Milankovitch cycles and solar inertial motion are not the 'real reason' behind climate change

Context

In a tweet (archive here) that has been viewed over 1.2 million times, renowned Italian architect and film producer Robin Monotti claims that climate change has "nothing to do with humans." He also suggests that Milankovitch cycles and solar inertial motion are the "real reason" behind the current climate crisis. His tweet reads: "THE REAL REASON FOR CLIMATE CHANGE: The distance of where you are from the Sun is constantly changing because the Earth's orbit around the Sun is VERY irregular… Start by learning the three Milankovitch Cycles, then look into Solar Inertial Motion. None of this has anything to do with humans." 

However, the claims made by Monotti in his tweet are false.

What are Milankovitch Cycles?

According to space agency NASA, around a century ago, Serbian scientist Milutin Milankovitch studied how changes in Earth's position while revolving around the sun alter the former's long-term climate cycles. He identified three types of cycles that affect how much sunlight reaches the Earth and where, thus, influencing how much solar energy or radiation the planet receives. He hypothesized that the "long-term, collective effects of changes in Earth's position relative to the sun," based on the three cycles, "are a strong driver of Earth's long-term climate."

Later named after him, Milankovitch cycles include— the shape of Earth's orbit, called eccentricity; the angle that Earth's axis is tilted with respect to its orbital plane, called its obliquity; and the 'wobble' of the Earth as it rotates around its axis, its precession. 

Do these cycles cause climate change?

NASA debunked the speculation that Milankovitch cycles are the reason behind the current climate change in an article in 2020. Titled "Why Milankovitch (Orbital) Cycles Can't Explain Earth's Current Warming," the article states that the cycles "can't explain all climate change that's occurred over the past 2.5 million years or so." It adds, "And more importantly, they (Milankovitch cycles)cannot account for the current period of rapid warming Earth has experienced since the pre-Industrial period (the period between 1850 and 1900), and particularly since the mid-20th century."

Logically Facts also reached out to experts to understand the effect of these cycles on climate change better. 

Professor Ken Rice, personal chair of Computational Astrophysics at Edinburgh University, told us that these cycles do not change the Earth's average distance from the sun. "So, there is little change in how much energy we receive from the sun," he said. 

"There are times when there is an increase in solar energy being deposited at high Northern latitudes. This can lead to the melting of the ice sheets. This changes the albedo (how much sunlight is reflected), which leads to warming, which can then release carbon dioxide from the oceans, which leads to further warming, etc. This can then move us from a glacial period (with big ice sheets) to an inter-glacial period (what we are in now)," he explained. "However, these processes are slow, and take thousands of years. Current (rate of)warming is much faster than the changes associated with Milankovitch cycles."

He also said, "Given where we are in the current Milankovitch Cycle, we'd expect to be cooling and slowly heading back towards a glacial period, rather than warming above the level of any previous inter-glacial (period). So, our modern warming cannot be due to Milankovitch cycles."

Does solar inertial motion cause climate change?

The combined mass of all the planets and other objects in orbit contributes in determining our solar system's center of mass, known as the barycenter. The sun moves around the barycenter, which, in turn, shifts depending on where the planets are in their orbits. This slight movement of the sun is also called solar inertial motion or SIM.

Any connection between solar inertial motion and the current climate change crisis has been dismissed by experts.

"The suggestion that it (climate change) is due to solar inertial motion is simply, completely wrong. The sun does move around the solar system barycentre, but so does the Earth. The dominant perturber is Jupiter, which is essentially perturbing the sun-Earth system so that both execute a motion around the solar system barycentre. Hence, the average distance from the sun to the Earth does not change due to this motion," Prof Rice told Logically Facts.

"Solar variations can influence the climate, but they tend to be small relative to the impact of human emissions," he added. "However, this motion (solar inertial motion) has no direct impact on our climate."

The human factor in climate change

Dr. Alexa Halford, a scientist at NASA, told Logically Facts, "While the solar cycle (not the Earth's orbit around the Sun) historically does contribute to changes in our climate, and we are still learning more about how many space-driven phenomena may impact climate, it is clear that humans are the primary cause of the current, incredibly fast increases (in climate change) we have seen." 

Experts believe the rapid increase in atmospheric carbon dioxide and other greenhouse gases is a significant driver of the ongoing climate changes experienced today. "I should stress that we are very confident about what is causing the modern warming (i.e., what is causing the climate to change) and it's human emissions of greenhouse gases, predominantly carbon dioxide, into the atmosphere," Prof Rice said.

According to Intergovernmental Panel on Climate Change (IPCC),—a United Nations body that works on climate change— the present warming trend stands apart and results from human activities.  

In a report, IPCC notes that solar irradiance (a measure of radiant energy Earth receives from the sun) cannot explain current global warming. Scientists would anticipate higher temperatures across all atmospheric layers if the warming were primarily caused by a more active sun. However, the observations show a cooling in the upper atmosphere and warming at the surface and lower atmosphere. "That's because greenhouse gases are slowing heat loss from the lower atmosphere," the report states.

NASA also notes, "Scientists are confident Earth's recent warming is primarily due to human activities — specifically, the direct input of carbon dioxide into Earth's atmosphere from burning fossil fuels.

The Verdict

Astrophysicists assert that Milankovitch cycles have not caused the current climate change crisis. It also has nothing to do with the slight movement of the sun or Earth's position relative to the star. The ongoing climate crisis has a proven human factor. Therefore, we mark the claims false.