Exploring the Causes of Climate Change

Climate change is one of the most pressing challenges of our time, and understanding its causes is the first step toward addressing it. The Earth’s climate has always changed – but the pace at which it’s changing now is unprecedented. So what’s driving this rapid shift? The answer involves a mix of human activities, natural phenomena, and changes in how Earth manages its energy budget. Let’s break it down.

Greenhouse gases: the primary human-driven cause 🔗

The greenhouse effect is essential for life on Earth. Certain gases in the atmosphere – known as greenhouse gases (GHGs) – trap heat radiated from the Earth’s surface and re-emit it in all directions, including back toward the ground. Without these gases, Earth’s average surface temperature would be about −18°C instead of the livable 15°C we experience today. The problem begins when human activities push the concentrations of these gases far beyond their natural levels.

Carbon dioxide (CO₂) 🔗

Carbon dioxide is the single largest contributor to human-caused warming. It is released primarily through the burning of fossil fuels – coal, oil, and natural gas – for electricity, heat, transportation, and industrial processes. Deforestation also plays a role, since trees absorb CO₂, and cutting them down releases stored carbon back into the atmosphere. According to NOAA, atmospheric CO₂ reached a record global average of 422.7 parts per million (ppm) in 2024, which is roughly 50% higher than pre-industrial levels. The annual rate of increase over the past 60 years has been about 100 times faster than natural increases seen at the end of the last ice age.

CO₂ is also Earth’s most important long-lived greenhouse gas. It persists in the atmosphere for centuries, meaning emissions today will continue warming the planet for generations. Additionally, the ocean absorbs a significant portion of CO₂, which lowers its pH – a process known as ocean acidification – threatening marine life that depends on calcium carbonate to build shells and skeletons.

Methane (CH₄) 🔗

Methane is a far more potent greenhouse gas than CO₂ in the short term, though it has a shorter atmospheric lifetime of about nine years. It comes from both natural and human-caused sources. Natural wetlands produce methane through the decomposition of organic matter, while human sources include livestock digestion, rice paddies, landfills, and leaks during fossil fuel extraction and transportation. Natural gas itself is composed of 70% to 90% methane. Global methane emissions have risen by nearly 30% between 1990 and 2024, according to the EDGAR emissions database.

Nitrous oxide (N₂O) 🔗

Nitrous oxide is another long-lived greenhouse gas. It is released primarily through agricultural activities – particularly the use of synthetic and organic fertilizers – as well as from burning fossil fuels and vegetation. Its atmospheric concentration has increased by about 34% since 1990. Although emitted in smaller quantities than CO₂, nitrous oxide is roughly 270 times more effective at trapping heat per molecule over a 100-year period, making it a significant contributor to overall warming.

Fluorinated gases and other contributors 🔗

Fluorinated gases, including chlorofluorocarbons (CFCs), hydrofluorocarbons (HFCs), and perfluorocarbons, are entirely industrial in origin. While they exist in much smaller concentrations, some of these compounds have a warming potential up to 23,000 times greater than CO₂. Their atmospheric concentrations have increased by over 300% since 1990. Though their total contribution to warming is smaller than CO₂ or methane, their extreme potency makes them a significant concern.

Where do greenhouse gas emissions come from? 🔗

Understanding the sectors responsible for emissions helps clarify how deeply fossil fuels are embedded in modern life. According to the United Nations, the major sources include:

Energy and electricity production accounts for the largest share. Most electricity worldwide is still generated by burning coal, oil, or gas, which releases both CO₂ and nitrous oxide. Industry and manufacturing is another major source, driven by fossil fuel energy used to produce cement, steel, plastics, and other materials. Transportation – cars, trucks, ships, and aircraft – contributes nearly one-quarter of global energy-related CO₂ emissions, mostly from petroleum-based fuels. Agriculture and food production generates emissions from livestock, fertilizer use, deforestation for farmland, and fossil fuel-powered equipment. In 2024, total energy-related CO₂ emissions hit an all-time high of 37.8 gigatonnes, according to the International Energy Agency.

Natural causes of climate change 🔗

Climate change isn’t exclusively human-made. Throughout Earth’s history, natural factors have driven significant climate shifts – from ice ages to warm interglacial periods. However, these natural processes operate on much longer timescales (thousands to millions of years) and cannot explain the rapid warming observed since the mid-20th century.

Volcanic eruptions 🔗

Volcanoes have a complex relationship with climate. When a volcano erupts explosively, it can inject millions of tonnes of sulfur dioxide (SO₂) and ash particles into the stratosphere. These sulfurous aerosols reflect incoming solar radiation, producing a temporary cooling effect that can last one to three years. A well-known example is the 1991 eruption of Mount Pinatubo in the Philippines, which sent around 20 million tonnes of sulfur dioxide into the upper atmosphere and caused global temperatures to drop by roughly 0.5°C for nearly two years.

At the same time, volcanoes release CO₂ into the atmosphere. Over geological timescales, periods of intense volcanic activity at mid-ocean ridges have been associated with elevated atmospheric CO₂ and warmer global temperatures. However, in the present day, volcanic CO₂ emissions are minimal compared to human output. According to the US EPA, human activities currently emit more than 100 times as much CO₂ as all volcanoes combined each year.

