Extreme Weather

March 22, 2010

Expect bigger, and possibly more, storms with climate change

Never has a cliché been more apt: the evening of February 25, 2010 was indeed a dark and stormy night as high winds and torrential rains swept across the Gulf of Maine. Gusts of over 65 mph (104 kph) were recorded by data buoys in the Gulf and wave heights reached 30 feet (9 meters).

Ashore, the storm caused significant damage as trees were toppled, power lines downed and roads washed out. Parts of the coast were inundated as waves, winds and tides combined to drive sea water into low lying areas. All told, the storm was one of the worst experienced by the region in many years. Certainly the storm was an extreme weather event – and climate change makes it likely that we will see more and more such storms in the coming years.

Experts say the Blizzard of ’78 was the Massachusetts “Storm of the Century.” It dumped 27.1 inches of snow on Boston on February 6 and 7, bringing the city and surrounding suburbs to a halt for a week. The tides were devastating. At its peak, the ocean rose 15.2 feet above mean low water (measured at the Boston Tide Station). Ninety-nine people died and thousands of homes and businesses were destroyed or severely damaged, with damage exceeding $2.3 billion (in 1998 dollars). This house was completely split by the storm.

Globally, reports of natural disasters have increased exponentially in the past 100 years. This is due in large part to the fact that such events are measured by their effect on people and the built environment. The dark part of a dark and stormy night takes on new meaning when it refers to power outages. The February 25 storm resulted in reports of hundreds of thousands of homes without power. Seawalls collapsed, jetties were undermined, docks washed away, and boats lost.

The number of damaging storms reported globally is a function of population growth, especially since such growth is occurring disproportionately in coastal areas. If a storm occurs and no one notices, it’s a bit like the proverbial tree falling in the forest. As a result, historical records of storms are sketchy, populations were smaller and the landscape less engineered. Also, the ability to record, transmit and collect storm data was somewhat limited before the era of satellites and the internet.

To sort out the effect of population growth, improvements in data collection and climate change on trends in disaster reports, Pascal Peduzzi, of the United Nations Environment Programme, compared 100 years of global reports of earthquakes to those of floods and hurricanes. Both records increase beginning in the mid-20th century in a fashion that could be explained by population growth and the improved flow of information from affected sites to global databases.

But reports of hurricanes and floods have increased far faster. Because earthquakes are unlikely to be affected by climate change, Peduzzi concludes that increasing frequency of storms due to climate change is a factor in the rise of storm damage reports.

With such evidence, Peducci warns that “the failure to introduce measures to combat global warming may rebound, with victims sending in the bill much as they did in the United States when they took the tobacco industry to court.”

The arrows in this image indicate the direction and speed of the wind in a typical nor’easter. Image courtesy of the Gulf of Maine Ocean Observing System, www.gomoos.org.

In a study published earlier this year in the journal Nature Geoscience, researchers suggest that, globally, climate change will result in approximately the same number of storms annually but that these storms will be stronger and will result in a 20 percent increase in precipitation.

The authors, lead by Thomas Knutson of the National Oceanic and Atmospheric Administration’s Geophysical Fluid Dynamics Laboratory in Princeton, New Jersey, stress the difficulty of making accurate predictions about the frequency of storms, particularly for subregions of the globe, noting that for such areas “there is much more uncertainty in projections….with changes of up to +50 percent or more projected by models.”

The problem arises from the fact that models of future storm activity are based on analysis of past storm data. In theory, the longer the time period reviewed, the better the model. Knutson et al’s analysis of data from the Atlantic Ocean illustrates the problem. Storm data from a variety of studies, including analysis of a 1,500-year record of sediment outwash at sites along the east coast and hurricane counts from the late 1800s to the present, are subject to errors in observation and analysis. For example, the relationship between sediment outwash and hurricanes may not be straightforward and hurricanes have been counted using changing criteria over the years.

In the last 50 years, when data collection has been more reliable, the increasing trend in the number of hurricanes correlates well with the increasing trend in sea surface temperature. This model, which assumes that sea surface temperatures are driven by climate change, is the basis, in part, of the scientific consensus that the frequency and intensity of storms in the Northwest Atlantic will increase.

Storms that roil the Gulf of Maine originate from two tracks. The first track brings low pressure systems into the region from the west. The second track brings low pressure systems up the Atlantic seaboard. Such systems draw their strength from the warm waters of the tropics and spin in a counter-clockwise direction. They are classified according to their wind strength: tropical storms have winds between 39 and 73 mph (63 and 117 kph) and hurricanes blow at 74 mph (118 kph) or greater. (The generic term for a hurricane is a cyclone. Such storms are known as hurricanes in the North Atlantic, typhoons in the North Pacific and cyclones elsewhere.) When a high pressure system from the north converges on the Gulf of Maine at the same time as a tropical storm or hurricane from the south, a particularly powerful storm, known as a nor’easter, results.

A satellite image of the “perfect storm”, October, 1991. Image courtesy of the National Climate Data Center, www.ncdc.noaa.gov.

