Can Climate Change Happen Without Humans? The Science Says Yes.

Whether you accept the science of human-caused climate change or remain skeptical, there is one unavoidable truth: climate change can and does happen without any influence from human activity. The climate of our planet is not static or unchanging, but instead is dynamic and varies over timescales ranging from decades to millions of years. Even if humans never emerged and developed industrial societies, the Earth’s climate would still shift and evolve. While human activity may currently be amplifying and accelerating climate change, the natural factors that drive changes in the climate have been operating for eons and would continue regardless of humanity’s actions. Understanding how and why the climate can change under natural conditions is crucial to gaining a full perspective on the climate changes unfolding today.

What Causes Climate Change?

Climate change can occur due to natural factors, not just human activity. The climate has fluctuated dramatically over Earth’s history due to:

1. Changes in Earth’s orbit and axis. Cycles like Milankovitch cycles alter the amount of solar radiation that reaches the Earth, which can trigger ice ages and warm interglacial periods.
2. Changes in solar activity. Variations in the Sun’s activity, like sunspots and solar wind, can affect the amount of energy that reaches Earth. Changes in total solar irradiance of just 0.3% are enough to impact surface temperatures.
3. Release of greenhouse gasses. Natural events like volcanic eruptions emit carbon dioxide, methane, and other greenhouse gases that trap heat in the atmosphere. Massive and sustained volcanic activity in the past caused substantial global warming.
4. Changes in ocean circulation. Variations in ocean currents, like the Atlantic meridional overturning circulation, redistribute heat and carbon dioxide around the planet. A slowing of ocean circulation in the past led to climate change in certain regions.
5. Natural changes in the biosphere. The natural decay and burning of forests and other vegetation emit carbon dioxide and methane. Some scientists believe changes in vegetation and wildfires during the last deglaciation contributed to rising CO2 levels.

In summary, Earth’s complex climate system is influenced by astronomical, geological, and ecological factors in addition to human activities. However, the current rapid rate of increase in global temperatures cannot be explained by natural causes alone. The consequences of anthropogenic climate change pose severe risks, so action must be taken to curb greenhouse gas emissions and allow natural factors to once again dominate climate fluctuations.

The Greenhouse Effect Explained

To understand how climate change can happen without human activity, you must first understand the greenhouse effect. The greenhouse effect refers to gasses in the atmosphere that trap heat.

• Naturally occurring greenhouse gasses include carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O). These gasses allow most of the light from the sun to pass through the atmosphere to warm the surface of the Earth. However, they trap the heat radiated back from the surface, causing the planet’s surface temperature to be warmer than it would otherwise be.

This natural greenhouse effect is necessary for life as we know it. Without it, Earth’s average surface temperature would be below freezing. However, human activities like burning fossil fuels have caused greenhouse gas concentrations to increase dramatically, enhancing the greenhouse effect and warming the planet to dangerous levels.

While humans are exacerbating the greenhouse effect, climate change can also happen due to natural causes. For example:

1. Changes in Earth’s orbit and axis can alter the amount of solar energy reaching the planet. When less energy reaches Earth during the summer, glacial periods can occur.

2. Major volcanic eruptions can emit sulfur gasses that block out sunlight and cool the planet. Massive volcanic activity in the distant past caused major climate disruptions.

1. Natural changes in ocean circulation patterns can also influence climate. For example, changes in the Gulf Stream can alter the climate in western Europe and eastern North America.

In summary, while natural factors can influence Earth’s climate and have caused climate change in the past, the increased concentrations of greenhouse gasses from human activities are the primary cause of current global warming according to the scientific consensus. Reducing greenhouse gas emissions is critical to mitigating the worst consequences of climate change.

Natural Climate Change vs Current Warming Trends

While the Earth’s climate has changed throughout history, the current warming trend is of particular concern because it is changing at an unprecedented rate. To understand why, it’s important to recognize the difference between natural climate change and human-caused climate change.

Natural Climate Change

The climate has fluctuated between ice ages and warm interglacial periods over millions of years due to small variations in Earth’s orbit and axis. These gradual shifts caused glaciers to advance and retreat, sea levels to rise and fall, and global average temperatures to increase and decrease. Natural factors like volcanic eruptions and solar activity also caused shorter-term climate changes. However, the rate of temperature increase over the past century is faster than anything we have seen in the past 1,000+ years.

