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Climate Change Causes

Climate Change Causes

Climate change causes can be split into long-term and short-term causes. Many natural factors cause long-term climate change, including solar variation, greenhouse gasses, and tectonics. Solar output variation used to cause significant short-term effects in climate change, but human activity negates its significance. Volcanic activity and ENSO cycles can cause short-term changes in the climate.

Natural climate change causes

In the twentieth century, the mathematician Milutin Milanković observed variations in the Earths orbital movement. He hypothesised that these variations could explain the Earth’s long-term climatic changes and oscillations between the glacial and interglacial conditions. These long-term changes are natural climate change causes, as they are normal changes that our planet goes through.

He observed three cycles, which later became known as the Milankovitch or Milanković cycles. They are eccentricity, obliquity and precession.

Natural climate change causes: Eccentricity

The phase where the Earth is closest to the Sun is called perihelion, while the furthest state is known as aphelion. The difference between perihelion and aphelion determines the measure of eccentricity.

Eccentricity measures the extent of the Earth’s departure from a perfectly circular orbit.

The Earth is currently in a low-eccentric shape. There is only a 3% difference in distance to the Sun at aphelion and perihelion, which causes about a 7% difference in solar radiation received during the two phases. During high eccentricity, the distance to the Sun at aphelion and perihelion can vary by 10%. This results in about a 25% disparity in the solar radiation received during the two phases.

Climate change casues, earth eccenticity, StudySmarterFig. 1 - The Earth is currently experiencing low eccentricity, meaning the difference in aphelion and perihelion is almost a circle

Eccentricity causes variations in season lengths, e.g. the Northern Hemisphere experiences summers that are four days longer than winters and springs that are approximately three days longer than autumns. As eccentricity decreases, seasonal variations even out.

Eccentricity’s effect on the climate is very small in the short term. In the long term, it can account for some temperature variations. However, the effect of eccentricity alone is far too small to account for the observed long-term changes in the Earth’s climate.

Natural climate change causes: Obliquity

Obliquity refers to the angle of the Earth’s axis with respect to its orbital plane. This is also known as tilt.

Over the last million years, the angle has varied between 22.1 and 25.5 degrees to the orbital plane. The greater the angle of the tilt, the more extreme the seasons. This is because each hemisphere will be more exposed to solar radiation during its Summer and less exposed during the Winter. Larger tilt angles correlate to interstadials, but these effects are not globally uniform, meaning they don’t occur everywhere to the same extent. The current angle is around 23.4 degrees (halfway between the extremes) and is slowly decreasing. This decrease is currently causing

  • milder seasons
  • increasingly warmer winters
  • cooler summers
  • increased high-latitude ice cover

The tilt effect is noticeable over very large time scales (around 41,000 years) but not in any shorter time scales. As a result, it is not enough to account for the rates of global climate change in recent years.

Natural climate change causes: Precession

Precession is also known as wobble. As the Earth rotates, it moves off-axis slightly and shifts its angle relative to its centre. This cycle spans approximately 26,000 years.It has numerous long-term effects on climate change:

  • Precession makes seasonal contrasts between the Northern and Southern Hemispheres more extreme.
  • Currently:
    • Perihelion occurs during the Winter in the Northern Hemisphere.
    • Perihelion occurs during the Summer in the Southern Hemisphere.

Consequently, summers in the Southern Hemisphere are hotter, and the Northern Hemisphere experiences moderate seasonal variations.

However, in 13,000 years, this effect will be reversed due to the change in precession, resulting in more extreme summers in the Northern Hemisphere and more moderate seasonal variations in the Southern Hemisphere.

While precession increases the disparity between seasons in the two hemispheres, its immediate effect on global climate change is relatively small. It is nonetheless important to consider the bigger picture when considering the causes of long-term climate change.

More natural causes of climate change

Another natural cause of climate change is solar output variation.

Solar output variations are the differences in the amount of thermal energy output by the Sun. This is caused by natural solar evolution and the activity of its magnetic field.

While modern-day techniques allow us to measure and reconstruct solar output in quantified terms (the standard unit for solar output is solar iridescence measured in Watts per metre squared), intentional observations of sunspots can be dated back to 364 BCE.

Natural climate change causes: Sunspots

Solar activity can be correlated with the number of sunspots observed on the Sun. Sunspots are likely caused by concentrations of magnetic field flux that inhibit convection in the area, which is believed to reduce luminosity – hence sunspots look like dark patches on the sun.

