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Shifts in Growing Degree Days, Plant Hardiness Zones and Heat Zones

Growing Season Length Warmer temperatures have resulted in a longer freeze-free season and longer growing season across the region (Frumhoff et al. 2007, Kunkel et al. 2013). The freeze-free season, which is the period between the last occurrence of 32 °F in the spring and the first occurrence in the fall, was about 10 days longer in the Northeast during 1991 to 2010 compared to 1961 to 1990 (Kunkel et al. 2013). An examination of the end of season for forests (based on leaf senescence) from 1989 to 2008 found that the end of season is occurring later in the fall and that for much of the region, the delay in end of season is related to the number of cold-degree days (Dragoni and Rahman 2012). Increases in the growing season length and other climatic factors have caused noticeable changes in the timing of biological activities in the Northeast as well as across the world (Ellwood et al. 2013, Schwartz et al. 2006, Walther et al. 2002).

Climate change is already having substantial effects on natural systems and the benefits they provide. Forest vegetation may face increased risk of moisture deficit and drought as climate change lengthens the growing season. Therefore, it is important to understand and consider how climate change may intensify through this century in order to prepare for future changes. A tool to help assess potential climate change pressures was developed by the US Forest Service Northern Research Station. The tool displays a series of maps to better represent potential variability of projected climate change across three 30-year periods for the conterminous United States. 

This application features three metrics that influence plant growth and survival:

  • Growing Degree Days
  • Plant Hardiness Zones
  • Heat Zones

Each pair of maps presented in the tool compares recent conditions (1980-2009) to potential conditions under a scenario of high greenhouse gas emissions at the end of the century (RCP 8.5; high level of emissions over the next several decades). The tool provides a visual contrast between two scenarios of potential change (RCPs 4.5 and 8.5), and four different time periods. These scenarios emphasize the variation of possible climate outcomes as a result of human decisions driving emission trajectories through this century.

Check out the interactive story map tool to visualize potential changing pressures relevant to your area.



The storymap was created by Stephen Matthews, Louis Iverson, Matthew Peters, and Anantha Prasad, USDA FS OSC, USDA Northern Forests Climate Hub, and Northern Institute of Applied Climate Science

Please cite this story map as: USDA Office of Sustainability and Climate (2018). Climate Change Pressures in the 21st Century. Retrieved from

More information on the methods used to develop these maps is available in the report Assessing potential climate change pressures across the conterminous United States: mapping plant hardiness zones, heat zones, growing degree days, and cumulative drought severity throughout this century by Stephen Matthews, Louis Iverson, Matthew Peters, and Anantha Prasad. This dataset is also available for download on the Research Data Archive.


Text on this page was drawn from: Janowiak et al, 2018. New England and northern New York forest ecosystem vulnerability assessment and synthesis: a report from the New England Climate Change Response Framework project. Gen. Tech. Rep. NRS-173. Newtown Square, PA: U.S. Department of Agriculture, Forest Service, Northern Research Station. 234 p.

Other references - 

  • Dragoni, D.; Rahman, A.F. 2012. Trends in fall phenology across the deciduous forests of the eastern USA. Agricultural and Forest Meteorology. 157: 96-105.
  • Ellwood, E.R.; Temple, S.A.; Primack, R.B.; Bradley, N.L.; Davis, C.C. 2013. Recordbreaking early flowering in the eastern United States. PLoS ONE. 8(1): e53788.
  • Frumhoff, P.C.; McCarthy, J.J.; Melillo, J.M.; Moser, S.C.; Wuebbles, D.J. 2007. Confronting climate change in the U.S. Northeast: science, impacts, and solutions. Synthesis report of the Northeast Climate Impacts Assessment (NECIA). Cambridge, MA: Union of Concerned Scientists. 160 p. Available at http://www. (accessed April 28, 2014).
  • Kunkel, K.E.; Stevens, L.E.; Stevens, S.E.; Sun, L.; Janssen, E.; Wuebbles, D.; Rennells, J.; DaGaetano, A.; Dobson, J.G. 2013. Regional climate trends and scenarios for the U.S. National Climate Assessment. Part 1. Climate of the northeast U.S. NOAA Technical Report NESDIS 142-1. Washington, DC: U.S. Department of Commerce, National Oceanic and Atmospheric Administration. 79 p. Available at NOAA_NESDIS_Tech_Report_142-1-Climate_ of_the_Northeast_U.S.pdf (accessed April 30, 2014).
  • Schwartz, M.D.; Ahas, R.; Aasa, A. 2006. Onset of spring starting earlier across the Northern Hemisphere. Global Change Biology. 12(2): 343-351. 2486.2005.01097.x.
  • Walther, G.R.; Post, E.; Convey, P.; Menzel, A.; Parmesan, C.; Beebee, T.J.C.; Fromentin, J.M.; Hoegh-Guldberg, O.; Bairlein, F. 2002. Ecological responses to recent climate change. Nature. 416(6879): 389-395.