The climate of our little blue planet has changed throughout its life, through natural causes. Timescales of these natural causes of climate change can be measured in hundreds and even millions of years, meaning it can take a long time for the effects to build and the effects stick around even longer until the next big shift.
Climate change is now heavily associated with global warming. However, across the history of planet earth, natural causes of climate change have lead to fluctuations (both up and down) in temperature and weather changes.
What are the natural causes of climate change? Well, several areas have been researched over the years including asteroid strikes, orbital changes, variations in solar output and volcanic activity. Let’s take a look at how these affect the climate.
- Volcanic Activity
- Solar Output
- Orbital Variations
- Internal Variability
Natural Causes of Climate Change
Available evidence strongly suggests that volcanic activity is a natural cause of climate change. However, the amounts produced by volcanoes is insignificant when compared to anthropogenic (a fancy word that means something that has come from or been caused by people) emissions. It is estimated by scientists that Volcanic eruptions produce 50 times less CO2 than humans do.
Interestingly, volcanoes actually have a mixed effect on our climate. Eruptions emit the greenhouse gas carbon dioxide (CO2) which causes global warming, but they also emit aerosol particles such as sulphur dioxide.
In 1991, the eruption of Mount Pinatubo, Philipines, emitted around 50 million tonnes of CO2 and threw a 20 million tonne cloud of sulphur dioxide into the stratosphere. Sulphate particles are known to be reflective and can block in the region of 5 to 10 percent of the sun’s warming energy. This single eruption caused an estimated 0.5oC of global cooling for almost 2 years.
Global volcanic activity also includes volcanic lakes, tectonic and hydrothermal areas, as well as emissions from mid-ocean ridges. Adding all of these emissions together. Adding all of these up, scientists estimated about 0.645 billion tonnes of CO2 is emitted per year, contributing to climate change. A seemingly tiny number compared to the 43.1 billion tonnes of CO2 produced by human activity in 2019.
It is widely accepted that the fluctuations in the output of radiation from the sun are connected to climate change. That being said, most climate scientists do not see a connection between these fluctuations in output and it being one of the natural causes of global warming.
Climate scientists agree that the sun follows an 11-year cycle. An increase in sunspots (which come and go) are associated with increased solar output. It has been calculated that at the height of an 11-year cycle, the global temperature rises by approximately 0.4%.
Between around 1650 – 1850 there were sustained periods of solar inactivity, which, mixed with other natural (and some human) reasons, caused the average temperature on earth to drop. This is known as the “Little Ice Age.”
During this time a grand minimum (Maunder Minimum) occurred where there were very few sunspots. Scientists have investigated the effects of another grand minimum, suggesting it could cool the planet by up to 0.3oC. This would not reverse human-caused global warming, merely slow it down and briefly offset it. Unfortunately, not the miracle that the planet currently needs.
About a century ago, Milutin Milanković, a Serbian geophysicist, gathered data that demonstrated the variances in the Earth’s orbit. Specifically, he was able to show that the orbit varies between being an elliptical to circular. The period in which fluctuations happen is thought to be over 100,000 years, and makes up part of what is known as The Milankovitch Theory.
The fluctuations include changes to:
- Eccentricity – the shape of Earth’s orbit (every 100,000 years)
- Obliquity – the tilt of the Earth’s axis (every 41,000 years)
- Procession – the ‘wobbling’ of Earth’s axis (every 26,000 years).
What does this mean for climate change?
Simply put, these changes in the Earth’s orbit mean that the distance between the planet and the sun changes. These small changes in distance happen over a very long period and this, in turn, affects the amount of solar radiation that reaches Earth.
Milankovitch theorised that the glacial periods on planet earth that occurred in the last 1,000,000 years, began when the three cycles aligned. So, favouring periods of increased solar radiation in the winter and decreased solar radiation in the summer caused the planet to dip into an ‘ice age’. The last ice age ended about 12,000 years ago. And the next ‘cooling cycle’ may occur in about 30,000 years time. A natural cause of climate change; just global cooling rather than global warming.
In 1978, a scientific study of deep-sea sediment cores found that the predictions made by Milankovitch did indeed correspond with periods of considerable climate change over the past 450,000 years. Meaning that it can be used like a climate time machine. To predict differences in solar radiation due to orbital variations over the next thousands of years.
Fun fact: the earth is currently tilted (obliquity) at an angle of 23.44o to the perpendicular plane of its orbital path.
There are some changes that occur to the Earth’s climate that have no external trigger. These types of changes are caused by factors and interactions with the climate system itself. One example of this phenomena is the El Niño–La Niña cycle.
This cycle causes temporary warming and cooling of the climate. They affect circulation patterns in the atmosphere and they can influence global climate.
El Niño raises the global temperature, while it’s ‘partner influencer’, La Niña, reduces it. The cycle repeats approximately every 5 years. The effects are short term, however, lasting just a few years.
Over the 4.54 billion year history of planet earth, asteroids have played a part in affecting our climate. When an asteroid strikes the earth, dust and debris particles are thrown into the upper atmosphere.
With the sun’s rays blocked, causing insolation to be reduced and the climate cools. This happens because energy from the sun is bounced back into space instead of coming straight through and warming the planet. The effect of this is immediate and quite profound. Well, look at what happened to the dinosaurs 66 million years ago!
Luckily, asteroids are a little like buses. You wait for what seems like aeons for one and then suddenly lots arrive in a short space (sorry) of time. If this is the case, it has been suggested that clusters of small asteroid strikes could also have had a significant impact on Earth’s climate.
Astrophysicists are currently gathering evidence which would seem to suggest that our planet, every once in a while, passes through areas of space that contain pockets of asteroids.
It is important to note that warming is not spread evenly in the Earth’s atmosphere. Scientists at NASA have observed, and reported, that the lower layers of the atmosphere have been warming while the upper layers have been cooling. This is in line with an increased greenhouse effect. Therein the problem lies.
The increased solar output does not take sides. It has the effect of warming all atmospheric layers, and not just the lower.
These are the main natural causes of climate change, some have more of an impact than others. But, they are natural phenomena regardless. Interested in learning more? Take a look at climate change quotes from scientists, adventures and celebrities.