Milankovitch cycles

Without the Burning of Fossil Fuels Earth would be cooling

Superfact 140: Naturally occurring climate change caused by Earth’s orbital cycles (Milankovitch cycles) would currently result in a slight long-term cooling trend. Other natural causes of climate change such as solar activity, volcanic trends, and other sources of carbon emissions do not increase Earth’s average global temperature. In addition, reductions in Ozone depleting gases have a cooling effect. Our fossil fuel emissions are the cause for the current sharp increase global temperature as well as for it not getting colder.

The graph shows the temperature since the last ice age. There is a maximum temperature about 6,000 years ago, then a cooling and then a sharp uptick in temperature. | Without the Burning of Fossil Fuels Earth would be cooling — Global temperature from 20,000 BCE until now. Notice the Holocene Thermal Maximum around 6,000 years ago and the relatively stable temperature during the last 10,000 years, coinciding with the development of human civilization. Pay special attention to the sudden sharp increase in average global temperature at the end.

The sharp spike in global average temperatures towards the right side of the graph above is caused by us humans, chiefly by our burning of fossil fuels. However, the rest of the graph corresponds to natural causes of climate change. The wild swings in the average global temperature during the ice ages are chiefly caused by Earth’s orbital cycles, the so called Milankovitch cycles. <<Link-1>> There are three main Milankovitch cycles:

Changes in Earth’s orbital eccentricity, with 100,000 year cycles.
Changes in obliquity or axial tilt, with a 41,000 year cycle.
Axial precession or wobble, with a 26,000 year cycle.

Three illustrated orbital cycles. On the left orbital eccentricity, in the middle is the axial tilt and on the right axial precession. — Illustration of Milankovitch cycles from MIT’s Climate Primer.

The Milankovitch cycles cool Earth, and the sun, climate oscillations and ocean currents, volcanoes and emissions part of the carbon cycle do not cause any significant global warming in the long run. In addition, reductions in Ozone depleting gases have a cooling effect and so does our emissions of aerosols. In other words, if it weren’t for our carbon emissions Earth would be getting colder. I believe this is a surprising and important fact and therefore a super fact.

Several scientists, astronomers and organizations around the world keep track of the orbital cycles including NASA, NOAA, etc. The Milankovitch cycles explain the ice ages, but these cycles are too long to explain the recent one or two century spike in average global temperatures. Furthermore, the Milankovitch cycles would currently slowly cool the atmosphere not warming it.

The graph shows wild swings over the last 150,000 years and then a very sharp uptick at the end. | Without the Burning of Fossil Fuels Earth would be cooling — Temperature record for the last 150,000 years. Orbital cycles are the main cause for these swings but not the temperature spike at the end. This picture is taken from this article.

In addition, different causes for climate change leave behind different fingerprints in how the heat is distributed across time, seasons, atmospheric layers, and geography. The “fingerprint” of the current warming is that of greenhouse gases being the cause for it and not orbital cycles. For example, the upper atmosphere is cooling an effect caused by the “blanket effect” caused by greenhouse gases. You can read more about how the current rapid global warming is different from past ice age temperature swings here.

To read more about the Milankovitch cycles click here.

The Sun Does Not Contribute to Global Warming

The sun cannot explain the average increase in global warming either. According to data from NASA, solar energy output has shown no net increase since the late 1970s, in fact it is at its lowest in over a hundred years, and again the sun has the wrong “fingerprint”. You can read more about this here.

A thin yellow line graph (on black background) shows the sun’s irradiance fluctuating every 11 year. However, it does not go up overall, but it rather goes down even though the red line graph showing temperature rises sharply. — Solar irradiance (yellow) plotted with temperature (red) since 1880. NASA, Public domain, via Wikimedia Commons.

Volcanoes and Other Natural Sources of Carbon Emissions Do Not Contribute to Global Warming

Human emissions are roughly 60 to 100 times greater than all global volcanic output combined. In addition, volcanoes are part of the carbon cycle which has been stable for a long time. Thus, volcanoes are not the cause of the current rapid global warming. You can read more about this here.

The graph shows human emissions exceeding that of volcanoes around 1870 and then rising rapidly. | Without the Burning of Fossil Fuels Earth would be cooling — Human carbon missions (green line) vs. emissions from volcanic eruptions (purple line at bottom). Data from the Carbon Dioxide Information Analysis Center (CDIAC) at the DOE’s Oak Ridge National Laboratory and Burton et al., 2013.

