I write to clarify issues related to changes in the heat content of the Earth’s atmosphere and its relationship to climate change. It has recently been claimed by some that increases in atmospheric carbon dioxide (CO2) during the last 70 years has had no measurable impact on the temperature of the Earth.
Climate change deniers argue that there has been a “pause” in the rate of global warming during the last decade. In fact, some claim that the Earth has actually cooled by a mean of 0.7 degrees Celsius (°C) in recent years. However, numerous studies (e.g., Risbey et al. 2018. A fluctuation in surface temperature in historical context: reassessment and retrospective on the evidence. Environ. Res. Lett., 13: 123008) have disproved this claim. The evidence of a warming trend over the past century is unequivocal. Here are the realities:
Between 1880 (the year that accurate record keeping began) and 1980, the Earth’s atmosphere warmed by an average of 0.07°C every 10 years. However, since 1981, annual mean global temperature has increased by 0.18 °C per decade – more than double that of the previous 100 years in just 40 years! In this context, it is important to note that these decadal trends are occurring against a backdrop of natural temperature variability due to seasonal changes in solar radiation and changes in ocean circulation (e.g., fluctuations between La Niña and El Niño events). Thus, for example, global temperatures in 2021 are running cooler when compared to recent years due to a moderate La Niña event in the tropical Pacific Ocean,
Although the mean annual temperature of the atmospheric has varied from year to year, the amount of CO2 in the atmosphere has increased steadily over the last 60 years with little seasonal or inter-annual variability. There is more CO2 in the atmosphere now than at any time in the last 3 million years. According to the National Oceanic and Atmospheric Administration, the amount of atmospheric CO2 in May 2020 hit an average of about 417 parts per million (ppm). This is the highest monthly average value ever recorded, and is up from 415 ppm in May of 2019. The last time global CO2 levels in the atmosphere exceeded 400 ppm was around four million years ago! The result? Nine of the 10 warmest years since 1880 have occurred since 2005, and the 5 warmest years on record have all occurred since 2015.
Finally, one must distinguish between global warming and climate change. Global warming and climate change are not synonyms. “Climate change” includes global warming, but also refers to a broader range of changes that are occurring globally, e.g. increases in the strength of extreme weather events (tropical storms, droughts, floods); changes in global patterns of precipitation, winds and ocean currents; and melting ice caps and sea level rise. These are all consequences of global warming that will profoundly impact our health and wellbeing in the long term.
Tom Malone, Ph.D. is Professor Emeritus at the University of Maryland Center for Environmental Science
Patrick D. Kelly says
Opinion: According to the National Oceanic and Atmospheric Administration, the amount of atmospheric CO2 in May 2020 hit an average of about 417 parts per million (ppm). This is the highest monthly average value ever recorded, and is up from 415 ppm in May of 2019. The last time global CO2 levels in the atmosphere exceeded 400 ppm was around four million years ago!
That is OPINION…NOT FACT and it is wrong.It is NOT the highest EVER recorded…the Yale source below admits it is LOW in the million-year long history of the Earth. The Yale article states that 500 million years ago the Earth atmosphere was rich with about 7,000 ppm CO2. CO2 is also NOT a pollutant, but a valuable atmospheric component in plant respiration and photosynthesis, stimulating green plant growth, producing oxygen vital for life on Earth. This is a well known fact to every biologist, agricultural biologist, horticuturist/botanist that has used CO2 fertilization to boost greenhouse plant yields, or scientists that have shown global “greening” of the surface due to increased forestation and agriculture yields due to our “low to middling” 400 ppm current atmospheric naturally variable levels.
“In the big picture, 400 ppm is a low-to-middling concentration of CO2 for the planet Earth. Some 500 million years ago, when the number of living things in the oceans exploded and creatures first stepped on land, the ancient atmosphere happened to be rich with about 7,000 ppm of carbon dioxide.Jan 26, 2017”
How the World Passed a Carbon Threshold and Why It Matters
https://e360.yale.edu/features/how-the-world-passed-a-carbon-threshold-400ppm-and-why-it-matters…
Bob Parker says
I thank you for providing the link to the Yale Environment article. It was informative; while it did state that 500 million years ago CO2 levels were indeed much higher, it confirmed that the atmospheric CO2 had been under 400 ppm for the past 300 million years with documented increase since industrialization confirming the statements made by Dr. Malone. Additionally, the rate o increase had accelerated since 1980. Indeed, the Yale article expressed concern (one might say “warned”) if CO2 levels were to increase above 400ppm which they have since publication of the article in 2017. The authors ended with the following paragraph:
“If humanity wishes to preserve a planet similar to that on which civilization developed and to which life on Earth is adapted… CO2 will need to be reduced… to at most 350 ppm,” Columbia University climate guru James Hansen has said. We sailed past that target in about 1990, and it will take a gargantuan effort to turn back the clock.
Michael Davis says
Thank you for writing this. The Star Democrat recently ran a column that denied climate change. The author of the column was a retired chemistry teacher. He admitted he studied chemistry in the late 1950s and early 1960s. Based on this, he claimed that carbon dioxide is increasing in the atmosphere by a minuscule amount. Climate change scientists, he claimed were spreading fear, not facts.
Two days before the Star Democrat published that column, NASA reported that the earth was absorbing almost twice the amount of solar radiation today than it was in 2005. I think I remember that correctly. Most of that radiation is being absorbed by the oceans so land temperatures are rising slower. But that is NOT good news. A disaster is here in spite of what is published in our local newspaper.
Thanks for helping to set the record straight.
Max Gresham says
Co2 levels have been higher in the past and the world did just fine, no one agues this point. The question is whether higher co2 levels lead to higher temps or it’s the opposite. I would submit to anyone willing to take their co2 colored glasses the answer is clear. The geologic history is clear on this. 55 million years ago the world warmed suddenly, much higher co2 levels were recorded, but were they the result methane breakdown, common sense says yes. As the earth cooled rapidly after the peak, co2 levels stayed elevated, doing nothing to slow decreasing temps, proving that co2 at the low percentage in our atmosphere do little to affect temps. Methane is most likely a stronger driver. Let’s think more recently. Last ice age ended about 12 k years ago and temps peaked about 5 k years ago with temps much higher than today. Nobody argues these facts. It has been cooling ever since in approximately 500year cycles swings from warmth to cool and back again. The last cycle of cool was the deepest and longest since the last great ice age. Again nobody argues these facts. That cycle ended in the early 1800s, let’s say the last time the Thames consistently froze over, right on schedule. Also 100yrs before any significant man made co2 increase. This warming period, 200 yrs in has yet to surpass the last one 1000yrs ago. You only need to see the Viking artifacts under the Norwegian glaciers to see that. All the man made co2 hasn’t done anything to change that. These are not computer generated ideas, but simple facts you can see with your own eyes.