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It's all a question of averages
Climate has been called the long‐term average weather conditions of a place.
That's because the global climate has been pretty stable for most of human history. Weather conditions in most places stayed more or less the same over the centuries. For example, about the same amount of rain fell each year and there were similar temperatures.
But in the last hundred years or so we've seen changes in long-term average weather conditions in many place around the world caused by human activities.
When average weather changes over the course of several decades, scientists usually take it as a sign that change is permanent. That's what we call climate change.
Let it snow!
An example is the average amount of snow in the northern hemisphere each spring.
Over the last 50 years, spring snow cover has been disappearing earlier in the year than it did in the past.
Between 1967 and 2022 in the northern hemisphere:
- April snow cover reduced by 1.32% per decade
- May snow cover reduced by 4.1% per decade
- June snow cover reduced by 12.95% per decade
So, the clear trend is that spring snow cover is reducing. A time traveller from 100 years ago would notice the reduction in average amounts of snow compared with the 1920s. That’s an example of climate change.
Next section: What causes climate change?
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These 'climate stripes' from the University of Reading are a great way to see how our climate is hotting up. The stripes represent the average annual global temperature since 1850.
They use reds for hotter years and blues for cooler years. The red stripes on the right represent recent decades. This clearly shows how temperatures have risen dramatically due to human-caused climate change.
The Met Office publishes information about global warming. You can find information about the Paris Agreement, which aims to limit further temperature rises to 1.5°C.
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