Drivers of Climate Change: Key Factors and Their Impact

Climate change is not driven by a single cause. It results from a combination of natural processes and human activities that alter Earth’s energy balance. Some of these drivers have been shaping the climate for millions of years, while others – particularly those linked to industrialisation – have accelerated dramatically in the last two centuries. Understanding what drives climate change is essential for grasping why global temperatures are rising and what can be done about it.

The greenhouse effect and why it matters 🔗

Earth’s climate depends on a delicate energy balance. Sunlight enters the atmosphere, warms the planet’s surface, and the surface radiates heat back toward space. Greenhouse gases in the atmosphere – including carbon dioxide (CO₂), methane (CH₄), nitrous oxide (N₂O), and water vapour – absorb some of this outgoing heat and re-radiate it, keeping the planet warm enough to sustain life. This is the natural greenhouse effect, and without it, Earth’s average temperature would be well below freezing.

The problem begins when the concentration of these gases rises beyond natural levels. When more greenhouse gases accumulate in the atmosphere, more heat gets trapped, and the planet warms. This enhanced greenhouse effect is the primary mechanism behind modern climate change.

Greenhouse gas accumulation: the core driver 🔗

The ongoing release of greenhouse gases is the single most important factor driving today’s climate change. Each major gas contributes differently to the problem.

Carbon dioxide (CO₂) 🔗

CO₂ is the dominant greenhouse gas in terms of its overall warming impact. According to NOAA’s Annual Greenhouse Gas Index, radiative forcing from long-lived greenhouse gases was 54% greater in 2024 than it was in 1990, with CO₂ being the largest contributor to that increase. Atmospheric CO₂ concentrations reached approximately 422.5 parts per million (ppm) in 2024 – about 52% above pre-industrial levels of roughly 278 ppm.

The primary sources of CO₂ are fossil fuel combustion and land-use changes such as deforestation. According to the U.S. EPA, fossil fuel use is the leading source of CO₂, while deforestation and land degradation release additional stored carbon into the atmosphere. CO₂ is particularly concerning because it persists in the atmosphere for centuries, meaning its warming effect is cumulative over time.

Methane (CH₄) 🔗

Methane is a far more potent greenhouse gas than CO₂ in the short term, though it stays in the atmosphere for a shorter period – roughly 12 years. It accounts for approximately 16% of the total radiative forcing from long-lived greenhouse gases. Major sources of methane include agriculture (especially livestock and rice cultivation), landfills, wetlands, and leaks from oil and gas production. Natural gas itself is composed of 70% to 90% methane, making fossil fuel production and transportation a significant contributor.

Nitrous oxide and fluorinated gases 🔗

Nitrous oxide is released primarily through agricultural activities, particularly the use of synthetic and organic fertilisers, and through fossil fuel combustion. Its atmospheric concentration has risen about 18% over the past century. Fluorinated gases – including hydrofluorocarbons (HFCs) and perfluorocarbons (PFCs) – are entirely industrial in origin and, while present in smaller quantities, have extremely high global warming potential.

Solar and volcanic influences on climate 🔗

Not all climate drivers are human-made. Natural forces – particularly changes in solar output and volcanic eruptions – have influenced Earth’s climate throughout its history. However, their role in the current warming trend is minimal compared to greenhouse gas emissions.

Solar variability 🔗

The Sun’s energy output fluctuates in natural cycles, the most well-known being the roughly 11-year sunspot cycle. During periods of high sunspot activity, the Sun emits slightly more energy; during low activity, it emits less. According to the U.S. EPA, satellite measurements since 1978 show no net increase in the Sun’s energy output, even as global temperatures have continued to rise.

Historically, solar variability did play a role. The Maunder Minimum – a 70-year period from 1645 to 1715 when sunspot activity nearly disappeared – coincided with the coldest phase of the Little Ice Age in Europe. However, the scale of solar influence is small relative to modern greenhouse gas forcing. The warming caused by increased greenhouse gases since 1750 is estimated to be over 270 times greater than any effect from solar variations during the same period.

Volcanic eruptions 🔗

Large volcanic eruptions can temporarily cool the planet. When a volcano erupts explosively, it can inject millions of tonnes of sulfur dioxide into the stratosphere, where it forms sulfate aerosols. These aerosol particles reflect incoming sunlight back to space, reducing the amount of energy reaching Earth’s surface.

The 1991 eruption of Mount Pinatubo in the Philippines is the most well-documented recent example. According to NASA, the eruption sent an estimated 20 million tons of sulfur dioxide into the stratosphere, and the resulting aerosol cloud circled the globe within three weeks. Surface temperatures in the Northern Hemisphere dropped by up to 0.5-0.6°C, and the cooling effect lasted about two to three years.

However, volcanic cooling is inherently short-lived. Once the aerosols settle out of the stratosphere, temperatures return to pre-eruption levels. Importantly, while volcanoes do release CO₂, human activities emit more than 100 times as much CO₂ annually as all the world’s volcanoes combined. So, volcanic eruptions are disruptive in the short term but not a driver of the long-term warming trend we see today.

Human-induced radiative forcing: the dominant factor 🔗

Radiative forcing measures the change in Earth’s energy balance – specifically, the difference between incoming solar energy and outgoing heat. When the forcing is positive, it means the planet is absorbing more energy than it’s releasing, which causes warming. Human activities have pushed this balance significantly into positive territory.

