I’ve not met a single rational person who denies global warming. The warming trend of the last 150 years or so is universally accepted and documented. However, climate scientists disagree on details, like when the warming began and what caused it.

Contrary to public perception, global warming did not begin with the industrialization of our society, a period during which there was an exponential increase in carbon dioxide (CO2) emissions from anthropogenic sources.

The current warming trend began in the 19th century when the Little Ice Age—which had prevailed for at least two centuries—came to an end. No significant anthropogenic CO2 emissions brought the Little Ice Age to its end. The warming appears to have been purely natural.

And the most likely cause is the sun.

Earth’s temperature levels are regulated primarily by changes in the sun’s activity. The intensity of solar activity influences changes in our climatic system.

Changes in solar activity are usually measured by the number of sunspots. Scientists observe periodic variations in the average number of sunspots and categorize them as “solar cycles.”

Each solar cycle lasts roughly 10 to 11 years and usually correlates closely with temperature on earth.

Weak cycles, with fewer sunspots, usually result in cold climatic conditions on earth.

Such was the case with the Little Ice Age, when solar cycles were weaker than any since then. Climatologists refer to the extremely low periods as the “Maunder Minimum” (~1645-1715) and the “Dalton Minimum” (~1790-1830).

Likewise, strong solar cycles result in warmer temperatures. The relatively rapid warming post-Little Ice Age can be attributed to increased solar activity.

Solar activity in the past 60 years has been higher than average for the 1,150-year period for which we have data. This is the primary reason for the rise in temperatures in the 1970s through 1990s.

Satellite temperature measurements show no significant warming since then. For the past 19 years, temperature levels have remained largely stable. Unsurprisingly, this lack of warming coincides with a decline in solar activity.

Alarm bells went off in recent years when scientists began predicting that we might be headed for a solar minimum. The recent paper on solar cycles 24 and 25 validates their concern and warns that the upcoming solar minimum could be more severe than the brutal Maunder Minimum.

The effects of efforts to reduce CO2 emissions, regardless of whether we succeed, will be minuscule compared with the cooling impact of a solar minimum.

Lawrence Weisdorn

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