMO is now close to neutral or about to switch. However, other scientists believe that factors outside the ocean may also trigger changes in the AMO. Studies of paleoclimate proxies indicate that volcanic eruptions and small changes in the sun’s output may have warmed and cooled the ocean and triggered AMO reversals.
In the last few decades of our planet’s history, humans have added their own influences, such as particulates from burning coal, which reflect sunlight thereby having a cooling effect on the ocean. Some scientists attribute particulates from burning coal in the second half of the 20th century as the primary cause of the most recent cold phase of the AMO, which lasted from 1970 to 1994. Still others propose that increased greenhouse gasses in the atmosphere and declining air pollution might prolong the current warm period of the AMO. We don’t know. We are still learning about our planet even as it changes.
We do know that in the past half century our cities have continue to build and expand into historic flood zones while sea level was rising. This trend has been encouraged by government policy decisions. Since the 1960’s the United Stated government has provide cheap, subsidized flood insurance that has encouraged development in areas of high flood risk that has often resulted in the elimination of the flood plain buffers zones.
It is simply not feasible to protect all of the coastal lands from rising oceans and storm surges or to continually rebuild properties that repeatedly flood. Before Harvey the flood insurance program was already $24 billion in debt. Sooner or later areas of the coast will have to be abandoned, because we will be unable to stop the impacts of a changing climate.
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