Numerous letters on “global climate change,” such as those by Mr. Wiese, Mr. Rogers (July 7), Mr Siewell, and Mr. Brennan (July 21), and opinion pieces in various newspapers in Oregon and elsewhere either say: “Climate change is a big hoax!” or “Climate change is already happening.”  As “proof” for their respective position, the opposite sides point to recent events, such as warmer (or colder) winters somewhere, colder (or warmer) summers somewhere else, colder/warmer Antarctic temperatures, little change in average global temperature for more than a decade, etc.  Recent events, however, prove nothing about climate change, because changes in climate occur over a much longer time frame than seasonal or yearly events.

As a scientist (but not a climate scientist) and an engineer, I have followed the “climate change” debate as an impartial observer for the United States Air Force and several non-partisan/non-political non-profit organizations for more than 35 years, first when it was generally called “global cooling" (or “nuclear winter,") then “global warming," and now “global climate change." [Note: I am not now and never have been a "climate scientist," nor have I ever been involved directly in any "climate" research.]

For the first 20 of the past 35-plus years, I followed the science professionally as a neutral, disinterested observer, after that, as an interested citizen. My involvement began when, in my capacity as an Air Force Reserve scientist, an Air Force research laboratory asked some military and civilian scientists to review "global cooling" — the "nuclear winter" scenario — then both "global cooling" and "global warming," and finally “global climate change." We wrote summaries and reports, and advised interested government personnel. I continued to follow "climate change" as an interested citizen after retiring from the Air Force Reserve. Professor Paul Crutzen, whom I met and interviewed about 1981, was an early researcher into "global cooling," and later a Nobel prize winner in chemistry for his research on ozone depletion in the upper atmosphere, resulting in the ozone hole phenomenon over the Antarctic.

First, let's define the term “climate.” An online dictionary defines "climate" as "the composite or generally prevailing weather conditions ... over a series of years." Another dictionary defines "climate" as the "average course or condition of the weather ... over a period of years...."  I expect other definitions of "climate" also include "average," "weather," and "period of years.” One professor succinctly defined "climate" as "the statistics of weather." In the definition of "climate," the "period of years" is normally considered to be at least 30 years, and often hundreds or thousands of years.

Because "climate" refers to long-term average weather conditions, "climate change" must also refer to long-term changes in those average weather conditions. Thus, if someone says, for example, that Oregon is experiencing "climate change," because this past winter was mild, that isn't "climate change." The "Dust Bowl" drought years in the 1920s and 1930s wasn't "climate change" either. Neither is it "climate change" when there is a drought for five years (California, southeast Oregon recently) or seven years (Egypt/Near East in the Bible). Nor was it "climate change" when someone said a few years ago that there was no "climate change" because the global mean temperature leveled off for a dozen years. All those time periods were too short to qualify as "climate change."

Unfortunately, when discussing "climate," scientists have difficulty determining averages for many "weather" conditions, because humans have only been systematically observing and recording "weather" data for about 150 years. In addition, most weather data is recorded in populated areas on land, with little data available over oceans and sparsely inhabited land until satellites started systematic remote measurements about 50 years ago. Thus, what "global" data scientists have available to them for study is less extensive and possibly less representative of the actual "global" weather and climate than any of us would like.

Now, with those caveats in mind, "GISTEMP Global Temperature 1880 – 2016" [a web site for lots of graphs and data is https://data.giss.nasa.gov/] shows the "best" data available for global surface temperature change since 1880, the difference between yearly "global average temperature" and the 1950 – 1980 "average."  The graph shows that global temperature decreased for about 30 years (1880 – 1910), rose for about 30 years (1910 – 1940), dropped for a few years during World War II, then leveled off for about 30 years (1945 – 1975), rose again for about 25 years (1975 – 2000), remained fairly level for about a dozen years (2001 – 2013)—but at a temperature significantly higher than the period from 1880 – 1920—then has risen rapidly for the last three years. [Note that the past three years (2014, 2015, and 2016) have been the three warmest years on earth since 1880, and that the 18 warmest years since 1880 have all occurred in just the past 20 years.] Although there have been several centuries-long increases and decreases in the global average temperature since the last ice age, there does not appear to be any previous change that compares to the rate of increase observed over the past century.

Since the average global temperature during the time when it more-or-less leveled off (2001 – 2013) was about 0.9 Kelvin/Celsius degree (or about 1.6 Fahrenheit degrees) higher than the average between 1880 and 1920, this lent some credence to the claim by some observers between 2010 and 2013 that global warming might have slowed down or ceased during the first dozen years of the 21st century. However, the rapid rise over the past three years makes us wonder what the next few years have in store. Remember, though, that "climate" is a long-term average, and these past few years do not necessarily indicate “global warming" (or “global climate change") is here to stay.

In summary, as a neutral observer, although the global temperature has increased by a statistically significant amount over the past century, I do not think we yet know for certain whether or not we are in a permanent period of global warming. Based on the significant temperature change since the years 1880 – 1920, I believe we are seeing both regional and global climatic changes, but I do not think we yet know for certain what will happen in the future.

[If you are interested, I invite you to search the Internet.  Hundreds of articles and graphs indicate that other "weather" data (e.g. precipitation, amount of sunshine, snow/ice cover, and others) have changed over the years, centuries, or longer time periods.  Some appear to show that the global climate is warmer now than any time since the most recent Ice Age, and that it continues to get warmer; others appear to indicate the opposite.]

The writer, a retired U.S. Air Force Colonel, lives in unincorporated Clackamas County.