Has Earth’s Temperature Always Fluctuated?
By: Taylor Knoble
Tags: Climate Change, Science, Global Warming, Climate

The arguments of climate-change deniers are many and varied, but one of the refrains that I hear most often is: “The Earth’s temperature has always been in flux because of natural warming and cooling cycles. Therefore, temperature changes are natural and are not caused by human activity.” Like many arguments against anthropogenic (human-caused) climate change, this one is based in truth, but applies that truth incorrectly to yield a falsehood. Here, we will explore the ways in which the Earth’s temperature natural fluctuates, and we will use this knowledge to examine how these natural temperature variations do not contradict the existence of anthropogenic climate change.

Solar Activity Cycles

One of the many ways reasons why the Earth’s temperature fluctuates is the presence of solar activity cycles. The sun’s brightness is not constant, and instead increases and decreases over a period of about 11 years. While the complete mechanism of the solar activity cycle is not entirely understood, scientists know that changes in the amount of material ejected from the sun and changes in the number and size of sunspots can have an effect on the sun’s brightness and can therefore influence the Earth’s temperature.

Photo by Jonathan Borba on Unsplash

However, because this cycle lasts only 11 years, it does not cause any long-term changes in the Earth’s temperature. If the solar cycle were the only factor influencing the Earth’s climate, we would expect the average surface temperature of the Earth to remain the same over long periods, even if there are small, regular fluctuations.

Axis Tilt

Another natural factor that affects the Earth’s temperature is our planet’s axis tilt. You may remember from middle or high school science class that the Earth does not rotate perfectly upright, and that it instead rotates at a 23.5-degree angle. This is why we have seasons in northern and southern latitudes — depending on where the Earth is in its orbit around the sun, different halves of the planet are tilted toward or away from the sun.

However, the Earth’s tilt has not always been 23.5 degrees, and in actuality, it is constantly shifting. Throughout history, the Earth’s tilt has ranged from about 21.5 degrees to 24.5 degrees. When the tilt angle is smaller, seasons are less pronounced and when the angle is larger, seasons are exaggerated. One cycle, in which the tilt angle goes from one extreme to the other and back again, lasts about 40,000 years. Perhaps predictably, the last occurrence of a maximum tilt (featuring extreme seasons) was roughly 10,000 years ago, during our most recent ice age. The Earth is currently moving from this large tilt angle to a lesser tilt, and we would indeed expect this process to warm the Earth by lessening the intensity of winters and melting polar ice. This phenomenon has long been a sticking point for climate change deniers who cite this long-term cycle as the primary cause of Earth’s temperature increase.

Why These Arguments Don’t Stack Up

These are just two of many ways in which the Earth is naturally warming, but ultimately, attributing temperature changes solely to any or all of these natural causes is untenable for one basic reason. What all of these arguments have in common is that they fail to account for the rate at which the Earth’s temperature is increasing. By studying past temperature fluctuations, scientists are able to model the rate at which Earth’s temperature would be increasing if only natural factors were at play. What they have found time and time again is that the actual rate of temperature increase is far greater than can be accounted for by any natural phenomena. Scientists do not analyze global warming by comparing current temperature increases to a flat, unvarying model. Instead, they compare the current rate of warming to a fluctuating background rate. While the Earth has indeed been warmer in the past than it is now, it has never warmed as quickly, and when the Earth warms too quickly, organisms do not have time to adapt.

11 Reconstructions of Temperature Changes. Image by Robert A. Rohde on Wikimedia Commons

The ultimate conclusion? The Earth’s natural temperature fluctuations are very real, but they do not account for the immense rate of temperature increase that we are currently seeing. Anthropogenic climate change is very real, and the presence of natural temperature variation does not refute this fact.

When considering complex scientific issues like climate change, it is crucial to seek information from sources that offer nuanced views. The argument that the Earth is warming naturally is an excellent example of how news sources vastly oversimplify and misrepresent a complex issue for political gain. It is a sneaky argument in that it is based on a true fact; however, this fact is incorrectly applied to reach an incorrect and harmful conclusion. Unfortunately, many climate-change-believing sources also fall victim to the mistake of oversimplification by simply denying that the Earth does, in fact, have natural temperature cycles. This denial only serves to fuel the arguments of climate-change skeptics by giving them their own falsehood to latch onto.

To other writers: We must seek to present climate change in a way that acknowledges its incredible complexity and uses solid science (not oversimplified science) to refute the arguments of climate change deniers.

To readers: We must seek to gather comprehensive information about scientific issues, and we must carefully base the positions we take based only on objective, verifiable, and accurately represented facts.

Ultimately, we must recognize that there are not “two sides” to the climate change debate. When it comes to proven science, there isn’t even a debate to begin with.