Altered relationship of rain and temperature.

• Position: Industrial Revolution

Man-made aerosol emissions from industrial processes have changed the relationship between temperature and precipitation in the northern tropics, maintains an international team of scientists, including Minghua Zhang, dean and director of Stony Brook (N.Y.) University's School of Marine and Atmospheric Sciences. The findings may help to indicate the shifts in seasonal rainfall in Central America, which is critical for agriculture in the region.

The team reconstructed rainfall patterns and temperature over 450 years by analyzing the chemical composition of a stalagmite recovered from a cave in Belize. Stalagmite in the cave was formed through deposition of calcium carbonate and other minerals, which precipitated from mineralized water solutions that contain oxygen and carbon.

The team used the oxygen and carbon isotopic ratios from each layer of stalagmite deposits to recover the cumulative signals of climatic and hydrogeological variations that include rainfall and temperature. Because of the unique seasonal variation of precipitation in Belize, the researchers were able to date the layers of deposits accurately.

Zhang and graduate student Tingyin Xiao conducted research that found out-of-phase relationships between temperature and rainfall within the last 100 years in the northern tropics that is contrary to how the atmospheric dynamical system is expected to work. The stalagmite analysis indicates a shift in the relationship between temperature and rainfall after the Industrial Revolution. The...