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Let’s clear the mystery

In 2021 entitled “The Hot Topic of Temperature Analysis,” I wrote that one of the most common topics people challenge me with is Ice Age cycles. They know that the Earth has experienced several ice ages at fairly regular intervals, and between ice ages were milder periods.

They tell me that what is happening today is just another episode.

In the past month, I’ve had several people who generally tell me that the climate he is periodic or periodic. So when climate scientists talk about sea-level rise trends, for example, they are exaggerating and meaningless. These people suggest that climate scientists have chosen to ignore the cycles.

This is impossible. Courses are all around us. In our daily experiences, one of the most remarkable cycles we experience is the course of the seasons.

It is warmer in summer and cooler in winter. Autumn and spring are transitions between summer and winter. We play and watch different sports in different seasons. We have deeply infused the seasonal cycle into our behaviour.

The seasonal cycle is well understood by the formation of the Earth in relation to the Sun. Because of the Earth’s tilt on its axis of rotation, it’s summer when the northern hemisphere is pointed toward the sun. It is winter when the northern hemisphere is pointed away from the sun. When it’s summer in the northern hemisphere, it’s winter in the southern hemisphere, and vice versa.

Many other examples of cyclical behavior can be explored by looking at the Earth’s seasonal cycle. As we transition from winter to spring to summer, plant growth increases. After the summer plant growth declines and the leaves that grow in the spring months fall to the ground. We also see seasonal cycles in the migration of birds after heat and food.

An intriguing aspect of the transition from winter to summer is that the warmer it gets, the lower the carbon dioxide. This happens because plants require not only heat and water, but carbon dioxide. They consume carbon dioxide so quickly that it reduces the amount in the atmosphere.

diagram showing what

Some of the carbon dioxide is released in the fall; Carbon dioxide increases as the earth cools in the winter. We observe a seasonal cycle due to biological uptake and release of carbon dioxide. Seasonal heating and cooling are dominated by solar energy.

Another reason for the cyclical behavior comes from waves. The common types of waves we see on the surface of lakes and oceans arise from winds pushing the water and accumulating until the force of gravity pulls the water down again.

Water and air are fluids, and fluids are filled with waves. Therefore, we should expect weather and climate to be full of cyclical behavior or period. When all these waves appear together, we are faced with a major complexity.

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I’ve shared these examples as a reminder that we’re so used to cyclical behavior, and the reasons for cyclical behavior don’t have to be ambiguous. Ordinarily, the periodic behavior of waves can be thought of as a balance between two competing forces – the water at the bottom and the wind pressure/gravity above.

An infographic returning carbon dioxide to the atmosphere at the Mauna Loa Observatory in HawaiiWhen we encounter cycle observation, a science-based approach to understanding observation is to ask: What are the competing forces?

Likewise, when we encounter a set of observations full of diversity, we use techniques to explore, identify, and extract waves and periodicity.

This practice is fundamental to climate science and many other types of science and engineering.

When examining a set of observations for evidence of a trend, we must first take into account all other causes of change.

There is, in fact, a common and obvious example of an observational record of a course and a trend together. (See the carbon dioxide log shown in the figure above). These observations from Mauna Loa, Hawaii, show the seasonal cycle described above, which modifies the upward trend of atmospheric carbon dioxide concentrations.

What about courses?

I’ve been asked how we can make sure we’re watching trends in climate rather than the natural cycle. Out of curiosity, there is usually a challenge in asking. This challenge often arises because a large volume of available media is dedicated to maintaining “natural cycles” as an alternative explanation for the trends we observe on Earth. In fact, some advocates of natural cycles are scientists.

I base my answer on several studies designed to describe cyclical behavior in the historical record. The basis for this characterization is an understanding of the competing forces causing cyclical behavior – cause and effect.

Some maintain that the contrast we observe is related to the sun, especially sunspots. There are whole forums where people dedicate Ice Age cycles and the fact that CO2 is known to vary in the absence of emissions from humans burning fossil fuels.

In some cases, those making these arguments claim that mainstream climatologists have ignored these causes of variance. I have never found a case when this is true. In other cases, they tend to attack climate scientists because they have some conspiratorial need to unite the world and deceive them about global warming. This doesn’t make sense to me, but it’s hard to provide a guide for those committed to conspiratorial thinking.

In all cases, those who maintain that cycles are a proxy for trends caused by increased carbon dioxide and methane, choose to take a narrow view of both observations and the ability to describe cyclic behavior and its causes. They hide information. Sometimes, they invoke “nature” as a mysterious force we will never understand.

In the past months, people have told me that they obtained the “data” and analyzed it in person. They find variability, perhaps a cycle, for example, at a time when sea levels have risen over two decades – and then fallen. Thus they conclude that sea level is periodic and there is no trend. They say it is a logical error in a hasty generalization to reach this conclusion. What they can conclude is that there are cycles in sea level observations, and that periodic behavior must be considered in order to draw conclusions about trend. There are legitimate arguments about the methods used to calculate cyclic behavior, but I don’t know of any reliable scientific papers where no such accounting is made.

Ad image: from iStock showing a road collapsing into the sea due to rising sea levels on the coast of Holderness in England.)