What Is Climate Change? A Really Simple Guide
What Is Climate Change? A Really Simple Guide
What Is Climate Change? A Really Simple Guide
A really simple
guide
While Covid-19 has shaken much of human society, the threat posed by global
warming has not gone away.
There are natural fluctuations in the climate but scientists say temperatures are now
rising faster than at many other times.
This is linked to the greenhouse effect, which describes how the Earth's atmosphere
traps some of the Sun's energy.
Solar energy radiating back to space from the Earth's surface is absorbed by
greenhouse gases and re-emitted in all directions.
This heats both the lower atmosphere and the surface of the planet. Without this effect,
the Earth would be about 30C colder and hostile to life.
Scientists believe we are adding to the natural greenhouse effect, with gases released
from industry and agriculture trapping more energy and increasing the temperature.
Carbon dioxide (CO2), however, persists for much longer. It would take hundreds of
years for a return to pre-industrial levels and only so much can be soaked up by natural
reservoirs such as the oceans.
Most man-made emissions of CO2 come from burning fossil fuels. When carbon-
absorbing forests are cut down and left to rot, or burned, that stored carbon is released,
contributing to global warming.
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Since the Industrial Revolution began in about 1750, CO2 levels have risen more than
30%. The concentration of CO2 in the atmosphere is higher than at any time in at least
800,000 years.
Other greenhouse gases such as methane and nitrous oxide are also released through
human activities but they are less abundant than carbon dioxide.
Across the globe, the average sea level increased by 3.6mm per year between 2005
and 2015.
Most of this change was because water increases in volume as it heats up.
However, melting ice is now thought to be the main reason for rising sea levels. Most
glaciers in temperate regions of the world are retreating.
And satellite records show a dramatic decline in Arctic sea-ice since 1979. The
Greenland Ice Sheet has experienced record melting in recent years.
Satellite data also shows the West Antarctic Ice Sheet is losing mass. A recent study
indicated East Antarctica may also have started to lose mass.
The effects of a changing climate can also be seen in vegetation and land animals.
These include earlier flowering and fruiting times for plants and changes in the
territories of animals.
The WMO says that if the current warming trend continues, temperatures could rise 3-
5C by the end of this century.
Temperature rises of 2C had long been regarded as the gateway to dangerous
warming. More recently, scientists and policymakers have argued that limiting
temperature rises to 1.5C is safer.
But even if we now cut greenhouse-gas emissions dramatically, scientists say the
effects will continue. Large bodies of water and ice can take hundreds of years to
respond to changes in temperature. And it takes CO2 decades to be removed from the
atmosphere.
It could cause fresh water shortages, dramatically alter our ability to produce food, and
increase the number of deaths from floods, storms and heatwaves. This is because
climate change is expected to increase the frequency of extreme weather events -
though linking any single event to global warming is complicated.
Media captionMatt McGrath explains why we should care about climate change
As the world warms, more water evaporates, leading to more moisture in the air. This
means many areas will experience more intense rainfall - and in some places snowfall.
But the risk of drought in inland areas during hot summers will increase. More flooding
is expected from storms and rising sea levels. But there are likely to be very strong
regional variations in these patterns.
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Poorer countries, which are least equipped to deal with rapid change, could suffer the
most.
Plant and animal extinctions are predicted as habitats change faster than species can
adapt. And the World Health Organization (WHO) has warned that the health of millions
could be threatened by increases in malaria, water-borne disease and malnutrition.
Media captionHow temperatures have risen since 1884
As more CO2 is released into the atmosphere, uptake of the gas by the oceans
increases, causing the water to become more acidic. This could pose major problems
for coral reefs.
Global warming will cause further changes that are likely to create further heating. This
includes the release of large quantities of methane as permafrost - frozen soil found
mainly at high latitudes - melts.
Responding to climate change will be one of the biggest challenges we face this
century.