Our planet's orbit may have contributed to ice ages

Last week, I featured the methods used to determine the climate of the Earth’s past. Much of the data that has been collected was from ice core samples, especially ones from Antarctica and Greenland. The longest records are from Antarctica that date back to around 800,000 years. Some of the ice core drilling can reach depths of over two miles. In Greenland, ice cores have climate records dating back about 115,000 years, so the information is not as extensive when compared to Antarctica.

The ice core samples, combined with other indicators, would show long-term cycles of warming and cooling over hundreds of thousands to millions of years. The changes in temperature and the greenhouse gas concentrations in ice cores, ancient marine sediments, lake sediments, cave deposits and other data have helped to support the theory that the Earth’s climate changes from very warm to glacial ice coverage across land areas.

One of the main and most popular theories to demonstrate changes in our planet’s long-term climate is the Milankovitch Cycles. It’s believed that the Earth's orbit patterns play a significant role in influencing the Earth's climate over long periods. These cycles are named after the Serbian astrophysicist Milutin Milankovitch, who theorized how variations in the Earth's orbit and axial tilt affect the distribution and intensity of solar radiation, the rays from the sun, that is received by the Earth, which would ultimately impact long-term climate patterns.

One of these cycles are the changes in the Earth’s orbit around the sun, which is called “eccentricity.” Over a period of 100,000 years, the theory suggests, the planet’s orbit changes from what is now an elliptical one, to more circular. At its closest point, the Earth is approximately 91.4 million miles from the sun. At its farthest location, we’re about 94.5 million miles from the sun, a difference of approximately 3 million miles. Despite the incredible heat in the western U.S. last July, the Earth was at its farthest point from the sun July 5, which is called the “aphelion.” The next time our planet will be the closest to the sun in its orbit will be Jan. 3, 2025, which is called the “perihelion.”

Over the last million years, global glacial expansion and melting, based on the evidence, has occurred approximately every 100,000 years. Based on this theory, when the orbit is more elliptical, there is a greater difference in solar radiation received between the closest approach (perihelion) and the farthest point (aphelion). This variation can enhance or diminish seasonal contrasts. Based on this theory, the Northern Hemisphere may have been farther from the sun, rather than closer, during its winter season thousands of years ago, which could have intensified the cooling.

As I’ve mentioned previously, we have seasons because the Earth is tilted on its axis by approximately 23.5 degrees. At this time of year, the Northern Hemisphere is tilted toward the sun, allowing us to receive more direct solar radiation and hotter weather, despite being farther away from the sun.

The second part of the Milankovitch theory describes this “obliquity” as the angle of the Earth's axial tilt relative to its orbital plane, which likely oscillates between about 22.1 degrees and 24.5 degrees over a cycle of approximately 41,000 years. Changes in our planet’s tilt affect the severity of seasons. A greater tilt would mean more extreme seasons (warmer summers and colder winters), while a smaller tilt results in milder seasons. During periods of ice ages, or at least the beginning of them, cooler summers in the Northern Hemisphere would typically lead to expanding glaciers. Scientists believe that the Earth’s tilt is slowly decreasing. 

The third portion of the theory is the “precession,” or the wobble of the planet’s rotational axis. This can change the timing of the seasons relative to Earth’s position in its orbit approximately every 26,000 years. Precession affects the intensity and distribution of seasons.

The Milankovitch cycles may be more than theoretical. Deep sea sediment cores, as well as ice core data, do indicate periods of major climate change during these cycles. For example, when the Earth was experiencing big ice ages, there were indications of different stages of orbital variation found in the sediment and ice cores.

In terms of our local weather, we finally received some measurable precipitation before July expired. It wasn’t a big amount as only 0.04 inches was reported at Cliff’s station and a puny 0.01 inches at the Spokane International Airport. After the brief cool down, temperatures once again hit or exceeded the 100-degree mark late last week. On Friday, Aug. 2, Coeur d’Alene hit 102 degrees with a sizzling 107 degrees at the Spokane International Airport. That was only two degrees from tying their all-time high of 109 degrees.

The rest of this week is not looking to be as hot with highs mostly in the 80s and 90s across the Inland Northwest. However, the drier-than-normal weather pattern is expected to continue with only a chance of isolated showers or a thunderstorm over the next several weeks. The long-range computer models indicate an increasing chance of rainfall toward the middle to the end of the month.

• • •

Contact Randy Mann at randy@longrangeweather.com.