Climate Fact: Earlier “Green-up” Influences Climate
Over the past four decades, there has been a planet-wide lengthening of the “green” period between leaf emergence in the spring and leaf drop in the fall, which is now about 15 days longer than it was in 1970. This lengthening has been linked to the planet’s warming trend. Just as changes in climate can influence plant life, however, changes in plant life can influence climate. For example, as the transition from winter to spring occurs in the Eastern United States, the temperature warms rapidly. Once the leaves emerge, however, the rate of this temperature increase drops. The presence of leaves means that more of the sun’s energy that would be stored as sensible heat (heat you can feel) is instead stored as latent heat in water vapor as soil water flows into the plants and evaporates from the leaves. On the other hand, the lengthening of the “green” period means that the season when plants draw the water from the soil also lengthens, which can cause soil moisture stocks to be depleted earlier in the year. Dry soils in the middle of summer mean less evaporative cooling and higher temperatures. The recent intensification of summer heat waves in Europe has been linked to this phenomenon.
Seasons: Spring, Summer
Source: Peñuelas, J et al. “Phenology Feedbacks on Climate Change.” Science 324 (2009): 887-888.
