Season Creep

Climate change is disrupting the natural cycle of seasons

Climate change forces spring to arrive much earlier, while winters to become shorter and milder. This phenomenon has been documented globally and informally dubbed as “season creep.” Season creep can have harmful impacts on agricultural and economic systems by disrupting migration and growing patterns, which threaten to unravel the natural cycles of ecosystems.

Season creep impacts migratory birds, crop growth, flowers and more

Climate change drives season creep. Natural variability can, at best, explain only one-third of the rate of “creep” in the arrival of spring. In the United States, the crop and vegetation growing season has lengthened by 10 days in the past 30 years. Many migratory bird species show up earlier. For example, northeastern birds that spend winter in the southern United States now return to the Northeast an average of 13 days earlier. Spring snowmelts have shifted so that peak melt flow now arrives 1 – 4 weeks earlier. Flowers are blooming sooner – Washington D.C’s famous cherry blossoms are blooming a week earlier on average. Hardwood forests in the Northern Hemisphere are holding their green leaves for over a week longer than normal.

Season creep is an important example of how small changes can have a big impact

Climate change disrupts the critically important timing of events, such as snowmelt and spring bloom, upon which ecosystems and agricultural industries depend. For example, warmer winters can lead to early bud-burst or bloom of some perennial plants, resulting in frost damage when cold conditions occur in late spring. This was the case with Michigan cherries in 2012 and with the maple syrup production in Vermont in 2012, which requires cold temperatures for strong sap flow and good flavor, and the brevity of recent winters cost producers.

Finally, season creep impacts biodiversity, with cascading effects on agriculture, tourism, hunting and fishing. All species do not respond to the change of seasonal cues in the same way. This can lead to mismatches between the availability of flowers and their pollinators or predators and their prey. For example, the pied flycatcher now migrates at the wrong time relative to its prey and has experienced a 90 percent population decline. In some cases, these disruptions can enable takeover by invasive species, as witnessed at Thoreau’s Walden Pond.

For more information on season creep, including the state of scientific understanding, relevant news and specific impacts, visit Climate Signals.

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