What is radiative forcing? 🔗

Scientists use 1750 – the approximate start of the Industrial Revolution – as a baseline year for measuring radiative forcing. Any change from that baseline, caused by factors like rising greenhouse gas levels or increased aerosol concentrations, is expressed in watts per square metre (W/m²). As the NOAA Climate.gov explains, since 1750, human-caused climate forcings have been increasing, and their combined effect now dominates all natural climate drivers.

The most recent data from the Indicators of Global Climate Change 2024 report, published in Earth System Science Data, estimates total anthropogenic effective radiative forcing in 2024 at 2.97 W/m², which is 9% higher than the 2019 value cited in the last IPCC assessment. This increase reflects both growing greenhouse gas concentrations and declining aerosol emissions (since aerosols from air pollution had been partially masking the warming effect of greenhouse gases).

Fossil fuel combustion 🔗

Burning coal, oil, and natural gas is the largest source of human-caused greenhouse gas emissions. According to the United Nations, fossil fuels account for roughly 68% of total global greenhouse gas emissions and nearly 90% of all CO₂ emissions. The Global Carbon Budget for 2024 projected total CO₂ emissions at 41.6 billion tonnes, with fossil fuel emissions alone reaching 37.4 billion tonnes – an all-time high with no sign of a global peak yet reached.

The energy sector is the biggest emitter. Electricity and heat generation, transportation, and manufacturing collectively produce the majority of fossil fuel emissions. Road transportation alone accounts for over 12% of global emissions, while residential energy use contributes another 12.5%, according to analysis by the World Resources Institute.

Deforestation and land-use change 🔗

Forests serve as natural carbon sinks, absorbing CO₂ from the atmosphere through photosynthesis and storing it in their biomass. When forests are cleared – for agriculture, development, or logging – the stored carbon is released back into the atmosphere. Deforestation and other land-use changes are responsible for roughly one-third of global greenhouse gas emissions when combined with agriculture, according to the United Nations.

In 2024, emissions from land-use change (primarily deforestation) were projected at 4.2 billion tonnes of CO₂. Drought conditions linked to the 2023-2024 El Niño event worsened these emissions by intensifying deforestation fires, particularly in tropical regions like Brazil. While reforestation efforts do offset some of these losses – about half of permanent deforestation emissions, by current estimates – the overall trajectory remains a net addition of CO₂ to the atmosphere.

The declining aerosol mask 🔗

An often-overlooked factor in radiative forcing is the role of aerosols from air pollution. Sulfate aerosols from industrial processes and fossil fuel combustion reflect sunlight and have a cooling effect on the climate. Paradoxically, as countries clean up air pollution – a welcome development for public health – the cooling mask these aerosols provided is being removed, allowing more of the underlying greenhouse gas warming to come through. The 2024 IGCC report confirmed that cooling aerosol emissions continue to decline, contributing to the rise in total effective radiative forcing.

Natural vs. human drivers: putting it in perspective 🔗

The IPCC’s Sixth Assessment Report concluded unequivocally that the increase of CO₂, methane, and nitrous oxide in the atmosphere since the industrial era is the result of human activities, and that human influence is the principal driver of observed changes across the atmosphere, ocean, cryosphere, and biosphere.

Between 2015 and 2024, global temperatures averaged 1.24°C above pre-industrial levels. Of this, 1.22°C was attributed to human activities – meaning essentially all of the observed warming was human-caused. Natural drivers like solar variability and volcanic eruptions can cause short-term fluctuations, but they cannot explain the sustained, long-term warming trend of the past several decades.

Climate models confirm this picture. When scientists run simulations using only natural forcings – solar changes, volcanic eruptions, and internal variability – the models cannot reproduce the warming observed since the mid-20th century. Only when human-caused emissions are included do the models match what has actually been measured.

Why understanding these drivers matters 🔗

Identifying the key drivers of climate change is not just an academic exercise. It directly informs climate policy and mitigation strategies. If the dominant driver is greenhouse gas accumulation from fossil fuels and deforestation, the solution priorities become clear: transition to renewable energy, protect and restore forests, reduce methane emissions from agriculture and fossil fuel infrastructure, and improve energy efficiency across all sectors.

The data also underscores the urgency. At current emission rates, the remaining carbon budget for limiting global warming to 1.5°C is estimated to be exhausted within approximately six years. The longer emissions continue to rise, the steeper the cuts required in the future – and the greater the risk of irreversible climate impacts.

What do you think? Given that human activities are responsible for virtually all observed warming, how should individuals and governments prioritise their climate actions? And with natural carbon sinks like forests under increasing stress from climate change itself, how can we ensure these ecosystems continue to help absorb the CO₂ we emit?

References

1. https://climate.mit.edu/explainers/radiative-forcing
2. https://gml.noaa.gov/aggi/aggi.html
3. https://www.epa.gov/ghgemissions/global-greenhouse-gas-overview
4. https://science.nasa.gov/climate-change/causes/
5. https://www.epa.gov/climatechange-science/causes-climate-change
6. https://science.nasa.gov/earth/earth-observatory/volcanos-and-climate-change/
7. https://scied.ucar.edu/learning-zone/how-climate-works/how-volcanoes-influence-climate
8. https://www.climate.gov/maps-data/climate-data-primer/predicting-climate/climate-forcing
9. https://www.un.org/en/climatechange/science/causes-effects-climate-change
10. https://www.wri.org/insights/4-charts-explain-greenhouse-gas-emissions-countries-and-sectors