Human activities are causing world temperatures to rise, posing serious threats to people and nature.
Things are likely to worsen in the coming decades, but scientists argue urgent action can still limit the worst effects of climate change.
What is climate change?
Climate change is the long-term shift in the Earth’s average temperatures and weather conditions.
The world has been warming up quickly over the past 100 years or so. As a result, weather patterns are changing.
Since the 1980s, each decade has been warmer than the previous one, the UK Met Office says.
In addition, the world’s 11 warmest years on record have all happened since 2015, according to the World Meteorological Organization (WMO).
The year 2024 was Earth’s hottest ever recorded, with climate change mainly responsible for the high temperatures.
It was also the first calendar year to surpass 1.5C of warming compared to “pre-industrial” levels of the late 1800s, according to the European Copernicus climate service.
Temperatures remained high in 2025, despite a slight cooling from a natural weather pattern called La Niña.
How are humans causing climate change?
The climate has changed naturally throughout the Earth’s history.
But natural causes cannot explain the particularly rapid warming seen over the last century, according to the UN’s climate body, the Intergovernmental Panel on Climate Change (IPCC).
This has been without doubt caused by human activities, in particular the widespread use of fossil fuels – coal, oil and gas – in homes, factories and transport systems.
When fossil fuels burn, they release greenhouse gases – mostly carbon dioxide (CO2). This CO2 acts like a blanket, trapping extra energy in the atmosphere near the Earth’s surface. This causes the planet to heat up.
Since the start of the Industrial Revolution – when humans started burning large amounts of fossil fuels – the amount of CO2 in the atmosphere has risen by more than 50%, far above levels seen in the Earth’s recent history.
The CO2 released from burning fossil fuels has a distinctive chemical fingerprint. This matches the type of CO2 increasingly found in the atmosphere.
What effects of climate change have already been seen?
Climate change has already had a huge effect, including: more frequent and intense extreme weather, such as heatwaves and heavy rainfall, rapid melting of glaciers and ice sheets, contributing to sea-level rise, the shrinking of Arctic sea-ice, warmer oceans, which can fuel more intense storms and harm sea life.
Why does 1.5C matter and how will future climate change affect the world?
The more the world warms, the worse the impacts of climate change become.
Nearly 200 countries have pledged to try to limit global warming to 1.5C above pre-industrial levels, as part of the 2015 Paris climate agreement.
That target is generally understood to relate to an average annual increase of 1.5C recorded over 20 years, rather than a one-off rise captured in an individual 12-month period.
Long-term warming of 1.5C would still bring serious consequences for many populations.
But a very large body of scientific evidence shows that warming of 2C or more would bring far greater impacts, on top of those felt at 1.5C, the IPCC says.
The call to restrict temperature rise to 1.5C was partly designed to avoid crossing so-called “tipping points”.
It is not clear exactly where they sit, but once these thresholds are passed, changes could accelerate and become irreversible.
These could include the collapse of the Greenland Ice Sheet, warm Atlantic Ocean currents or further loss of the Amazon rainforest. These changes are already having serious consequences for people and economies around the world. (BBC)