Causes of Climate Change Sunspots StudySmarterFig. 2 - Sunspots

It is important to note, however, that the interactions and mechanisms of the Sun’s magnetic field causing the sunspots are not fully understood. We only have a general idea of how they occur. A greater number of sunspots indicates intense solar activity and, therefore, higher solar output, which would suggest higher temperatures due to the increased thermal energy received by the Earth.

Sunspots were first observed through a telescope in the early seventeenth century. As a result, we have extensive records of solar activity available to us to weigh up against historical records of the global climate.

Maunder Minimum

During the Little Ice Age (1650–1750), very few sunspots were observed, suggesting decreased solar activity. The periods where solar activity decreases are known as the Maunder Minimum. Studies suggest that a Maunder Minimum could be responsible for the cooling of up to 0.3°C in the times before the Industrial Revolution when the Carbon Cycle was largely in balance. Small decreases in temperature could have caused feedback loops that, in turn, greatly affected climate. Therefore, it is hypothesised that the Maunder Minimum around the time of the Little Ice Age could have caused the Ice Age or at least largely contributed to it.

Does solar activity contribute to climate change?

In modern days where human activity causes significant increases in climate change (estimated to have caused a direct increase of 0.65°C since 1950 globally), a decrease of 0.3°C may slow down warming. While it may be argued that solar activity was significant in the past, in the modern context, it doesn’t play a significant role in the change in the global climate.


Long-term climate change causes

It may have come as a surprise that we went into depth learning about the three Milankovitch cycles only to say in each case that they have a small immediate effect on global climate change. So why are they significant to this topic?

While these 100,000-year cycles may only cause a 0.5°C to 1°C change, the feedback loops they cause are largely responsible for long-term changes in the climate.

What is a feedback loop?

A feedback loop is when one effect causes another effect. This will either increase or decrease the original effect, e.g. effect A causes effect B, and effect B will either increase or decrease the severity of effect A.

  • If effect B increases the severity of effect A, then it is a positive feedback loop. Effect A will then be more severe and cause more instances of effect B, which further increases affect A and so on.
  • On the other hand, if effect B decreases effect A, then it is a negative feedback loop. Effect A will be less severe and could potentially be cancelled out by effect B.

What feedback loops occur due to Milankovitch cycles?

If Milankovitch cycles cause a decrease in temperature (even a small change), then:

  • The lower temperatures (e.g. from increased eccentricity) increase the rate of glacial advance, i.e. more surface ice.
    • The increase in surface ice increases the albedo effect.
      • This means the Earth absorbs less solar radiation and consequently does not increase in temperature as much as it otherwise would.
  • The increase of the albedo effect causes further decreases in temperature.
  • The cycle continues from the first listed bullet point.

Natural short-term climate change causes

Let's take a look at some natural short-term climate change causes:

Volcanic activity has been known to cause significant global cooling for short periods of time (on a climatic time scale). Volcanic eruptions cause massive emissions of particulates such as sulphur dioxide (SO₂) that are injected into the atmosphere. These particulates can stay in the atmosphere for up to three years. They can subsequently form sulphur aerosols, which increase the reflection of solar radiation within the atmosphere, stopping the solar radiation from heating the Earth, hence causing cooling in the Earth’s lower atmosphere.

Note that sulphur dioxide may, in some cases, be considered an indirect greenhouse gas.

The effect of volcanic eruptions on global cooling was evident in the eruption of Mount Tambora in 1815. This was one of the most powerful eruptions in recorded history and was followed by accounts of very cold weather soon after the eruption. Though Mount Tambora is in southern Indonesia, in the same year, a persistent dry fog was seen in the northeastern United States.

This phenomenon is known as global dimming, a sign of the aforementioned SO2 ejected into the atmosphere. The effects of global dimming led to stormier and more intense winters globally, leading to failed harvests and disastrous food shortages. It is estimated that global temperatures decreased between 0.4°C and 0.7°C globally. The subsequent year was dubbed 'Year without a Summer' due to the significant cooling effects caused by the eruption.

The El Niño Southern Oscillation (ENSO) cycle and short-term climate change

The ENSO cycle is a switch between two states known as El Niño and La Niña. It has effects on short-term climate change. ENSO occurs every two to eight years. El Niño (9-12 months ) is typically shorter than La Niña (9 months- 2 years) and occurs more often than La Niña. The transition between states is called neutral conditions.

El Niño is when a warming of the ocean surface in the central and eastern Pacific Ocean occurs, usually caused by the weakening of easterly winds.

