Ask an in-the-know climatologist, meteorologist or scientist about Earth’s climate history, the time-period in question being between today and 10,000 years back, this followed by the section of world climate history covering the period between the latter and 110,000 years, the two then compared, well, the response you get may surprise you. The short answer: General stability versus general instability, respectively. No one can say definitively why it’s this way. What is, however, definitive is that during the period of relative climate calm, civilization not only took root, but it flourished: 7.5 billion people now inhabit the earth; a number deemed improbable if not impossible to reach in a climate that varies wildly. Think wild temperature swings.
I live in Fresno in California’s San Joaquin Valley. Some recent research I’ve done entails uncovering what Fresno County’s annual average temperature in Fahrenheit is: In this case it’s 64.25 degrees. Monthly average temperatures, meanwhile, range in degrees Fahrenheit from a low of 46 to a high of 83. I might add that along with average global temperature rise (rising about 1.1 degrees Celsius or 1.9 degrees Fahrenheit) since around the year 1800, logic would have it the Valley’s mean temperature plot is as well in that same span of time tracking similarly.
It should be noted that temperature variability occurs regardless of whether climate is stable or it isn’t. What’s also important is to recognize the earth’s average surface temperature, as far as I know, in the past has not seen this kind of meteoric rise in as short a stretch as what is being encountered in current times.
Moving on, there is fierce debate at times over what’s behind this latest exponential average global temperature-at-the-surface climb. While I can’t confirm positively that average yearly Valley temperatures have ranged upward between when I first moved to Fresno in 1977 and today, what I can tell you unequivocally is that there has been a disruption in climate in the Valley starting, according to what I understand, circa 1935 and lasting into the ‘70s, with a second climate-disruption wave beginning in the 1980s and carrying through to the present.
According to related research findings: Prior to the 1930s, cold-weather fog, also known as tule fog, was not a widespread problem. Then over time between 1935 and the 1970s, tule fog in the cold-weather months in the Valley grew much more extensive, that is, until a reversal, commencing in the 1980s and extending to today, took hold. At the root of this shift, as I understand it, is a change in concentration over time of airborne ammonium nitrate molecules. (See: “Falling levels of air pollution drive decline in California’s tule fog,” Apr. 20, 2019 Air Quality Matters post to get a more in-depth perspective).
So here is a case where air pollution and a decrease thereof have apparently caused corresponding proportional disruptions to area climate.
“[O]n June 15, 1991, Mount Pinatubo on Luzon, a main island in the Philippines erupted, hurtling roughly 17 million tons of sulfur dioxide … into the stratosphere. One event leading to another, what transpired next was, in fact, the formation of clouds of sulfate aerosols. As it turned out, the cover from the clouds was indeed widespread. And, because of such, large swaths of the planet’s surface in 1992-‘93 underwent solar radiation loss and that, in turn, translated to a GMST loss of perhaps 0.4 degrees Celsius. Meanwhile, the Earth’s surface over the Northern Hemisphere had cooled by upwards of 0.5 to 0.6 degrees Celsius,” as I had written in the Jul. 27, 2020 Air Quality Matters “1940s-‘80s global-mean-surface-temp normalization: Were Earth-covering sulfate aerosol clouds the cause?” post.
What this shows is the inversely proportional relationship between volcanically sourced sulfur dioxide (in this case via Mount Pinatubo’s 1991 eruption) thrust into the stratosphere and the consequent resulting alluded-to drop in surface temperature experienced here on Earth. From this, by extension, it seems logical that geo-engineering along these lines could hold promise in the context of humans trying to regulate GMST through, you guessed it, unnatural or unorthodox actions, processes, practices.
Back to the stable-climate issue
So, what is different this time around over this 10,000-or-so-year span to cause this latest period of relative climate stability?
One possible explanation is that with civilization having firmly taken root during this period and with growth of civilization facilitated through certain established population perpetuation and expansion practices undertaken (such as the practices of agriculture, cooking, home heating and lighting to name four) involving land and tree clearing and preparation, community and later city building and expansion, important resources exploitation necessary to advance length and quality of life and that of life itself (societal improvement, in other words) as well as developing the means with which to do this via mechanization, automation, industrialization, what-have-you, has come a strong reliance on fossil fuels and the burning thereof, that which has allowed for the generation of energy, energy that has been harnessed and put to use, and it is through this arrangement that has, over time, seen the very same processes that have resulted in the production of more and more air-pollutant and climate-warming emissions to not only alter the makeup of air but to drive the atmospheric warming of it as well. Again, this is but one possibility, though it is not the only one.
It’s fact that the planet has gone through alternating times of warming and cooling, and all repeating with relatively consistent regularity. That’s the information that historical evidential records have given us. There is every reason to expect this seemingly perpetual hot/cold alternation will continue.
What’s puzzling, on the other hand, is why the presence of the 10,000-or-so-year-long stretch of relative climate calm that we are in the midst of at present? That’s the $64 million question.
– Alan Kandel
This post was last updated on Sept. 11, 2022 at 11:11 p.m. Pacific Daylight Time.