There are a lot of natural carbon emissions from the soil, rotting plants, animal and human respiration, and oceans, and a small amount from volcanoes. However, carbon is also absorbed by the oceans, and by plants via photosynthesis, etc., and this creates a balance that has existed for many thousands of years. This is called the carbon cycle. Even though the carbon emissions from burning fossil fuels are smaller than some of the naturally occurring carbon emissions, it is the carbon emissions from burning fossil fuels that are behind the increase of carbon in the atmosphere because they are a new addition that disrupts the carbon cycle.

The carbon cycle in the picture shows that the terrestrial biosphere is absorbing 120 Gigatons of carbon from the atmosphere and emits 60 Gigatons to the atmosphere. It also adds 60 Gigatons of carbon to terrestrial soils. It also shows the Surface of the Ocean both emitting and absorbing 90 Gigatons of carbon to the atmosphere and both emitting and absorbing 90 Gigatons of carbon to the deep ocean. There are additional flows in the picture. It is complex but stable cycle. — The picture above was drawn by me and is an adaptation of Figure 3.1 on page 31 in the book “The Physics of Climate Change by Lawrence M. Krauss”.

Conclusion

Orbital cycles, so called Milankovitch cycles, changes climate naturally but they are in a cooling phase. The sun is cooling a bit. Reductions in Ozone depleting gases have a cooling effect and aerosol particle pollution has a cooling effect.

Climate variability, climate oscillations, climate currents affect climate and are important to climate and are affected by global warming, but they are not the cause behind the recent rapid global warming.

Volcanoes and carbon emissions that are part of the carbon cycle are not adding to the carbon in the atmosphere. However, carbon emissions from burning fossil fuels do. If we didn’t burn fossil fuels Earth would be cooling.

Note : this does imply that our carbon emissions is a good thing. The rapid global warming we are witnessing is a very dangerous problem.

Other super facts related to global warming

To see the other Super Facts click here

Orbital Cycles are not the Cause of the current Global Warming

Superfact 122: We know that the current global warming, or if you call it Climate Change, or Climate Disruption, is caused by us primarily because of our burning of fossil fuels. It is not “natural causes”, and it is not orbital cycles, so called Milankovitch cycles. These orbital cycles include changes in orbital eccentricity, axial tilt, and axial precession.

Three illustrated orbital cycles. On the left orbital eccentricity, in the middle is the axial tilt and on the right axial precession. | Orbital Cycles are not the Cause of the current Global Warming — Illustration of Milankovitch cycles from MIT’s Climate Primer.

The evidence that the current rapid global warming is chiefly caused by our burning of fossil fuels is extensive and for all practical purposes conclusive. One of the steps towards understanding this evidence is understanding why no known natural cause of climate change can explain the current warming, and that includes orbital cycles. Therefore, this post is just one small step towards preparing you for the evidence that the current rapid global warming is chiefly caused by us. However, there is a lot of disinformation around this specific topic.

Hockey stick curve going back 1,000 years. The recent uptick in global temperature is very sharp and very sudden. — The so-called hockey stick curve depicting the last 1,000 years. The blue line is the first hockey stick curve ever created (by Michael Mann). He used proxy measurements such as tree rings, green-dots 30-year average, red temperature measurements. Wikimedia commons <<https://creativecommons.org/licenses/by-sa/4.0/deed.en>>. This graph is taken from this page.

Again, hockey stick curve going back 1,000 years. This time human causes and natural causes are indicated with a black respective a red shape. | Orbital Cycles are not the Cause of the current Global Warming — The so-called hockey stick curve depicting the last 1,000 years. In this graph I have indicated what part of the graph is climate change caused by natural causes respective climate change caused by human causes.

Very briefly; Earth’s orbital cycles, called the Milankovitch cycles are largely responsible for the ice ages, but they are not responsible for the current warming because the current warming is too rapid for the orbital cycles to be the cause, and the way the warming is happening is incompatible with how a warming caused by Milankovitch cycles would have happened. In addition, according to the Milankovitch cycles we should be cooling, not warming.

I am considering this a super fact because a lot of people have been fooled by the disinformation on this topic, and there is also a lot of gaslighting from less than reputable organizations and from politicians. They have bamboozled a lot of people. About 15 years ago, I was bamboozled by the disinformation myself. That was before I took the time to try to understand the topic. Understanding a topic, and understanding the evidence makes all the difference, and that is why climate scientists are near unanimous the world over that climate change / global warming is both real and caused by us.