Areas of the ocean that face increased temperatures also face increased rates of evapotranspiration, causing significantly higher moisture levels. This means more condensation and, therefore, rainfall.

The other half of the ENSO cycle is La Niña

La Niña can be roughly viewed as the opposite of El Niño. During La Niña, the warm mass of water in the Pacific is pushed westwards towards the coast of eastern Australia. This means that a cooling of the ocean surface in the central and eastern Pacific occurs.

As a result, the areas of the west Pacific increase in rainfall due to increased evapotranspiration in the area, while the east Pacific faces increased droughts.

El Niño Effects

The areas most affected by increased rainfall are:

  • South America
  • Southern USA
  • Canada

While precipitation increases in those areas, others experience drought. These include:

  • Eastern Australia and West Pacific
  • Southern Africa

La Niña effects

The areas most affected by increased rainfall are:

  • American Midwest & Northern California
  • Southern & Eastern Africa
  • Australia
  • South-east Asia

While precipitation increases in those areas, others experience drought. These include:

  • Central Africa
  • Parts of South America (Peru & Chile)

The effect of the ENSO cycle on Europe's climate is not as apparent as it is in South America.

Anthropogenic causes of climate change

So far, we have focused on the natural causes of climate change. However, anthropogenic (or human) causes of climate change are now the main driving cause of climate change. This includes; burning fossil fuels, deforestation and over-farming.

Greenhouse gas levels have fluctuated throughout the Earth’s history. These fluctuations have varied greatly.* High levels of greenhouse gases cause the greenhouse effect, and the greenhouse effect will also cause both positive and negative feedback loops.

Positive feedback loop

  1. Increased greenhouse gases lead to increased temperatures.
  2. Oceans absorb more CO2, increasing their overall heat and acidity levels.
  3. This can likely cause a decrease in phytoplankton, which is a major carbon sink (believed to be responsible for at least 30% of the Earth’s carbon sequestration/absorption).
  4. Less CO2 is absorbed, and more ends up in the atmosphere, increasing the greenhouse effect.

Negative feedback loop

  1. Increased greenhouse gases in the atmosphere.
  2. Increases in CO2 lead to greater vegetation cover.
  3. Increased carbon sequestration leads to lower CO2 levels.

* Please note that the above only refers to the non-enhanced greenhouse effect. It does not go against the consensus on human-caused/accelerated climate change. This is covered extensively in the Carbon Cycle.

Climate change causes diagram

Looking into the differences in severity between natural causes of climate change and anthropogenic or human causes of climate change can be jarring. What becomes clear is that we are having a significant impact on our climate, specifically the rise in global temperature.

Climate change consequences

There are many consequences to climate change. From rise and fall in temperature to longer or shorter seasons. Plate tectonics and their consequences on the global climate are not often thought about when discussing long-term climate change. Plate tectonics contribute a lot to global change in climate, but much of the best-known tectonic effects contribute to short-term climate change. There is, however, one geological event that is believed to have led to the formation of the Greenland ice sheet. Over three million years ago, the North and South American continents had a gap between them. This allowed Thermohaline Circulation currents to flow between them (these are currents of warm water travelling through large water masses). At this point, the Gulf Stream didn’t exist, and northern ice masses were considerably smaller.

However, about three million years ago, the two American continents collided, causing the formation of the Panama Isthmus. This forced the warm current to move towards northern Europe to create the Gulf Stream. This significantly increased evaporation rates in the colder northern climates.

As a result, there would have been increased snowfall and ice formation, which would have increased the surface ice cover. Recall the positive feedback loop of the Milankovitch cycles in the previous section. Increased ice cover could have caused a similar effect (the albedo effect). It is widely believed that this event could have kickstarted the Greenland ice age and significantly decreased global temperatures.

Climate Change Causes - Key takeaways

  • Many natural factors cause long-term climate change, including solar variation, greenhouse gases, and tectonics.

  • Sometimes, the secondary effects of these causes lead to large-scale changes.

  • Feedback loops are essential to explain large-scale changes in the global climate.

  • Solar output variation causes significant effects, but human activity negates its significance.

  • Volcanic activity, though rare, can cause extreme short-term variations in climate.

  • ENSO cycles are relatively frequent and cause changes in the climate globally.


