Human-Made Aerosol Emissions Change Rainfall Patterns in the Northern Tropics

Aerosols may just be impacting the northern tropics. Scientists have discovered that human-made aerosol emissions from industrial processes have changed the relationship between temperature and precipitation in this region.

In order to better understand how our atmosphere may be affecting the weather, the researchers reconstructed rainfall patterns and temperature over 450 years by analyzing the chemical composition of a stalagmite recovered from a cave in Belize. This stalagmite was formed through deposition of calcium carbonate and other minerals, which precipitated from mineralized water solutions. This water contained oxygen and carbon, which allowed the scientists to analyze signals of climatic and hydrogeological variations.

The researchers discovered out-of-phase relationships between temperature and rainfall within the last 100 years in the northern tropics. This is contrary to how the atmospheric dynamical system is expected to work. In fact, the researchers found that there was a shift in the relationship between temperature and rainfall after the industrial evolution. This hinted that aerosols from industrial emissions have changed these patterns.

"We found an unexpected relationship between temperature and rainfall in the northern tropics with a systemic  trend of decreasing rainfall," said Minghua Zhang, one of the researchers, in a news release. "This corroborated with what the entire research team found over a much longer period of time based on the cave data."

The aerosols reflect the sun's radiation. This, in turn, resulted in the Intertropical Convergence Zone, which is a tropical rainfall belt near the equator, to shift toward the warmer Southern Hemisphere. This, in turn, led to drier conditions in the northern tropics.

The findings reveal how human impacts can drastically impact weather systems and the environment. This is important to take into account when looking at future predictions for rainfall.

The findings are published in the journal Nature Geosciences.

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