The seasonality of the Northeast is central to the region’s sense of place and is an important driver of rural economies. Less distinct seasons with milder winter and earlier spring conditions (very high confidence) are already altering ecosystems and environments (high confidence) in ways that adversely impact tourism (very high confidence), farming (high confidence), and forestry (medium confidence). The region’s rural industries and livelihoods are at risk from further changes to forests, wildlife, snowpack, and streamflow (likely).

This finding is from chapter 18 of Impacts, Risks, and Adaptation in the United States: The Fourth National Climate Assessment, Volume II.

Process for developing key messages:

It is understood that authors for a regional assessment must have scientific and regional credibility in the topical areas. Each author must also be willing and interested in serving in this capacity. Author selection for the Northeast chapter proceeded as follows:

First, the U.S. Global Change Research Program (USGCRP) released a Call for Public Nominations. Interested scientists were either nominated or self-nominated and their names placed into a database. The concurrent USGCRP Call for Public Nominations also solicited scientists to serve as chapter leads. Both lists were reviewed by the USGCRP with input from the coordinating lead author (CLA) and from the National Climate Assessment (NCA) Steering Committee. All regional chapter lead (CL) authors were selected by the USGCRP at the same time. The CLA and CL then convened to review the author nominations list as a “first cut” in identifying potential chapter authors for this chapter. Using their knowledge of the Northeast’s landscape and challenges, the CLA and CL used the list of national chapter topics that would be most relevant for the region. That topical list was associated with scientific expertise and a subset of the author list.

In the second phase, the CLA and CL used both the list of nominees as well as other scientists from around the region to build an author team that was representative of the Northeast’s geography, institutional affiliation (federal agencies and academic and research institutions), depth of subject matter expertise, and knowledge of selected regional topics. Eleven authors were thus identified by December 2016, and the twelfth author was invited in April 2017 to better represent tribal knowledge in the chapter.

Lastly, the authors were contacted by the CL to determine their level of interest and willingness to serve as experts on the region's topics of water resources, agriculture and natural resources, oceans and marine ecosystems, coastal issues, health, and the built environment and urban issues.

On the due diligence of determining the region’s topical areas of focus

The first two drafts of the Northeast chapter were structured around the themes of water resources, agriculture and natural resources, oceans and marine ecosystems, coastal issues, health, and the built environment and urban issues. During the USGCRP-sponsored Regional Engagement Workshop held in Boston on February 10, 2017, feedback was solicited from approximately 150 online participants (comprising transportation officials, coastal managers, urban planners, city managers, fisheries managers, forest managers, state officials, and others) around the Northeast and other parts of the United States, on both the content of these topical areas and important focal areas for the region. Additional inputs were solicited from other in-person meetings such as the ICNet workshop and American Association of Geographers meetings, both held in April 2017. All feedback was then compiled with the lessons learned from the USGCRP CLA-CL meeting in Washington, DC, also held in April 2017. On April 28, 2017, the author team met in Burlington, Vermont, and reworked the chapter’s structure around the risk-based framing of interest to 1) changing seasonality, 2) coastal/ocean resources, 3) rural communities and livelihoods, 4) urban interconnectedness, and 5) adaptation.

Description of evidence base:

Multiple lines of evidence show that changes in seasonal temperature and precipitation cycles have been observed in the Northeast.56148bf0-62f5-4ec7-8dbc-1e356e40bd42^,4de020df-232e-45f8-8d44-f864565f0b84^,73760c11-7b97-4876-a24f-8fb54b01bca9^,f8ba9ecd-1983-4a78-8fd7-f59e1ab07908^,29eee9a5-5945-4651-b199-764cb2400aed^,55f15317-d7a2-4ae3-99f1-5e77129d2dfe^,ee25e7ff-68f2-4935-81d9-b012b0aa88c5 Projected increases in winter air temperatures under lower and higher scenarios (RCP4.5 and RCP8.5)56148bf0-62f5-4ec7-8dbc-1e356e40bd42^,4de020df-232e-45f8-8d44-f864565f0b84 will result in shorter and milder cold seasons, a longer frost-free season,56148bf0-62f5-4ec7-8dbc-1e356e40bd42 and decreased regional snow cover and earlier snowmelt.25c6b777-dbb6-49a7-8b04-4b509b58966b^,73760c11-7b97-4876-a24f-8fb54b01bca9^,f8ba9ecd-1983-4a78-8fd7-f59e1ab07908^,3c756995-85c6-4709-a271-a22b37d72f8e^,8c1a58d2-fd51-4404-b9cf-354edf9ba859^,de18eab1-afc3-4c2c-bfb9-13f9d377507c Observed seasonal changes to streamflows in response to increased winter precipitation, changes in snow hydrology,f9dc4907-65ae-4582-a285-29b5d4732a9f^,ed73b71b-e2bd-41b4-8cf8-b6f293e951da^,208a7c69-bbda-45e4-bded-c44fd8ad21e5^,75c746be-4e8b-48b8-97f9-4e9d31d5df21 and an earlier but prolonged transition into spring74f1e179-6237-49cd-ae8c-acf2980a5803 are projected to continue.dc7250b8-b20f-4b9f-818e-1729746d08c2

