Re: “Letter to the editor: Global warming cycles part of normal sequence of events” (Page A6, April 28):

The letter’s author correctly notes that the current El Niño is responsible for a large part of the high temperatures of the last year. Unfortunately, the headline written by the newspaper conveys the impression that there’s nothing else going on.

The El Niño extreme is a bump in a long uphill road that is decidedly not normal. Global surface temperatures have risen 1.6 degrees since the 1951-1980 average because carbon dioxide in the atmosphere has risen from 280 parts per million to 400. This rise is not part of a “normal cycle.”

If humans continue to generate more CO2 than natural sinks can remove, Earth’s average temperature will continue to increase, ice will continue to melt and sea level will continue to rise. This will lead to more extreme weather, more superstorms and increased stress and disease among lobsters, cod and other species critical to Maine’s economy.

Allen E. Armstrong

Portland