Recent research has suggested an increasingly important role between the pacific decadal oscillation (PDO) and the El Niño Southern Oscillation (ENSO) on natural phenomena around the globe, including glacial melt variability. These relationships are particularly strong when the PDO and ENSO are in-phase, as they are now.
One study by Bijeesh Kozhikkodan Veettilab, Nilceia Bianchinic, Ulisses Franz Bremerab, Éder Leandro Bayer Maierd, and Jefferson Cardia Simõesa looked at the formation of supraglacial lakes on the Baltoro Glacier in the Pakistani Himalayas from 1978 to 2014. Using a combination of various satellite images the study demonstrated that most of the lakes formed or expanded during the late 1970s to 2008, and that after 2008 the number and size of the lakes decreased.
They discovered that, “the formation and expansion of glacial lakes occurred during the warm regime of PDO, in particular in phase with the ENSO,” and that the shift in 2008 corresponded precisely with the onset of a cool phase of the PDO.
The PDO is primarily a sea surface temperature phenomenon that oscillates in the Pacific Ocean, usually switching from a warm or positive phase to a cool or negative phase every 20-30 years. In the positive phase the Eastern Pacific, along the West coast of the Americas is unusually warm, while the Western Pacific along the East coast of Asia is unusually cool. During the negative phase the opposite occurs.
The PDO is often described as a long lasting ENSO-like event. ENSO is what is commonly referred to as El Niño and La Niña, a sea surface temperature oscillation in the southern Pacific Ocean that is a strong predictor of precipitation anomalies, and therefore drought or flooding, around the globe.
In fact, this summer we are seeing a strong El Niño, also known as a positive ENSO, corresponding with a strong, positive PDO.
Researchers have known or suspected since the early 20th century that El Niño brings strong rains along the United States’ west coast. However, we now know, thanks to the results of the study on the Baltoro Glacier, that the formation and expansion of glacial lakes in the Karakoram Himalayas also occurs during the warm phase of the PDO, in particular when it is in phase with ENSO.
According to The Weather Chanel, “Los Angeles, San Diego and over a dozen other California cities set all-time rainfall records for the month of July.” In fact, a National Weather Service meteorologist described these recent rains as “super historic.”
Researchers are beginning to pay more attention to sea surface temperature in the Pacific Ocean, and around the globe, as we are realizing that they influence everything from strong storms in California to glacial melt in the Himalayas.
The PDO was only relatively recently discovered, found in 1997 due to its influence on Pacific Northwest salmon production. Understanding what scientists call teleconnections between these various natural phenomenon can help us better prepare ourselves for the volatile environment in which we live. Knowing ahead of time that when Southern California will have heavy storms, mountain villages in the Himalayas should be wary of glacial lake flooding, can help save time, money, and lives.