Weather phenomenon called WAO to blame

Victoria White (Opinion, May 9) should really do a little background reading in climate science.

If she did she would discover that there exists a phenomenon called the North Atlantic Oscillation (NAO).

The NAO is the dominant mode of winter climate variability in the North Atlantic region, ranging from central North America to Europe and much into Northern Asia. The NAO is a large-scale seesaw in atmospheric mass between the subtropical high and the polar low. The corresponding index varies from year to year, but also exhibits a tendency to remain in one phase for intervals lasting several years.

The NAO cycles between a positive and a negative index over a period of several years. The index is now in its negative phase. The negative NAO index phase shows a weak subtropical high and a weak Icelandic low. The reduced pressure gradient results in fewer and weaker winter storms crossing on a more west-east pathway. They bring moist air into the Mediterranean and cold air to northern Europe.

The US east coast experiences more cold air outbreaks and hence snowy weather conditions. Greenland, however, will have milder winter temperatures.

She would also discover the Atlantic Multidecadal Oscillation (AMO for short). The AMO is an ongoing series of long-duration changes in the sea surface temperature of the North Atlantic Ocean, with cool and warm phases that may last for 20-40 years at a time and a difference of about 1°F between extremes.

The AMO moved into its cold phase at the end of the 20th century. The two phenomena have profound influence on the weather patterns in the Northern Hemisphere, especially in winter and are most likely an important influence on the weather patterns we experienced in recent years.

These changes are natural and have been occurring for at least 10 centuries; they are indeed elements of climatic change but have nothing to do with climate change in the political sense of variations caused by human emissions of CO2, as is clearly implied by Victoria White.

David Whitehead

Glebe

Kinvara

Co Galway