Ask yourself, why would the climate scientists and the atmospheric physicists around the world, including scientists at NASA and NOAA, not investigate orbital cycles and other natural causes for climate change as a possible cause for our current warming? They are the experts on orbital cycles and past climate after all. We know that orbital cycles are not the cause of the current global warming, and this is important to know. Therefore, I think it is a super fact.

What Are Orbital Cycles?

One type of important type of climate forcing that’s been the cause behind the multiple ice ages that we’ve had over the last two million years are earth’s orbital cycles, or the Milankovitch cycles. There are primarily three orbital cycles, orbital eccentricity, change in axial tilt, and axial precession. Could they explain the current warming? No, they can’t because they are too slow, we are currently in a cycle that should be cooling the planet, and the way orbital cycles would warm the planet if they were responsible for the warming is very different from what we are witnessing.

Changes in Eccentricity

Earth’s orbit is not a perfect circle. Earth’s orbit varies from nearly circular to slightly elliptical and this change can cause climate change. This shift in Earth’s orbit takes place over periods of about 100,000 and 400,000 years. Click on the video from NASA below for an illustration of Earth’s eccentricity.

Changes in Obliquity (Tilt)

The angle Earth’s axis of rotation is tilted as it travels around the Sun is known as obliquity. Obliquity is why Earth has seasons. Over the last million years, it has varied between 22.1 and 24.5 degrees with respect to Earth’s orbital plane. The greater Earth’s axial tilt angle, the more extreme our seasons are. In addition, a larger tilt angle favor periods of deglaciation. The changes of Earth’s obliquity have a period of 41,000 years. Click on the video from NASA below for an illustration of the changes in obliquity.

Axial Precession (Wobble)

Earth wobbles slightly as it rotates, like a slightly off-center spinning top. The axis of Earth’s wobble changes slowly and is called axial precession. The corresponding cycle spans 25,771.5 years, or approximately 26,000 years. Click on the video from NASA below for an illustration of the changes in axial precession.

Video Explaining Earth’s Orbital Cycles

The video below from PBS gives an explanation and overview of earth’s three orbital cycles.

Orbital cycles are far too Slow to Cause the Rapid Global Warming Happening Today

The changes in Earth’s orbit and tilt operate over 20,000+ to 100,000-year periods, making Orbital Cycles unable to drive the sharp temperature spikes seen in a single century.

Orbital Cycles Predict Slow Cooling, not Rapid Heating

About 6,000 years ago Earth’s temperature was a bit warmer than it is today largely due to the climate fluctuations caused by orbital cycles. The warm period in the beginning of the Holocene epoch is referred to as the Holocene climatic optimum. Natural causes for climate change caused Earth’s temperature to slowly cool off until the recent very sudden uptick in average global temperatures.

Orbital Cycles are not the Cause of the current Global Warming — Temperature record for the last 150,000 years. Notice the sharp uptick towards the end. This picture is taken from this article.

The graph shows wild swings over the last 50,000 years and then a very sharp uptick at the end, which as indicated in the graph is caused by us. — Temperature record for the last 50,000 years. Notice the sharp uptick towards the end. I have circled natural and human caused causes for the climate change. This picture is taken from this article.

Below is a video that explains in greater detail why orbital cycles cannot explain the current warming. You can also read more about it here.

The Cooling of the Upper Atmosphere Tells Us the Current Warming is not Caused by Orbital Cycles or the Sun

Yes, the cooling of the upper atmosphere (specifically the stratosphere above the troposphere) is a key sign that current global warming is not caused by Milankovitch cycles or changes in the sun. Instead, observations show a warming lower layer (troposphere) and a cooling upper layer, which is the exact “fingerprint” of human-caused greenhouse gases. Other evidence that the warming is caused by greenhouse gases and not orbital cycles or the sun is the distribution of the warming across the globe and over time.

A Couple of Videos

The video below is a short one-minute overview of the causes behind global warming.

The video below from NASA is a bit longer, 13 minutes, but it gives a more detailed overview. Click here to see the page from where this is coming from.

Conclusion

We know that Orbital Cycles are not responsible for the current rapid global warming because Orbital Cycles operate on tens of thousands of years or hundreds of thousands of years, not a couple of centuries.

We know that Orbital Cycles are not responsible for the current rapid global warming because the effects of Orbital Cycles are slowly cooling Earth, not warming it.

We know that Orbital Cycles are not responsible for the current rapid global warming because if it was orbital cycles (or the sun) the upper atmosphere would not be cooling and the temperature increases would be distributed differently across Earth and distributed differently with respect to time.