Current Warming Trends

Today’s climate change is dominated by human activities that release heat-trapping greenhouse gasses into the atmosphere, primarily carbon dioxide (CO2) and methane (CH4). As we burn fossil fuels for energy and transportation, clear forests for agriculture, and raise livestock, the amounts of CO2 and CH4 in the atmosphere have skyrocketed to levels not seen in at least 800,000 years. These gasses trap more of the sun’s heat, causing surface and ocean temperatures to rise, ice to melt, and sea levels to increase at an accelerated pace.

While natural factors are still at play, human-caused climate change from increased greenhouse gas emissions is the primary driver of the rapid warming seen today according to the world’s leading climate science organizations. Urgent action is needed to curb emissions and limit the worst consequences of climate change. Our planet’s future depends on transitioning from fossil fuels to renewable energy and making our societies and infrastructure more sustainable and eco-friendly. Together, we can rise to meet this urgent challenge.

How Earth’s Orbit and Rotation Impact Climate

The Earth’s orbit and rotational changes impact the climate over long periods of time through astronomical forcing. As the planet revolves around the sun, several factors affect the amount of solar radiation that reaches the Earth, influencing global temperatures and climate patterns.

Orbital Eccentricity

The Earth’s orbit changes from nearly circular to slightly elliptical over cycles of around 100,000 and 400,000 years. An elliptical orbit means the Earth is closer to the sun at some points, increasing the solar radiation received. This variation directly impacts the intensity and distribution of sunlight falling on the planet, altering atmospheric circulation and surface temperatures.

Axial Tilt

The tilt of the Earth’s axis also varies between 22.1 and 24.5 degrees over approximately 41,000 years. Known as obliquity, a greater tilt means the poles receive more direct sunlight during summer, increasing the temperature difference between the equator and poles. This temperature gradient drives atmospheric and ocean circulation, as well as monsoonal systems. Changes in axial tilt, therefore, lead to shifts in wind and precipitation patterns that can influence climate.

Precession

The slow change in the orientation of the Earth’s axis, known as precession, alters which hemisphere experiences summer during perihelion, the point in the orbit where the planet is closest to the sun. Perihelion currently occurs during the Northern Hemisphere winter, but precession causes it to shift through the seasons over cycles of around 23,000 years. When perihelion aligns with summer in the Northern Hemisphere, that hemisphere receives more solar radiation during the warmer months, modifying global climate patterns.

While subtle, these astronomical changes have major impacts on climate over long timescales. By altering the amount of solar radiation distributed across the planet and driving shifts in atmospheric circulation, the Earth’s orbital parameters and rotational dynamics lead to natural changes in global temperatures and climate, independent of human activity. Understanding these astronomical forcing mechanisms provides context for natural climate variability and helps distinguish between anthropogenic and non-anthropogenic climate change.

The Role of the Sun in Climate Change

The sun is the primary source of energy for Earth’s climate system. Variations in the sun’s intensity can influence the climate on Earth. Scientists have found correlations between sunspots, solar flares, and other solar activity with changes in Earth’s climate on timescales from decades to millennia. However, the sun alone cannot explain the rapid increase in global temperatures observed since the Industrial Revolution.

Changes in Solar Irradiance

The amount of solar energy that reaches Earth, known as total solar irradiance (TSI), varies over timescales from minutes to millennia. Variations in TSI of around 0.1% over 11-year solar cycles and longer-term variations of a few tenths of a percent may influence Earth’s climate. However, satellite measurements show that the variations in TSI are too small to explain the pronounced rise in global surface temperatures over the past century.

Solar Forcing of Climate Change

Scientists have found a link between lower solar activity (as measured by sunspots) during the Maunder Minimum in the 1600s and the colder European climate at that time, known as the Little Ice Age. However, the temperature changes were regional, not global. The increase in atmospheric CO2 since the Industrial Revolution has caused a global temperature increase much larger than any climate change that can be linked to variations in solar activity.

