Observed Climate Change
©ADAM HUNGER/Reuters/Corbis
Between 1895 and 2011, temperatures in the Northeast increased by almost 2˚F (0.16˚F per decade), and precipitation increased by approximately five inches, or more than 10% (0.4 inches per decade).4 Coastal flooding has increased due to a rise in sea level of approximately 1 foot since 1900. This rate of sea level rise exceeds the global average of approximately 8 inches (see Ch. 2: Our Changing Climate, Key Message 10; Ch. 25: Coasts), due primarily to land subsidence,5 although recent research suggests that changes in ocean circulation in the North Atlantic – specifically, a weakening of the Gulf Stream – may also play a role.6
The Northeast has experienced a greater recent increase in extreme precipitation than any other region in the United States; between 1958 and 2010, the Northeast saw more than a 70% increase in the amount of precipitation falling in very heavy events (defined as the heaviest 1% of all daily events) (see Ch. 2: Our Changing Climate, Figure 2.18).7
Projected Climate Change
As in other areas, the amount of warming in the Northeast will be highly dependent on global emissions of heat-trapping gases. If emissions continue to increase (as in the A2 scenario), warming of 4.5ºF to 10ºF is projected by the 2080s; if global emissions were reduced substantially (as in the B1 scenario), projected warming ranges from about 3ºF to 6ºF by the 2080s.4
Under both emissions scenarios, the frequency, intensity, and duration of heat waves is expected to increase, with larger increases under higher emissions (Ch. 2: Our Changing Climate). Much of the southern portion of the region, including the majority of Maryland and Delaware, and southwestern West Virginia and New Jersey, are projected by mid-century to experience many more days per year above 90°F compared to the end of last century under continued increases in emissions (Figure 16.2, A2 scenario). This will affect the region’s vulnerable populations, infrastructure, agriculture, and ecosystems.
The frequency, intensity, and duration of cold air outbreaks is expected to decrease as the century progresses, although some research suggests that loss of Arctic sea ice could indirectly reduce this trend by modifying the jet stream and mid-latitude weather patterns.8,9
Projections of precipitation changes are less certain than projections of temperature increases.4 Winter and spring precipitation is projected to increase, especially but not exclusively in the northern part of the region (Ch. 2: Our Changing Climate, Key Messages 5 and 6).4,10 A range of model projections for the end of this century under a higher emissions scenario (A2), averaged over the region, suggests about 5% to 20% (25th to 75th percentile of model projections) increases in winter precipitation. Projected changes in summer and fall, and for the entire year, are generally small at the end of the century compared to natural variations (Ch. 2: Our Changing Climate, Key Message 5).4 The frequency of heavy downpours is projected to continue to increase as the century progresses (Ch. 2: Our Changing Climate, Key Message 6). Seasonal drought risk is also projected to increase in summer and fall as higher temperatures lead to greater evaporation and earlier winter and spring snowmelt.11
Global sea levels are projected to rise 1 to 4 feet by 2100 (Ch. 2: Our Changing Climate, Key Message 10),12 depending in large part on the extent to which the Greenland and West Antarctic Ice Sheets experience significant melting. Sea level rise along most of the coastal Northeast is expected to exceed the global average rise due to local land subsidence, with the possibility of even greater regional sea level rise if the Gulf Stream weakens as some models suggest.6,13 Sea level rise of two feet, without any changes in storms, would more than triple the frequency of dangerous coastal flooding throughout most of the Northeast.14,15
Although individual hurricanes cannot be directly attributed to climate change, Hurricanes Irene and Sandy nevertheless provided “teachable moments” by demonstrating the region’s vulnerability to extreme weather events and the potential for adaptation to reduce impacts.
Hurricane Vulnerability
Two recent events contrast existing vulnerability to extreme events: Hurricane Irene, which produced a broad swath of very heavy rain (greater than five inches in total and sometimes two to three inches per hour in some locations) from southern Maryland to northern Vermont from August 27 to 29, 2011; and Hurricane Sandy, which caused massive coastal damage from storm surge and flooding along the Northeast coast from October 28 to 30, 2012.
