A new study out of the Mexican Institute of Water Technology argues that oscillations in the amount of sunlight reaching the Earth could have a much bigger cooling impact on the climate than previous estimates by climate scientists.

Study author Jorge Sanchez-Sesma examined solar cycle data going back 100,000 years and compared them to about 25,000 years of surface air temperature data in the Congo River Basin. Sanchez-Sesma found that “information from reconstructions and models indicates a potential continental tropical temperature cooling of around 0.5oC for the rest of the 21st century”.

Furthermore, the study argues that varying levels of solar activity explain “most of the variation” in the Congo River Basin’s air temperatures “during the past centuries” — this is important since the river basin is far from the influence of ocean temperatures.

“Our model provides an estimation of a cooling for the 21st century of about 0.5oC, followed by a slow warming trend with small oscillations during more than 4 centuries,” Sanchez-Sesma writes in his study.

Increasingly, scientists have been looking into the climate implications of short and long-term solar cycles. It’s only been in the last 15 years or so that scientists have discovered 6,000-year and 2,400-year solar oscillations. Now, amid reports of the sun “going blank,” scientists are predicting solar activity similar to levels seen during the “Little Ice Age” from the late Middle Ages to the mid-19th Century.

“Not since cycle 14 peaked in February 1906 has there been a solar cycle with fewer sunspots. We are currently more than six years into Solar Cycle 24 and the current nearly blank sun may signal the end of the solar maximum phase,” according to experts at Vencore Weather.

“Going back to 1755, there have been only a few solar cycles in the previous 23 that have had a lower number of sunspots during its maximum phase,” according to Vencore.

Earlier this year, UK Met Office scientists published a study arguing that decreasing solar activity would have a 0.1 degree Celsius cooling effect on global temperatures, with more cooling being felt in North America and Europe. Sanchez-Sesma’s finding of a 0.5 degree Celsius cooling trend of  continental tropical temperatures could imply more overall global cooling from severely reduced solar activity.

Both Sanchez-Sesma’s study and Met Office researchers noted, however, that any predicted cooling from solar activity needs to be considered against other climate forcings, like man-made greenhouse gas emissions. Met Office scientists argue that any cooling impacts from the sun will likely be overshadowed by man-made global warming.

“This research shows that the regional impacts of a grand solar minimum are likely to be larger than the global effect, but it’s still nowhere near big enough to override the expected global warming trend due to man-made change,” Met Office scientist Sarah Ineson said.

“This means that even if we were to see a return to levels of solar activity not seen since the Maunder Minimum, our winters would likely still be getting milder overall,” she added.

Inseon and her team, however, aren’t the first to predict cooling from a solar minimum. Earlier this year, Shrinivas Aundhkar, director of India’s Mahatma Gandhi Mission at the Centre for Astronomy and Space Technology, argued a “mini ice age-like situation” is around the corner.

“The sun undergoes two cycles that are described as maximum and minimum,” Aundhkar said. “The activity alternates every 11 years, and the period is termed as one solar cycle. At present, the sun is undergoing the minimum phase, reducing global temperatures.”

Interestingly enough, scientists at the University of Southampton also predicted a cooling trend in the coming decades, but this cooling will come from natural cycles in the Atlantic Ocean and not the sun.

“The observations of [AMO] from [sensor arrays], over the past ten years, show that it is declining,” Dr. David Smeed, the study’s co-author, said in a statement. “As a result, we expect the AMO is moving to a negative phase, which will result in cooler surface waters. This is consistent with observations of temperature in the North Atlantic.”

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