References

  1. Fig. 1: Eccentricity diagram (https://commons.wikimedia.org/wiki/File:Perihelion-Aphelion.svg) by Chris55 (https://commons.wikimedia.org/wiki/User:Chris55) licensed by CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/deed.en)
  2. Fig. 2: Sunspots (https://www.flickr.com/photos/gsfc/15430820129/) by NASA Goddard Space Flight Center (https://www.flickr.com/people/24662369@N07) licensed by CC BY 2.0 (https://creativecommons.org/licenses/by/2.0/deed.en)

Frequently Asked Questions about Climate Change Causes

A natural cause of climate change is Earth’s eccentricity. Eccentricity’s effect on the climate is very small in the short term. In the long term, it can account for some temperature variations. However, the effect of eccentricity alone is far too small to account for the observed long-term changes in the Earth’s climate.

Some human causes of climate change are any activities (such as the burning of fossil fuels) that release greenhouse gases. High levels of greenhouse gases cause the greenhouse effect. 

Human activity causes significant climate change. Increases in greenhouse gases from human activity has caused increases in global temperatures. Natural causes such as solar activity do not play a significant role in climate change.

While climate change has the potential to damage, or completely destroy ecosystems, and may cause a mass extinction, it does not seem likely that humans will go extinct from climate change alone. However, severe climate change will make life much more challenging for humans- if we do nothing to stop climate change, we may be on track for extinction. 

With the proper management strategies (such as switching to renewable energy sources, recycling, biking to school or work instead of driving), we may be able to slow the effects of climate change or even prevent it!

Climate change does not cause air pollution itself, but rather, air pollution as a result of human activities can cause climate change. Air pollution such as smog increases the greenhouse effect, which is a cause of global warming.

Final Climate Change Causes Quiz

Question

What does eccentricity measure?

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Answer

Eccentricity measures the earth’s departure from a perfectly circular orbit.

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Question

What is the name of the phase where the earth is closest to the sun?

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Answer

The name of the phase where the earth is closest to the sun is known as perihelion.

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Question

What is the name of the phase where the earth is farthest from the sun?


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Answer

The phase where the earth is farthest from the sun is known as aphelion.

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Question

How long does it take for the earth to move from perihelion to aphelion or vice-versa?


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Answer

It takes 100,000 years for the earth to move from perihelion to aphelion and vice-versa.

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Question

What is obliquity?


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Answer

The angle of the earth’s axis with respect to its orbital plane

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Question

What is correlated with larger obliquity angles?


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Answer

Interstadials are correlated with larger obliquity angles.

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Question

What is precession?

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Answer

Precession is the shift in the earth’s angle on its axis relative to its center.

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Question

What are the long-term effects of precession?

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Answer

Greater precession makes seasonal contrasts between the two hemispheres more extreme.

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Question

What temperature changes are Milankovitch cycles immediately responsible for?


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Answer

Milankovitch cycles are immediately responsible for 0.5 to 1 degrees Celsius temperature changes. 

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Question

Why are Milankovitch cycles relevant despite their small immediate effect?

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Answer

Feedback loops magnify the effects of these temperature changes.

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Question

What effect causes an increase in reflected solar rays?

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Answer

The albedo effect.

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Question

Name an event when tectonics caused a long-term change in the global climate.

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Answer

The collision of the two American plates blocked the thermohaline circulatory currents and formed the Panama Isthmus.

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Question

Name the estimated range of CO2ppm throughout the earth’s history.

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Answer

200ppm and 5000ppm.

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Question

What do increased sunspots indicate?

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Answer

Increased sunspots indicate increased solar activity.

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Question

What is the Maunder Minimum?


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Answer

The Maunder Minimum is a period of decreased solar activity.

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Question

What are the effects of El Niño?


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Answer

  • Increased precipitation 
    • South America
    • Southern USA
    • Canada
  • Decreased precipitation 
    • Eastern Australia and West Pacific

    • Southern Africa  

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Question

What are the effects of La Niña?

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Answer

  • Increased precipitation
    • American Midwest & Northern California 
    • Southern & Eastern Africa
    • Australia
    • South-east Asia
  • Decreased precipitation 
    • Central Africa
    • Parts of South America (Peru & Chile)

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Question

Name a volcanic event responsible for significant cooling.

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Answer

Mount Tambora, 1815. Temperatures decreased between 0.4-0.7 degrees Celsius globally.

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Question

What is the estimated direct contribution of solar output variation on global temperatures?


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Answer

The estimated direct contribution of solar output variation on global temperatures is a decrease in temperature of up to 0.3 degrees Celsius. 

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Question

How can volcanic eruptions cause a change in climate?

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Answer

Global dimming blocks solar radiation and hence the earth’s direct source of heat is inhibited.

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Question

What is the time period of ENSO cycles?


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Answer

The time period of ENSO cycles is two to eight years.

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