What is Climate Change? Definitions and Perspectives

Climate change is one of the most discussed environmental topics of our time – but what does it actually mean? Depending on who you ask, the definition shifts. Some define it broadly as any long-term shift in weather patterns, while others narrow it down to changes caused specifically by human activity. These distinctions matter more than you might think, because how we define climate change shapes the policies we create and the actions we take.

What does climate change actually mean? 🔗

At its core, climate change refers to significant, lasting alterations in the statistical distribution of weather patterns over periods ranging from decades to millions of years. This can include changes in average temperature, rainfall, wind patterns, and the frequency of extreme weather events.

But here’s where it gets interesting: two of the world’s most influential bodies on climate – the Intergovernmental Panel on Climate Change (IPCC) and the United Nations Framework Convention on Climate Change (UNFCCC) – define the term differently. And that difference has real consequences for global policy.

The IPCC definition 🔗

The IPCC, established in 1988 by the World Meteorological Organization (WMO) and the United Nations Environment Programme (UNEP), is the leading scientific body assessing climate change globally. Its reports are considered the most comprehensive and authoritative scientific assessments available on the subject.

The IPCC defines climate change as any change in the state of the climate that can be identified – through statistical tests – by changes in the mean or variability of its properties, and that persists for extended periods, typically decades or longer. Crucially, this definition covers changes driven by both natural processes and human activities. So whether the change comes from volcanic eruptions, shifts in solar radiation, or fossil fuel burning, the IPCC considers it all climate change.

The UNFCCC definition 🔗

The UNFCCC takes a narrower approach. Under Article 1 of the Convention, climate change is defined as a shift in climate attributed directly or indirectly to human activity that alters the composition of the global atmosphere – and that is separate from natural climate variability observed over comparable time periods.

In other words, the UNFCCC focuses exclusively on human-caused changes. Natural variability, while acknowledged, is treated as a separate phenomenon. This distinction is deliberate: the Convention was designed to hold governments accountable for anthropogenic emissions, so its definition had to zero in on what humans are doing to the atmosphere.

Natural climate variability: what changes without us 🔗

Earth’s climate has never been static. Long before humans industrialised, the planet experienced dramatic shifts – ice ages, warm interglacial periods, and everything in between. These changes are driven by natural factors that influence how much energy Earth receives, retains, and reflects.

Earth’s orbital changes 🔗

Small variations in Earth’s orbit around the Sun – known as Milankovitch cycles – have been the primary drivers of ice age cycles over the past several hundred thousand years. According to the U.S. Environmental Protection Agency, the amount of summer sunlight reaching the Northern Hemisphere, driven by orbital shifts, appears to be the main cause of past ice age cycles. At the coldest point of the last glacial period, global temperatures were roughly 11°F (about 6°C) cooler than today.

Volcanic activity 🔗

Volcanic eruptions can have short-term cooling effects on climate. Explosive eruptions inject particles like sulphur dioxide (SO₂) into the upper atmosphere, where they reflect sunlight and can temporarily cool the Earth’s surface for several years. However, these particles don’t linger long enough to drive lasting climate change. It’s also worth noting that human activities emit over 100 times more CO₂ than volcanoes annually.

Solar output variations 🔗

The Sun follows a natural 11-year cycle of slight variations in energy output. While this can modestly influence Earth’s climate, satellite measurements taken since 1978 show no net increase in solar energy reaching Earth – even as global surface temperatures have risen significantly. As Environment and Climate Change Canada notes, since the Industrial Revolution, the warming effect of added greenhouse gases has been more than 50 times greater than any change in the Sun’s output.

The human factor: how we accelerated the change 🔗

While natural processes explain climate shifts over geological timescales, they cannot account for the rapid warming we’ve seen since the mid-1800s. The current warming trend is fundamentally different – in both speed and cause – from anything in Earth’s recent past.

The Industrial Revolution as a turning point 🔗

The burning of coal, oil, and natural gas that began with the Industrial Revolution has increased atmospheric carbon dioxide concentrations by about 50% compared to pre-industrial levels. According to NASA, scientists demonstrated the heat-trapping nature of CO₂ and other gases as far back as the mid-19th century. What followed – decades of accelerating fossil fuel use – turned a scientific finding into a planetary-scale problem.

NOAA data shows that atmospheric CO₂ reached a record average of 422.7 parts per million (ppm) in 2024, with the annual rate of increase running roughly 100 times faster than natural increases seen at the end of the last ice age. Before industrialisation, CO₂ levels had remained between 170 and 300 ppm for at least 800,000 years.

Key greenhouse gases driving modern climate change 🔗

Carbon dioxide gets the most attention – and rightly so – because it accounts for the majority of human-caused warming and persists in the atmosphere for centuries. But it isn’t alone:

Methane (CH₄) is released through livestock digestion, rice farming, landfills, and leaks from fossil fuel production. Natural gas itself is 70-90% methane. Nitrous oxide (N₂O) comes primarily from agricultural fertiliser use and fossil fuel combustion, and has increased by about 18% over the last century. Fluorinated gases like hydrofluorocarbons (HFCs) are entirely industrial in origin and, while present in smaller quantities, are extremely potent at trapping heat.