While the sun is the dominant source of energy for Earth’s climate system and variations in solar activity may influence climate on timescales from decades to millennia, the rapid increase in global surface temperatures observed since the Industrial Revolution cannot be explained by changes in solar irradiance alone. Natural factors cannot explain the consistent warming that has occurred around the globe over many decades. The increased CO2 in the atmosphere from human activities is the dominant cause of the ongoing rise in Earth’s temperature according to the scientific consensus. Monitoring changes in both natural and human factors that can influence climate is critical to better understanding climate change.

Volcanic Eruptions and Climate Change

Volcanic eruptions can have a significant impact on the climate, both regionally and globally.

Ash and Gas Emissions

When a volcano erupts, it spews large amounts of ash, gasses like sulfur dioxide, and other particles into the atmosphere. The ash and gasses block sunlight from reaching the Earth’s surface, cooling the climate. Historic eruptions like Tambora in 1815 and Krakatoa in 1883 caused global temperatures to drop up to 1°C (1.8°F) the following year.

Stratospheric Injections

Powerful volcanic eruptions can inject sulfur gasses and ash into the stratosphere, the layer of the atmosphere extending from about 6 to 30 miles high. Materials injected into the stratosphere can remain for years, spreading around the globe. Stratospheric injections cause more widespread and long-lasting climate impacts.

Cooling Effects

Volcanic eruptions cool the climate through several mechanisms:

• Ash and gasses reflect sunlight back to space, reducing the amount of solar radiation reaching the Earth.
• Ash and gasses absorb heat in the atmosphere, reducing the amount of longwave radiation escaping to space. This disrupts the greenhouse effect and causes atmospheric cooling.
• Ash and gasses provide surfaces for chemical reactions that destroy ozone, a potent greenhouse gas. Ozone depletion allows more heat to escape to space, cooling the climate.
• Ash and gasses alter atmospheric circulation patterns, impacting heat transport and weather systems. These changes can influence surface temperatures, precipitation patterns, and storm tracks.

While massive volcanic eruptions are rare, they show us that natural factors alone can cause disruptions to the climate system. However, the climate changes currently underway are largely due to human activity, not natural factors like volcanic eruptions. By reducing greenhouse gas emissions and transitioning to renewable energy, we can mitigate and adapt to the changes already set in motion.

Changes in Earth’s Orbit and Rotation Over Time

Earth’s orbital changes and variations in its rotation and axis over timescales of tens to hundreds of thousands of years can lead to shifts in climate that are independent of human activity.

Orbital Eccentricity

The orbit of the Earth around the Sun is not perfectly circular but slightly elliptical or “eccentric.” As the orbit becomes more or less elliptical over time, the amount of solar radiation reaching the Earth changes. Greater eccentricity leads to more variation in solar radiation between seasons and can alter patterns of glaciation. Over about a 100,000-year cycle, changes in Earth’s orbital eccentricity are thought to be a key factor in the recurrence of ice ages.

Axial Tilt

The tilt of Earth’s axis relative to the plane of its orbit, also known as “obliquity,” varies between about 22 and 24 degrees over a cycle of about 41,000 years. Greater axial tilt increases the difference in solar radiation received by the two hemispheres in their respective summers. This can strengthen monsoons and alter circulation patterns in the oceans and atmosphere, influencing global climate.

Precession

Like a spinning top, the orientation of Earth’s axis slowly rotates or “processes” over a cycle of about 26,000 years. This alters which hemisphere receives more solar radiation during specific seasons. For example, currently, the Northern Hemisphere receives more solar radiation during summer because it is pointed toward the Sun. But in about 13,000 years, this will be reversed. Such changes are thought to influence the timing and intensity of glacial periods over the last million years or so.

While subtle and cyclic, changes in Earth’s orbit and rotation over millennia can significantly impact global climate, even in the absence of human activity. By altering patterns of solar radiation and the distribution of energy across the planet, these celestial motions represent a natural mechanism for climate change that has operated over Earth’s history.

Natural Changes in Atmospheric CO2 Levels

Natural Fluctuations in the Carbon Cycle

The Earth’s climate has changed throughout history due to natural factors that influence atmospheric CO2 levels and temperature. These natural fluctuations in the carbon cycle and other processes can lead to climate change without human activity.

