SAN FRANCISCO, CA., DEC. 11, 2013 — Assessing how climate change will continue to impact the United States will require cataloguing and tracking several indicators of change. At the AGU meeting on Wednesday, Julio Betancourt from the U.S. Geological Survey offered a quick review of some of the indicators of change that future government assessments are expected to include.

Among them is the timing of spring snow melt, an important indicator of warming temperatures that are resulting in shorter winters and earlier onsets of spring. This has been documented in detail in the West, where work for decades has tracked the timing of snow melt in the Sierra Nevada and elsewhere.

The changing timing of snow melt falls into a category of indicators called hydrology, and other indicators in this group include the timing of peak stream flows (a proxy for the timing of peak snow melt), and the timing of freeze/thaw cycles.

Some other categories that follow seasonal changes include:

Phenology: the timing of leafing, flowering, animal migrations, and when animals emerge from hibernation.

Surface climate: direct measurements of temperature, precipitation (rain and snow), the timing of the first and last freeze, etc.

Near-surface dynamics: sea level pressure, wind fields, etc.

Upper level dynamics: El Niño Southern Oscillation, North Atlantic Oscillation, Pacific North American Pattern, etc.

Betancourt spoke of many more specific indicators that scientists are discussing as important for assessing climate change. The onset of spring, for example, has been measured by tracking lilac and honeysuckle blooms, the blooming of Anjou pears in Oregon, the duration of fire seasons and the shifting of specific bird wintering ranges in North America.

More research is needed to reach consensus on the value of specific indicators, and work is ongoing, Betancourt said.