Earth's climate has always changed — ice ages, warm periods, mass extinctions driven by volcanic eruptions. What's different now is the speed, the cause, and the scale.
The greenhouse effect
Earth is kept warm by the greenhouse effect. Sunlight passes through the atmosphere and warms the surface. The surface radiates heat back upward as infrared radiation. Greenhouse gases — mainly water vapour, carbon dioxide, and methane — absorb some of this outgoing heat and radiate it back towards Earth, keeping it warmer than it would otherwise be. Without any greenhouse effect, Earth's average temperature would be around −18°C instead of the current +15°C. The greenhouse effect is not a problem; it's essential for life.
The problem is too much of it.
Imagine Earth's atmosphere is a duvet on a bed. A thin duvet keeps you comfortably warm on a cold night. A thicker duvet keeps you warmer still. Keep adding duvets and you start to overheat. Since the Industrial Revolution, humans have been adding CO₂ to the atmosphere at an unprecedented rate — thickening the duvet. The bed is warming, and the consequences of overheating ripple through everything the bed is connected to.
Where is the extra CO₂ coming from?
Primarily from burning fossil fuels — coal, oil, and natural gas — which releases CO₂ that was locked underground for millions of years. Deforestation releases CO₂ stored in trees. Agriculture produces methane (from livestock) and nitrous oxide (from fertilisers), both powerful greenhouse gases. Since 1750, atmospheric CO₂ concentration has risen from about 280 parts per million to over 420ppm — higher than at any point in the past 800,000 years, based on ice core evidence.
Why does 1.2°C matter?
Global averages hide local extremes. A 1.2°C rise in average temperature means much more frequent heatwaves, stronger storms, faster-melting ice, rising sea levels, and disrupted rainfall patterns that affect agriculture. The concern is feedback loops: melting Arctic ice (which reflects sunlight) exposes darker ocean (which absorbs it), causing more warming; melting permafrost releases stored methane, causing more warming. Each degree of additional warming makes subsequent degrees more likely and faster-arriving.
Earth's climate has always changed. There have been ice ages and warm periods. There have been big extinctions caused by volcanoes. What's different now is how fast it's happening. It's also different because of what's causing it and how big it is.
The greenhouse effect
Earth is kept warm by something called the greenhouse effect. Sunlight comes through the air and warms the ground. The ground sends heat back up into the air. Special gases in the air catch some of this heat. These gases are mainly water vapour, carbon dioxide, and methane. They send the heat back down to Earth. This keeps Earth warmer than it would be without these gases. Without any greenhouse effect, Earth would be about −18°C instead of +15°C. The greenhouse effect is not bad - we need it to live.
The problem is having too much of it.
Think of Earth's air like a blanket on your bed. A thin blanket keeps you nice and warm on a cold night. A thicker blanket keeps you even warmer. Keep adding more blankets and you get too hot. Since factories started being built, people have been adding CO₂ to the air very quickly. This makes the blanket thicker. The Earth is getting warmer. This causes problems for everything connected to Earth.
Where is the extra CO₂ coming from?
Most of it comes from burning fossil fuels. These are coal, oil, and natural gas. When we burn them, they release CO₂. This CO₂ was trapped underground for millions of years. Cutting down forests also releases CO₂ that was stored in trees. Farming makes methane gas from cows and other animals. Fertilisers make nitrous oxide gas. Both of these gases are very powerful at trapping heat. Since 1750, the amount of CO₂ in the air has gone up a lot. It went from about 280 parts per million to over 420 parts per million. This is higher than it has been for 800,000 years. We know this from studying old ice.
Why does 1.2°C matter?
When we say the Earth is 1.2°C warmer, this is the average. Some places get much hotter than this. This small change means we get heatwaves much more often. Storms become stronger. Ice melts faster. Sea levels go up. Rain patterns change, which affects growing food. The worry is that warming causes more warming. When Arctic ice melts, it shows dark ocean underneath. Dark water soaks up more heat than white ice. This makes things even warmer. When frozen ground melts, it releases methane gas. This also makes things warmer. Each degree of warming makes the next degree happen faster.