These changes are affecting a number of plant and animal species throughout the region, including earlier bloom times and leaf-out,3307a62c-ed45-4399-bcb9-f77e71b1e626^,68d9349a-ec2f-4a72-b0f7-35ebccf1d0bb^,ee25e7ff-68f2-4935-81d9-b012b0aa88c5 spawning,0ce13198-a924-4762-bd5c-00519d8ae3fc migration,39d1cdc8-6302-4642-a4e3-457ee307946f^,18e57808-1999-4c24-911d-abce180ac68b^,f86791eb-c693-466f-9fb0-ac1db4ea40bc and insect emergence,5d339b6f-883e-4cec-afe2-e75a0f638730 as well as longer growing seasons,2cf345a8-4496-4f48-899f-4cbc020b8039 delayed senescence, and enhanced leaf color change.f947ac52-b0ce-4279-9925-63584393c70b Milder winters will likely contribute to the range expansion of wildlife and insect species,1985bce4-5738-4ba6-ac9a-0d676d2ce4a3 increase the size of certain herbivore populationsc94e7da1-3648-49d7-8dc2-6ca97ec26738 and their exposure to parasitism,440bd774-59c5-420f-9fa3-460ece82c2b4^,2ffa1be3-d6af-4c87-a1c3-553777fb75d0 and increase the vulnerability of an array of plant and animal species to change.0095368f-c79d-47b5-89bd-856b38752d03^,f947ac52-b0ce-4279-9925-63584393c70b^,7da52043-249d-4413-9e1a-40ed0659b2f8

Warmer winters will likely contribute to declining yields for specialty cropsb6e8b67c-7042-4b85-b432-033983875e14 and fewer operational days for logging8a427d3d-8b74-4ed8-8ec0-530b4a2fcdc1 and snow-dependent recreation.bff3f502-9bc7-4d5f-859f-636a30c71624^,abb5bf8c-998f-4fe9-b53e-bc8e5dbc6abe^,80dd6dfe-4dea-4253-a65b-53f620805f9a Excess moisture is the leading cause of crop loss in the Northeast,b6e8b67c-7042-4b85-b432-033983875e14 and the observed increase in precipitation amount, intensity, and persistence is projected to continue under both lower and higher scenarios.56148bf0-62f5-4ec7-8dbc-1e356e40bd42^,4de020df-232e-45f8-8d44-f864565f0b84^,29eee9a5-5945-4651-b199-764cb2400aed^,588d6d3e-8c99-4f9c-971b-fcee898756bd

New information and remaining uncertainties:

Warmer fall temperatures affect senescence, fruit ripening, migration, and hibernation, but are less well studied in the regionf773b2e9-428c-455b-82f9-a4dbf065d44b and must be considered alongside other climatic factors such as drought. Projections for summer rainfall in the Northeast are uncertain,4de020df-232e-45f8-8d44-f864565f0b84 but evaporative demand for surface moisture is expected to increase with projected increases in summer temperatures.56148bf0-62f5-4ec7-8dbc-1e356e40bd42^,4de020df-232e-45f8-8d44-f864565f0b84 Water use is highest during the warm season;d4e6a0d4-8428-40e4-8dd9-34b0276d0d40^,81bd7c9e-d465-4eb4-a0d9-5b3f244c839e how much this will affect water availability for agricultural use depends on the frequency and intensity of drought during the growing season.5e012394-93f7-431c-8e19-1022945a6506

Assessment of confidence based on evidence:

There is high confidence that the combined effects of increasing winter and early-spring temperatures and increasing winter precipitation (very high confidence) are changing aquatic and terrestrial habitats and affecting the species adapted to them. The impact of changing seasonal temperature, moisture conditions, and habitats will vary geographically and impact interactions among species. It is likely that some will not adapt. There is high confidence that over the next century, some species will decline while other species introduced to the region thrive as conditions change. There is high confidence that increased precipitation in early spring will negatively impact farming, but the response of vegetation to future changes in seasonal temperature and moisture conditions depends on plant hardiness for medium confidence in the level of risk to specialty crops and forestry. A reduction in the length of the snow season by mid-century is highly likely under lower and higher scenarios, with very high confidence that the winter recreation industry will be negatively impacted by the end of the century under lower and higher scenarios (RCP4.5 and RCP8.5).