Does the Sun Affect our Weather and Climate?

Inside the Thermosphere Climate Index

January 29, 2019

There have many arguments about whether or not variations in the Sun’s activity affect our weather and climate. The Old Farmer’s Almanac’s long-range forecasts are based predominantly upon solar activity, with their basis being that changes in activity on the Sun do indeed directly cause changes in weather patterns on Earth.

Although our seasonal forecasts have been far more accurate than any others made with a similar time frame, until recently nearly all meteorologists and climatologists have not believed that it was even possible for changes in solar output to affect Earth’s weather, let alone control it to a large extent, as we believe is the case.

The reason for their skepticism has to do with the energy output from the Sun, which is known as the solar constant. Technically, it is not really a constant—it does change significantly over billions of years. It also varies over days and years, but as these variations are a tiny fraction of its value, the scientific consensus has been that any changes in solar energy on a shorter-than-geological-era scale are much too small to have any effect on Earth’s weather.

A defining feature of science that helps to make it so valuable is that as new information comes to light, scientific consensus changes, and what was once believed to be incorrect can become the new truth.


Emerging Evidence

Several years ago, a research paper was published by some Russian meteorologists who believed that they had discovered and defined a mechanism by which tiny changes in solar output could have an effect on Earth’s weather. They postulated that these changes affected the top of Earth’s atmosphere, an area known as the thermosphere, which was thin enough for these small changes to have an effect on it—and that these changes were then enhanced by orders of magnitude as they reflected into the troposphere, the lowest portion of the atmosphere, where our weather occurs.

Recently, others have picked up on this research, and its concepts seem to be moving into the scientific mainstream.

The SABER instrumentation aboard the TIMED satellite launched 17 years ago has provided data on the infrared emissions from carbon dioxide (CO2) and nitric oxide (NO), two substances that play a key role in the energy balance of air in the thermosphere. By measuring the infrared glow of these molecules, SABER can assess the temperature at the very top of the atmosphere.

The Thermosphere Climate Index

Martin Mlynczak, at NASA’s Langley Research Center, has developed something called the Thermosphere Climate Index (TCI), which measures the temperatures at the top of Earth’s atmosphere. Although SABER has been in orbit for only 17 years, Mlynczak and his colleagues recently calculated TCI going all the way back to the 1940s. “SABER taught us to do this by revealing how TCI depends on other variables such as geomagnetic activity and the Sun’s UV output—things that have been measured for decades,” he explained. (See the accompanying graph of TCI data, courtesy of NASA.)

As 2019 begins, the Thermosphere Climate Index is on the verge of setting a Space Age record for cold, which reflects the historic low in solar activity in the current cycle.

So, recent data has proven that temperatures in the uppermost portion of the atmosphere vary substantially, in parallel with solar activity. Recent research proposes a mechanism by which these changes can have a significant effect on weather patterns in the lower atmosphere. While these changes in scientific consensus may not come close to the importance of the refinements of Newtonian mechanics made by Einstein early in the 20th century, they do, at the very least, add scientific credibility to the forecast methodology that we use to make your long-range forecasts here at The Old Farmer’s Almanac.


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About This Blog

Mike Steinberg is Senior Vice President for Special Initiatives at AccuWeather Inc in State College, Pennsylvania. He is also a member of the National Weather Association and the Canadian Meteorological and Oceanographic Society.