The oceans, vegetation, and weathering of rocks are all part of the carbon cycle that impacts CO2 levels. As CO2 is released and absorbed by these natural processes, it causes the atmosphere to gain or lose CO2 over time. For example, as ocean temperatures rise, the water cannot hold as much CO2, so it releases some into the air. Similarly, as temperatures drop, the oceans absorb more CO2 from the atmosphere.

Variations in the Earth’s orbit and axis can also alter the amount of solar radiation that reaches the Earth, influencing temperature and climate. Over thousands of years, changes in Earth’s orbit have led to cyclical fluctuations between ice ages and warm periods. These Milankovitch cycles trigger natural climate change as the Earth gains or lose heat and atmospheric CO2 fluctuates.

Volcanic Eruptions

Volcanic eruptions can emit CO2, sulfur dioxide, and other gasses that lead to climate change. Massive volcanic eruptions, in particular, can alter climate by releasing gasses and ash that block sunlight and warm the planet. For example, the 1991 eruption of Mount Pinatubo in the Philippines released enough sulfur dioxide to reduce global temperatures by 0.5°C for a few years.

While natural factors drove climate change long before humans, human activity now overwhelms these natural causes. By burning fossil fuels, deforestation, and industrialization, humans have caused CO2 levels to rise higher and faster than ever before. According to scientists, human-caused climate change poses severe threats if left unaddressed. By understanding both natural and human causes of climate change, we can work to curb human impacts and build a more sustainable future.

Climate Change Without Humans FAQs: Answering Your Most Common Questions

Climate change is an ongoing process that has occurred throughout Earth’s history. While human activity has sped up current global warming trends, climate change can and does happen without human influence as well. Here are some frequently asked questions about climate change without humans:

What natural factors drive climate change?

Several natural factors contribute to climate change in the absence of humans:

• Variations in Earth’s orbit and axis: Changes in Earth’s orbit and the tilt of its axis impact the amount of sunlight that reaches the planet. These variations are known as Milankovitch cycles and they trigger ice ages and warm interglacial periods.
• Solar activity: Changes in the Sun’s activity, including brightness and solar wind, can influence the amount of radiation that reaches Earth which contributes to temperature changes and impacts climate.
• Volcanic eruptions: Massive volcanic eruptions release sulfur gasses and ash that block out sunlight and lead to temporary cooling. When the effects clear, greenhouse gasses from the eruption can cause some warming.
• Ocean circulation: Changes in ocean circulation patterns, such as fluctuations in the Gulf Stream, alter heat distribution and transport around the planet. This can lead to regional climate changes.

How fast can the climate change without humans?

Climate change from natural factors alone usually occurs gradually over long timescales of tens to hundreds of thousands of years. This allows most species to adapt to the changes. However, at times rapid climate change has occurred in just a few decades. For example, average temperatures rose by as much as 10°C in some regions following massive volcanic eruptions, though these effects were short-lived.

What effects did past climate change without humans have?

Past climate change uninfluenced by humans has had effects like:

• Glacial and interglacial periods during ice ages with associated sea level changes.
• The warming and cooling of the planet caused shifts in ecosystems and the geographical distribution of plants and animals.
• Desert expansion and changes in aridity during certain periods impacted human civilizations.
• Temporary cooling following large volcanic eruptions led to lower global temperatures for a few years.

While natural factors alone can drive climate change, the speed and severity of current global warming trends are due primarily to human activity like burning fossil fuels. However, understanding past climate change can provide insights into our planet’s sensitivity and help us better predict future impacts.

Conclusion

As this article has shown, natural factors have caused substantial climate changes throughout Earth’s history. The mechanisms behind these changes demonstrate that global warming and cooling can indeed occur independently of human activity. The fluctuations in Earth’s orbit and axis, variations in solar activity, volcanic eruptions, and other natural forces have significantly impacted the climate for millennia. While humans are now contributing to current climate change through greenhouse gas emissions and other activities, the climate system is complex with many interacting parts. Science clearly shows that nature itself is fully capable of altering the climate without our help. Understanding how climate has changed in the past helps inform scientists about how it may change in the future, regardless of humanity’s actions. Though we may not be able to prevent natural climate change, we can make choices that reduce our own impact and allow us to adapt to whatever changes come our way.