What is climate change? A really simple guide
While Covid-19 has shaken much of human society, the threat posed by global warming has not gone away.
Human activities have increased carbon dioxide (CO2) emissions, driving up temperatures. Extreme weather and melting polar ice are among the possible effects.
What is climate change?
Climate is the average weather in a place over many years. Climate change is a shift in those average conditions.
The Earth is now in a period of rapid climate change, with global temperatures rising because of human activities, such as the burning of coal, oil and gas.
What is the impact?
People: Climate change will transform the way people live, causing water shortages and making it harder to produce food.
Some regions could become dangerously hot and others uninhabitable because of rising sea levels.
Extreme weather events - such as heatwaves, downpours and storms - will become more frequent and intense, threatening lives and livelihoods.
People in poorer countries, which are least able to adapt, will suffer most.
Environment: Polar ice and glaciers are melting fast, contributing to rising seas.
As permafrost - frozen ground - melts in Siberia and other regions, methane - another greenhouse gas - will be released into the atmosphere, worsening climate change.
The weather conditions needed for wildfires are becoming more likely and low-lying coastal areas are threatened with flooding by rising seas.
Nature: As their habitats change, some species will be able to move to new locations.
But climate change is happening so rapidly many are likely to become extinct.
Polar bears are at risk of disappearing as the ice they rely on melts away.
Atlantic salmon could be devastated as the river waters in which they breed warm up.
Tropical coral reefs may disappear as oceans absorb more CO2 and become more acidic.
What are the causes?
There have always been natural variations in the climate.
But scientists say temperatures are now rising at an alarming rate - and it's caused by people.
The world is about 1.2C warmer than before people started using oil, gas and coal to power factories and transport and heat homes.
The greenhouse gases released by burning fossil fuels trap the Sun's energy, pushing up temperatures.
CO2 levels in the atmosphere have risen by about 50% since the 19th Century and by 12% in the past two decades.
Fossil fuels release particular types of carbon and the proportion of these has increased.
Another source of greenhouse gases is deforestation.
When trees are burned or chopped down, the carbon they normally store is released
What will happen in the future?
Scientists have set a temperature increase of 1.5C as the "safe" limit for global warming.
If temperatures go higher, damaging changes to the natural environment will probably transform humans' way of life.
Many scientists believe this will happen and predict temperature rises of 3C or more by the end of the century.
The effects will vary depending on where people live:
The UK will be vulnerable to flooding caused by extreme rainfall
Low-lying island nations in areas such as the Pacific region could disappear under rising seas
Many African nations are likely to suffer drought and food shortages
In North America, worsening drought conditions are likely to hit the western US, while other areas will probably see increased rainfall and more intense storms
Australia is likely to suffer extremes of heat and drought, raising the risk of fires
What are governments doing?
Many countries are adopting targets that would reduce their greenhouse-gas emissions to "net zero" by about the middle of this century.
This means any emissions would be balanced out by absorbing an equivalent amount - through planting trees, for example.
The hope is this will stave off the most dangerous effects of climate change, by arresting the rapid rise in temperature.
What are scientists doing?
Scientists are studying the changes caused by rising temperatures.
Their understanding of the climate is increasing all the time.
For example, they have now been able to make a link between climate change and single weather events such as extreme rainfall and heatwaves.
The hope is improved computing power could help scientists better predict these extreme events in future.
What can individuals do?
Scientists say people can:
reduce their reliance on cars by taking public transport or cycling
insulate their homes
take fewer flights
eat less meat and dairy
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