Rainfall associated with Irene led to hydrological extremes in the region. These heavy rains were part of a broader pattern of wet weather preceding the storm (rainfall totals for August and September exceeded 25 inches across much of the Northeast) that left the region predisposed to extreme flooding from Irene; for example, the Schoharie Creek in New York experienced a 500-year flood.16
In anticipation of Irene, the New York City mass transit system was shut down, and 2.3 million coastal residents in Delaware, New Jersey, and New York faced mandatory evacuations. However, it was the inland impacts, especially in upstate New York and in central and southern Vermont, that were most severe. Ironically, many New York City residents fled to inland locations, which were harder hit. Flash flooding washed out roads and bridges, undermined railroads, brought down trees and power lines, flooded homes and businesses, and damaged floodplain forests. In Vermont, more than 500 miles of roadways and approximately 200 bridges were damaged, with estimated rebuilding costs of $175 to $250 million. Hazardous wastes were released in a number of areas, and 17 municipal wastewater treatment plants were breached by floodwaters. Agricultural losses included damage to barn structures and flooded fields of crops. Many towns and villages were isolated for days due to infrastructure impacts from river flooding (see also Ch. 5: Transportation, “Tropical Storm Irene Devastates Vermont Transportation in August 2011”).17 Affected residents suffered from increased allergen exposure due to mold growth in flooded homes and other structures and were exposed to potentially harmful chemicals and pathogens in their drinking water. In the state of Vermont, cleaning up spills from aboveground hazardous waste tanks cost an estimated $1.75 million. Septic systems were also damaged from high groundwater levels and river or stream erosion, including 17 septic system failures in the state of Vermont.18
Sandy was responsible for about 150 deaths, approximately half of which occurred in the Northeast.19 Damages, concentrated in New Jersey, New York, and Connecticut, were estimated at $60 to $80 billion, making Sandy the second most costly Atlantic Hurricane in history behind Katrina.20 It is also estimated that 650,000 homes were damaged or destroyed, and that 8.5 million people were without power.19 Floodwaters inundated subway tunnels in New York City (see also Ch. 5: Transportation, “Hurricane Sandy”). Sandy also caused significant damage to the electrical grid and overwhelmed sewage treatment plants.19 In New Jersey, repairs to damaged power and gas lines are expected to cost about $1 billion, and repairs to waste, water, and sewer systems are expected to cost $3 billion.
Many of these vulnerabilities to coastal flooding and sea level rise (Ch. 2: Our Changing Climate, Key Message 10) and intensifying storms (Ch. 2: Our Changing Climate, Key Messages 8 and 9) – including the projected frequency of flooding of tunnels and airports – were documented as early as 2001 in a report developed in support of the 2000 National Climate Assessment.21 Despite such reports, the observed vulnerability was a surprise to many coastal residents, which suggests improved communication is needed.
Over the last decade, cities, states, and agencies in the New York metropolitan region took steps to reduce their vulnerability to coastal storms.22,23 In 2008, New York City convened a scientific body of experts – the New York City Panel on Climate Change (NPCC) – and formed a Climate Adaptation Task Force comprised of approximately 40 agencies, private sector companies, and regional groups. A process, approach, and tools for climate change adaptation were developed and documented in New York City11,24 and New York State.25 In 2012, the NPCC and Climate Adaptation Task Force were codified into New York City law, a key step towards institutionalizing climate science, impact, and adaptation assessment into long-term planning.26
These initiatives led to adaptation efforts, including elevating infrastructure, restoring green spaces, and developing evacuation plans that helped reduce damage and save lives during Irene and Sandy (also see discussion of Hurricane Sandy in Ch. 11: Urban). As rebuilding and recovery advances,26 decision-making based on current and projected risks from such events by a full set of stakeholders and participants in the entire Northeast could dramatically improve resilience across the region.