Expert Commentary

Trends in daily solar radiation and precipitation coefficients of variation since 1984

2011 study in the online journal of the American Meteorological Society on long-term trends in the variability of sunshine and precipitation.

As anyone who lives on Earth can attest, weather is rarely “average.” However mild or extreme a climate may be, it can be relatively warm one day and cool the next; clouds appear or the sun breaks through; precipitation, if it occurs, tends to do so in bursts. Yet many climate models focus on “average” weather for a particular time and place, something that occurs only rarely in the real world.

This question is important because climate change has the potential to not only increase median temperatures, but also alter weather patterns. Averages and extremes can remain the same even as variability increases — more sunny days, more rainy days — and this can have significant effects on the environment. For example, plants have evolved to expect a certain pattern in weather variability, and a change in that pattern could have serious consequences.

A 2011 study from Princeton University in the online journal of the American Meteorological Society, “Trends in Daily Solar Radiation and Precipitation Coefficients of Variation Since 1984,” looks at the possibility of changes in the variability of daily sunshine and precipitation over time. The study was based on data from NASA’s International Satellite Cloud Climatology Project and the University of Maryland’s Global Precipitation Climatology Project.

Key findings include:

  • Statistically significant changes in solar radiation variability were found across 35% of the planet since 1984.
  • Tropical Africa and Southeast Asia showed large increases in sunshine variability. “These increases in solar radiation variability were correlated with increases in precipitation variability and increases in deep convective cloud amount.”
  • Data indicates that tropical South America has seen correspondingly large changes in solar radiation variability mainly from December through February.
  • Changes in climate variability can have consequences for any process that depends on regular climate variability, including solar energy production and plant photosynthesis. Other impacts could include soil moisture and runoff, carbon sequestration and mosquito populations, which can affect disease outbreaks.

“Given the large number of processes that are nonlinearly sensitive to climate, improving our understanding of current and future high-frequency variability should be a high-priority area of research,” the scholars conclude.

Keywords: global warming, Africa, Asia