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

Climate Change Pressures in the 21st Century

As significant impacts of climate change on natural systems are already evident, it is important to understand how climate change will continue and potentially intensity with time. The USDA Office of Sustainability and Climate has developed an interactive storymap to show what the potential intensification of climate change through this century will look like in the coterminous United States.

The application features three metrics affecting plant growth and survival: growing degree days, plant hardiness zones and heat zones. For each metric, two maps are compared – recent conditions (1980-2009) to possible conditions under a high greenhouse gas emissions scenario (RCP 8.5) at the end of the century (2070-2099). The juxtaposition of the current and projected maps along with the slider between them allows the user to visualize the significant contrast between the present and future potential high emissions scenario.

  • Growing degree days (GDD) are used to describe the season available for plants to grow and mature. Although GDD varies across the US, the projection shows that the growing season will considerably increase everywhere. Some plant species may benefit from a longer growing season, however the model does not include precipitation estimates.
  • Plant Hardiness Zones (PHZs) demonstrate the amount of stress plants can undergo from cold temperatures. Average annual minimum temperatures determine these zones. With winter temperatures rising, a trend expected to continue, plant hardiness zone are shifting.
  • Heat zones map the number of days per year with a maximum temperature of 30 °C (86 °F) or higher. By the end of the century under the high emissions scenario, regions throughout the country will see significant increases in amount of hot days per year.

For each metric, there are links to additional maps, which compare two scenarios of potential climate change (RCPs 4.5 and 8.5) and four different time periods. These potential scenarios demonstrate how climate outcomes can vary depending on human decisions and emissions through this century.

The storymap can be accessed here and the corresponding publication is hosted on the USFS website here