Solar variability 🔗

The Sun’s energy output is not perfectly constant. It follows a roughly 11-year sunspot cycle, during which solar radiation fluctuates by small amounts. Historically, changes in solar activity have influenced climate. For instance, the Maunder Minimum – a period of very low sunspot activity from roughly 1645 to 1715 – coincided with the Little Ice Age, a cooler period in Earth’s history.

However, satellite measurements since 1978 show no net increase in the Sun’s energy output, even as global temperatures have risen sharply. Climate models that account only for solar changes – without including rising greenhouse gas concentrations – cannot reproduce the warming trend observed over the past century. This is strong evidence that solar variability plays a minor role in current climate change.

Orbital changes (Milankovitch cycles) 🔗

Over tens of thousands to hundreds of thousands of years, three cyclical changes in Earth’s orbit influence how much solar energy different parts of the planet receive. These are known as Milankovitch cycles and include changes in orbital shape (eccentricity), axial tilt (obliquity), and the wobble of Earth’s axis (precession). These cycles have been closely linked to the timing of past ice ages and warm interglacial periods. But because they operate on such long timescales, they are irrelevant to the rapid warming we’ve seen over the past 150 years.

The role of radiative forcing 🔗

To understand why certain factors warm or cool the climate, scientists use a concept called radiative forcing. It measures how much a particular factor changes the balance between incoming solar energy and outgoing heat radiation at the top of the atmosphere. Radiative forcing is expressed in watts per square metre (W/m²), and it provides a way to compare the climate impact of different drivers side by side.

Positive vs. negative radiative forcing 🔗

A positive radiative forcing means more energy is entering the climate system than leaving it, which causes warming. The accumulation of greenhouse gases is the largest source of positive forcing. A negative radiative forcing means more energy is leaving than entering, which produces cooling. Aerosols – tiny particles from pollution, volcanic eruptions, or natural sources – are the main contributors to negative forcing because they reflect sunlight back into space.

How large is human-caused radiative forcing? 🔗

According to the IPCC’s Sixth Assessment Report, the total human-caused radiative forcing reached approximately 2.72 W/m² in 2019 relative to 1750. This is primarily due to increased concentrations of well-mixed greenhouse gases, partially offset by the cooling effect of aerosols. CO₂ is responsible for the single largest share of this positive forcing, followed by methane, nitrous oxide, and halocarbons. In contrast, natural factors like solar variability and volcanic eruptions have contributed only a very small amount – estimated at between −0.1°C and +0.1°C of total warming since the mid-1800s.

Why radiative forcing matters 🔗

Radiative forcing serves as a kind of scoreboard for climate change. It allows scientists to quantify and compare the warming or cooling influence of each factor – whether it’s CO₂ emissions from power plants, methane from agriculture, sulfate aerosols from industrial pollution, or changes in solar output. By tracking radiative forcing over time, researchers can attribute how much of the observed warming is caused by human activities versus natural processes. The data is clear: the net effect of human activities is overwhelmingly positive (warming), and it far exceeds any natural influences.

Why human impact now dominates 🔗

Natural factors have shaped Earth’s climate for billions of years. But since the Industrial Revolution, human activities have become the dominant force. The evidence is comprehensive and comes from multiple independent sources – ice core records, satellite observations, atmospheric measurements, and climate models.

The IPCC’s latest Synthesis Report states unequivocally that human activities, principally through greenhouse gas emissions, have caused global warming. The planet’s average surface temperature has risen by about 1.3°C since pre-industrial times, and the last decade (2015-2024) is the warmest on record. Current policies, if continued, put the world on track for around 2.7°C of warming by 2100 – well above the Paris Agreement’s target of limiting warming to 1.5°C or at most 2°C.

The distinction between natural and human causes isn’t academic – it’s critical for policy. If warming were primarily solar-driven, it would affect all layers of the atmosphere equally. Instead, scientists observe warming in the lower atmosphere and cooling in the upper atmosphere – a pattern consistent with greenhouse gas accumulation, not solar changes. Climate models that include only natural factors cannot replicate the observed warming. Only when greenhouse gas emissions are added do the models match reality.

What do you think? Given that human-caused greenhouse gas emissions are the dominant driver of current climate change, what do you consider the most impactful change – at the individual, community, or policy level – that could help slow the pace of warming? And how do you think understanding the difference between natural and human causes should shape climate policy decisions?

References

1. https://en.wikipedia.org/wiki/Greenhouse_gas
2. https://www.climate.gov/news-features/understanding-climate/climate-change-atmospheric-carbon-dioxide
3. https://science.nasa.gov/climate-change/causes/
4. https://edgar.jrc.ec.europa.eu/report_2025
5. https://climate.ec.europa.eu/climate-change/causes-climate-change_en
6. https://www.un.org/en/climatechange/science/causes-effects-climate-change
7. https://www.iea.org/reports/global-energy-review-2025/co2-emissions
8. https://science.nasa.gov/earth/earth-observatory/volcanos-and-climate-change/
9. https://www.epa.gov/climatechange-science/causes-climate-change
10. https://www.bgs.ac.uk/discovering-geology/climate-change/what-causes-the-earths-climate-to-change/
11. https://www.ebsco.com/research-starters/earth-and-atmospheric-sciences/radiative-forcing
12. https://en.wikipedia.org/wiki/Radiative_forcing
13. https://www.climate.gov/news-features/understanding-climate/climate-change-global-temperature