As the Natural Resources Defense Council points out, atmospheric concentrations of CO₂, methane, and nitrous oxide are currently at their highest levels in at least 800,000 years.

Deforestation and land use change 🔗

It’s not just about what we put into the air – it’s also about what we remove from the ground. Forests, wetlands, and soils act as natural carbon sinks, absorbing CO₂ from the atmosphere. Large-scale clearing of forests for agriculture and development has reduced the planet’s capacity to absorb carbon, further accelerating the accumulation of greenhouse gases in the atmosphere.

Why natural causes alone can’t explain what’s happening now 🔗

Some may wonder: if the climate has changed naturally before, how do we know humans are the cause this time? The evidence is extensive and comes from multiple independent lines of research.

According to NASA’s climate science division, the current warming trend is proceeding roughly 10 times faster than the average rate of warming after an ice age, and CO₂ is rising about 250 times faster than it did from natural sources during that same period. Additionally, if the Sun were causing the current warming, scientists would expect all layers of the atmosphere to warm – but instead, the upper atmosphere is cooling while the lower atmosphere warms, which is the signature pattern of greenhouse gas-driven warming.

The scientific consensus is firm. The IPCC’s Sixth Assessment Report, drawing on the work of hundreds of scientists and thousands of peer-reviewed studies, confirmed that human influence on the climate system is unequivocal.

Why definitions matter for policy and action 🔗

At first glance, the difference between the IPCC and UNFCCC definitions might seem like academic hair-splitting. But it has serious practical implications.

Accountability and responsibility 🔗

The UNFCCC’s human-focused definition was crafted deliberately. By separating human-caused changes from natural variability, the Convention created a framework in which nations can be held responsible for their emissions. This distinction forms the legal backbone of international agreements like the Kyoto Protocol (1997) and the Paris Agreement (2015).

Under the Paris Agreement, countries commit to limiting global temperature rise to well below 2°C above pre-industrial levels, with efforts to keep it to 1.5°C. That target only makes sense if we’re measuring the warming attributable to human actions – which is precisely what the UNFCCC definition supports.

Scientific scope vs. policy scope 🔗

The IPCC’s broader definition serves a different purpose. By including both natural and human-caused changes, the IPCC can assess the full picture of how the climate system works. This helps scientists understand how natural variability and human-driven change interact – critical knowledge for accurate climate modelling and future projections.

In short, the IPCC definition is built for understanding, while the UNFCCC definition is built for action. Neither is wrong; they serve different functions within the global effort to address climate change.

The policy implications are real 🔗

Consider this: if a government argues that recent warming is primarily natural, it has less incentive to cut emissions. The UNFCCC definition closes that loophole by focusing squarely on human-caused changes. Meanwhile, the IPCC’s comprehensive approach ensures that policy decisions are informed by the best available science on all climate drivers.

The interplay between these two definitions has shaped landmark agreements. As noted by the World Resources Institute, the IPCC’s Sixth Assessment Synthesis Report drew on the work of over 780 scientists and served as a crucial input for international climate negotiations. IPCC findings don’t dictate policy, but they provide the evidence base that frameworks like the UNFCCC translate into binding commitments.

The current state of climate change 🔗

Regardless of which definition you use, the data points in the same direction. Global temperatures have already risen by approximately 1.1°C above pre-industrial levels, and the consequences are visible across every region of the world – rising sea levels, more frequent and intense extreme weather events, shrinking ice sheets, and disrupted ecosystems.

The IPCC’s latest synthesis report warns that every additional fraction of a degree matters. Each 0.5°C of further warming would bring clearly discernible increases in heat extremes, heavy rainfall, and regional droughts. The window for meaningful action is narrowing, but the report also emphasises that limiting warming to 1.5°C – while increasingly difficult – remains possible with immediate, deep reductions in greenhouse gas emissions across all sectors.

Understanding the definition of climate change isn’t just an academic exercise. It’s the foundation for understanding why the problem exists, who is responsible, and what we can do about it.

What do you think? Does it matter whether we define climate change broadly (including natural causes) or narrowly (only human-caused changes)? How do you think these definitions should influence the way governments set their emission targets?

References

1. https://www.ipcc.ch/
2. https://unfccc.int/resource/docs/convkp/conveng.pdf
3. https://www.epa.gov/climatechange-science/causes-climate-change
4. https://www.canada.ca/en/environment-climate-change/services/climate-change/causes.html
5. https://science.nasa.gov/climate-change/causes/
6. https://www.climate.gov/news-features/understanding-climate/climate-change-atmospheric-carbon-dioxide
7. https://www.nrdc.org/stories/what-are-causes-climate-change
8. https://science.nasa.gov/climate-change/evidence/
9. https://en.wikipedia.org/wiki/United_Nations_Framework_Convention_on_Climate_Change
10. https://www.wri.org/insights/2023-ipcc-ar6-synthesis-report-climate-change-findings