The Alaskan volcano Mount Redoubt, located 110 miles southwest of Anchorage, has spewed ash into the Earth's atmosphere since March 15. Though it’s 3,000 miles away, experts predict crops in the Midwest may suffer from adverse growing conditions if Redoubt's explosions continue and intensify.

Research shows volcanic eruptions contribute to the formation of either a positive or negative phase of what is known as the North Atlantic Oscillation (NAO), which deals with strength and location of a high and low pressure system in the North Atlantic Ocean. Eruptions in the tropics contribute to the formation of a positive NAO, which typically brings a westerly flow to the U.S. in the wintertime, leading to milder Pacific air over the country.

Conversely, high-latitude volcanic eruptions, such as Redoubt, have been linked to the formation of a negative NAO. This phase can bring cooler-than-normal air across the United States in the winter months. Therefore, below normal temperatures may be featured throughout the year following a high-latitude eruption.

An example of the positive NAO phenomenon occurred back in June of 1991, when Mount Pinatubo erupted in the Philippines and ejected nearly 20 million tons of sulfur dioxide into the stratosphere. The following year, the average global air temperature dropped almost 1.5ºF. This cooling was likely driven by Pinatubo's sulfur dioxide plume that caused a several percentage increase in sunlight reflected by the Earth's atmosphere back into space.

While global average temperature did drop following the Pinatubo eruption, the cold temperature anomalies in the U.S. were most profoundly observed during the subsequent summers. For instance, August 1992 averaged 5ºF to 7ºF below normal in the Iowa. Prior to Pinatubo (going back to 1951), the average August temperature in Des Moines was around 75ºF. In 1992, the average fell to around 67ºF.

Flooding and soggy fields further complicated the growing situation at that time as the wet fields forced late planting. Following the Pinatubo blast, an early season frost affected the Upper Midwest bringing temperatures in the upper 20s into northern Iowa and southern Minnesota. Soybeans there, still maturing due to delayed sowing, were blanketed by frost. Unfortunately, this led to yield reductions as the crop was planted late.

What differentiates Pinatubo from the current Mount Redoubt eruption is both location and magnitude of the eruption. The amount of sulfur dioxide emitted from Redoubt into the atmosphere has yet to be determined. And, the magnitude of the Redoubt eruptions may not be as intense as some prior blasts. However, with the creation of a negative NAO, Redoubt could still bring cooler air to the Midwest.

StormX Senior Meteorologist Richard James examined the historical records from 103 stations in the Corn Belt in the year after the 1991 Pinatubo eruption. James states that these differences may be representative of what can be expected if the Redoubt activity persists and becomes stronger in the months ahead.

He explains, "The first frost (minimum temperature less than 32ºF) in the fall of 1991 was, on average, 10 days earlier than normal across these stations. In the subsequent spring, the last frost was five days later than normal on average at these stations."

The potential for a relatively cold summer or fall 2009 or 2010 have Midwest farmers concerned. Currently, with many fields in the Corn Belt extremely wet from heavy rains in the winter and early spring, planting delays are likely – as they were back in the 1991-1992 season. Therefore, an early frost may spell tough times for late-maturing corn and soybeans.
-- FMI/Nielsen/Lempert E-Newsletter