The Oxford Dictionary chose ‘climate emergency’ as the 2019 word of the year. In the same year, The Guardian newspaper pledged to only refer to climate change as a ‘climate emergency, crisis or breakdown’. But why is climate change such an urgent issue? We take a look at what’s causing it, how humans are responsible, and why it’s a crisis.
What is climate change?
Climate change is the long-term, large-scale shift in temperature and weather patterns across the planet.
Over the past 4.5 billion years, the Earth’s climate has been continually changing. For example, since the last ice age (approximately 10,000 years ago), the average global temperature has risen by about 3°C to 8°C.
But when you hear the term ‘climate change’ in the news, it’s usually referring to the extremely rapid change to the earth’s climate that has occurred in the last 200 years, due to human activities. According to research carried out by NASA, the planet's average surface temperature has risen by around 0.9°C since the late 19th century, with most of the warming occurring in the past 35 years, and the six warmest years on record taking place since 2014.
These are the kind of changes that would normally happen over hundreds of thousands of years. They are now happening in decades. They cannot be explained by the normal cycles of heating and cooling that the earth naturally undergoes.
Why is climate change happening?
To understand climate change, we first need to understand the greenhouse effect. This is the natural process that warms our planet; without it, it is thought that the Earth’s surface could be as low as -18°C.
The Sun’s energy reaches the Earth’s surface and is reflected toward space as infrared radiation (IR). This is partly absorbed by greenhouse gases (such as carbon dioxide, methane and water vapour) in the atmosphere, raising its temperature. The heated atmosphere in turn radiates IR back toward the Earth’s surface, causing it to rise in temperature also. For a diagram of this process, see the resources at the end of this guide.
However, the vast amount of greenhouse gases that humans have produced in the last 200 years is disrupting this natural process. According to the World Wildlife Fund (WWF), there hasn’t been this level of carbon dioxide (CO2) in the atmosphere for 800,000 years. All these extra tonnes of greenhouse gases mean that more radiation is being absorbed in the atmosphere, and the temperature of the Earth’s surface is rising rapidly.
How do we know?
According to the UN’s Intergovernmental Panel on Climate Change (IPCC), ‘Scientific evidence for warming of the climate system is unequivocal.’ In other words, we definitely know that climate change is happening.
The evidence for this comes from two main sources:
- Modern records. It wasn’t until the mid-19th century that humans started to record global temperatures, and not until 1873 that a standardised method was chosen to ensure accuracy. When meteorologists talk about the hottest or coldest temperatures recorded ‘since records began’, they are referring to this period, lasting from the late 1800s to the present day, in which humans have accurate and real-time data.
- Paleoclimate evidence. This is ancient data about the Earth’s climate and atmosphere from millions of years ago. It often comes from ice cores taken from ice sheets or glaciers. The ice has formed from the incremental buildup of annual layers of snow, so scientists can examine how bubbles of air trapped between layers lower down, which are older, differ from the newer bubbles nearer the surface. Other paleoclimate evidence comes from tree rings, ocean sediments, coral reefs, and layers of sedimentary rocks.
Are humans responsible?
Research published in the peer-reviewed journal Environmental Research Letters found that 97% of scientists agree that humans are driving climate change. This is happening in two main ways:
- Humans emit greenhouse gases into the atmosphere (an estimated 29 gigatonnes per year). This is predominantly due to our reliance on coal, oil, and gas to fuel our lifestyles. When burned, these fossil fuels release CO2 and other gases into the atmosphere.
- Humans have been destroying ‘carbon sinks’ (such as rainforests) which naturally remove CO2 from the atmosphere. This large-scale deforestation is largely to make space for agriculture.
For more details on how human activity is leading to climate change, take a look at our guide The five biggest contributors to greenhouse gas emissions.
Why is it a crisis?
Climate change has already resulted in devastating effects across the globe. In 2016, a paper in Environmental Research Letters showed that five entire pacific islands had been lost due to rising sea levels. According to Save the Children, the Australian bushfires in 2019 burnt nearly 15 million acres of land to the ground, and destroyed approximately 1,400 homes. In East Africa, temperature rises have led to catastrophic droughts and food shortages, resulting in more than 650,000 children under the age of five in Kenya, Somalia and Ethiopia being severely malnourished, according to the United Nations.
These are just some examples, but climate change is having an impact worldwide and, if left unchecked, it will continue to get worse.
To find out how you can help, take a look at our guide Five areas in your life where you can easily reduce your carbon footprint.
- a diagram explaining the greenhouse effect
- evidence of human-driven climate change presented by NASA
- a paper published in Environmental Research Letters confirming the scientific consensus on human-driven climate change
- an interactive infographic that shows the potential impacts of global increases in temperature due to climate change