Sebastian Junger’s bestselling book, The Perfect Storm, made famous the story of such a storm that raged across the Northwest Atlantic in the fall of 1991 and the resulting tragic loss of a fishing vessel and its crew of six hands. In the process, Junger created a powerful metaphor now used to describe any number of situations where the intersection of events results in catastrophe. But its first use is perhaps most apt and describes one example of extreme weather events that are likely to increase in frequency and intensity in the Gulf of Maine.

In November of 1898, a similar storm created havoc in the Gulf of Maine region. Among the estimated 400 vessels that were lost in the storm was the steamship Portland — nearly 200 lost their lives as the vessel sank on Stellwagen Bank in the western Gulf of Maine. The ship appeared to have disappeared without a trace until Stellwagen was designated as a National Marine Sanctuary in 1992. Researchers identified the wreck within the boundaries of the sanctuary and put together the story of its loss based on the wreck and accounts of the storm.

Big storms are also known as “bombs” and “gullywashers,” graphic descriptions of the power and effect they have as they rip through the region. On the morning of February 26, the ground was everywhere littered with branches and in some areas trees had fallen like so many match sticks – “bomb” seemed an appropriate description for what had happened. Rivers and streams flooded their banks as the several inches of rain dumped on the Gulf watershed found its way to the ocean. Rain fell too fast to be absorbed by soils and storm water control systems; and washed whatever it found in its path into the Gulf.

Sediment-laden plumes were visible at the mouths of rivers and thousands of acres of shellfish flats were closed. Because “gullywashers” transport animal wastes and sewage overflows to marine waters, major rain events trigger automatic closures. Shellfish harvesters will have fewer days in which to make their living as growing numbers of storms move through the area. Storms may cause additional problems for harvesters as freshwater runoff is thought to contribute to the conditions that trigger blooms of the toxic phytoplankton that cause red tides. If winds are in the right direction, however, storms can work in their favor, holding blooms offshore.

It seems as though new records for extreme weather events are being made with each turn of the seasons. In 2008, spring flooding along the Saint John was the worst in 35 years. Eight of the 10 wettest years on record in the Gulf of Maine region have occurred since 1970. In February 2009 a storm classified by meteorologists as a “mega weather bomb” was described as the worst in a generation to hit New Brunswick. In Portland, Maine the rate of warming in mean annual air temperature during recent decades is more than double the rate of warming observed over the past 120 years. In Atlantic Canada the summer of 2009 was the wettest since record-keeping began 63 years ago.

A record of wave heights recorded on data buoys in the Gulf of Maine during a storm in late February. Data courtesy of the Gulf of Maine Ocean Observing System, www.gomoos.org.

Joe Pelczarski, who tracks extreme weather events for the Massachusetts Office of Coastal Zone Management, says nor’easters are particularly damaging storms for the Gulf of Maine because they tend to move more slowly than hurricanes. According to Pelczarski, “Nor’easters can linger longer and are therefore more likely to coincide with high tide” resulting in storm surges that threaten coastal areas.

A monster nor’easter in the spring of 2008 resulted in a damaging storm surge throughout the Gulf of Maine as it coincided with spring high tides. Pelczarski analyzed over 100 years’ worth of data from the Boston tide gauge and discovered that the frequency of exceptionally high tides has risen considerably over that period. Sea level rise and storms, both affected by climate change, are most likely the cause. In any case, rising high tides portend more damage from coastal storms.

Today, storm watching has taken on new meaning as, along with scientists, citizens consider how climate change may be affecting our weather. A warm day in winter, snow in April, a string of big storms, a chillier than average summer, any weather event deemed out of the ordinary, is fodder for the ongoing debate regarding climate change, a debate conducted simultaneously in conference rooms and agency meetings as well as in the vicinity of the water cooler, around the dinner table, and at the coffee shop.

Climate scientists consistently and repeatedly remind the rest of us that the weather is not the same thing as the climate. Weather is what happens day-to-day; climate is a long-term average of the weather. Weather is much more variable than climate. Any given weather event, such as a snowstorm in April, tells us nothing about the climate. Even putting together several years of personal experience with weather leaves us short of the mark in describing climate.

Heather Deese, Director of Marine Programs for the Island Institute in Rockland, Maine, is working on two efforts to put today’s weather in climate perspective. One is an ongoing conversation with fishermen about the relationship of their observations regarding storms and other weather events to the longer term climate record. The second is a new program that, once funded, will enable elementary school children on Maine’s islands to track weather patterns and match them to long-term averages.

Fishing boat strains at mooring in Portland Harbor, Maine, during Patriot’s Day storm of 2007. (Photo, Petri Tuohimaa.)

“The year-to-year and decade-to-decade variability of storms is so much greater than the long-term variability. In terms of our own personnel experience, it is hard to observe long-term trends, to observe the reality of climate change,” says Deese. “Our goal is to have school kids learn about the difference between weather and climate. And to learn from people in their towns about what storms mean for their communities.”

By understanding the context of extreme weather events, individuals, communities, states and provinces can better prepare for the future of life on the water and on the coast.


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