The average global temperature has risen by more than 1C in the last 140 years – what’s going on and does it matter?
Global warming, climate change, climate crisis, climate breakdown, and climate emergency are all terms which describe a major threat to life as we know it on our planet, but what are people talking about when they use these terms?
Climate and weather
The first important aspect to understanding the world’s climate is distinguishing “climate” from “weather”.
Weather refers only to the changeable short-term atmospheric conditions in a place or area, while climate refers to a much longer pattern of weather behaviour, and can change from season to season.
But there is also the overall climate of the Earth, which is understood through combining the long-term climate records together to build a picture of the trends affecting our planet.
While weather patterns can change over just a few hours, climates usually take hundreds, thousands or even millions of years to change.
However, since the middle of the 20th century, scientists around the world have been warning that climates all around the world, which had been stable for thousands of years, are beginning to change fast and that it is human activity which is largely causing the current changes.
What is happening?
Overall, the world is getting warmer – this is why the process is often known as “global warming”.
The average global temperature on Earth has increased by more than 1C (2F) since 1880. Two-thirds of that warming has occurred since just 1975, at a rate of roughly 0.15-0.20C per decade.
However the world is not uniformly getting hotter. Some areas, such as the Arctic and Antarctic are warming faster than others, and rising average temperatures can have numerous other consequences, which is why the process is better described as “climate change” or “climate breakdown”.
From a human perspective the huge array of negative impacts on us and other species mean it can be thought of as a “climate crisis” or “climate emergency”.
How is the climate changing?
The Earth’s climate is always changing, and before we examine why scientists believe humans are having such a large impact on the climate, it is important to recognise that various natural factors cause major changes to the climate.
- The Earth’s distance to the sun. This increases and decreases over a 100,000-year cycle, during which the Earth’s orbit becomes more elliptical, and then more circular again. Currently the Earth’s orbit is at its most circular, and over the coming millenia, each year during the northern hemisphere’s summer months, the Earth will reach the furthest point from the sun as our planet conducts its 12-month-long orbits, at which point, less solar radiation reaches Earth. It is believed this cycle – known as the Milankovitch Cycle – is a significant factor in causing ice ages.
- The Sun can also produce different levels of solar radiation. It does this over an 11-year time span. In the past, average temperatures have loosely tracked solar activity (within a small range), but since the 1950s, there has been no net increase in solar radiation, indeed, in recent decades, the Sun’s activity has even slightly dropped compared to decades at the end of the 20th century, while average global temperatures have risen markedly.
- The oceans covering 70 per cent of the world’s surface also have a significant impact on climate. This big blue wet thing is continuously exchanging heat, carbon and moisture with the atmosphere, while powerful currents move masses of water around the world, which impact local climates, and clouds form over oceans which are highly reflective and can reflect the sun’s energy back into space. Changes to the heat and carbon storage capacity of the world’s oceans – due to factors including ice cover, sea levels, and carbon dioxide levels – can impact many other climate-affecting processes, such as the oceans’ currents, salinity, temperature and the winds which form over the surface.
- Volcanic eruptions are also natural processes which can have major impacts on the climate. When a powerful volcano erupts, huge amounts of sulphur dioxide, dust and ash are ejected high into the atmosphere, which can reflect sunlight and have a temporary cooling effect which can last some years, though it is not permanent.
Human-driven climate change
Records show that over the last 6,000 years the Earth was on a long slow cooling trajectory, which then suddenly ended during the late Victorian period, around 150 years ago. At this time the human world had already embarked upon a global campaign of industrialisation – a process still underway.
The dawn of industrialisation ignited a planet-wide scramble to excavate exceptionally combustible, energy-rich fuels such as coal, oil and gas, to provide the power required for an endless array of processes including manufacturing, transport, heating and cooling buildings, and domestic use.
This fossil fuel extraction boom is still underway. Though many countries are increasingly switching to renewable energy sources, in 2020, fossil fuels still accounted for 84 per cent of global energy generation, and around the world companies are still planning to keep extracting them.
When fossil fuels are burnt, they emit gases which act to trap the Sun’s heat within the atmosphere, thereby heating up the planet like a greenhouse. This is why they are known as greenhouse gases.
As the process of industrialisation altered societies and produced breakthroughs, particularly in medicine and agriculture, populations of humans have risen sharply around the world.
As well as growing populations demanding greater energy resources – particularly in the richest societies – more people also require more food. As a result, agriculture has had an increasing effect on land use and greenhouse gas emissions – particularly for meat production.
The key greenhouse gases are:
They all come from different processes, have different concentrations in the atmosphere, and have different impacts over different timescales.
Carbon dioxide accounts for about 80 per cent of all greenhouse gases in the atmosphere, but methane, which makes up about 10 per cent, is much more powerful, though over a shorter amount of time.
Nitrous oxide accounts for about 7 per cent, and the fluorinated gases, which are synthetic and very powerful greenhouse gases emitted from a variety of industrial processes, make up the remaining 3 per cent.
Impacts of the climate crisis
A warming world has terrifying consequences. We are already witnessing many of the impacts of climate change, in the form of extreme weather events and an increasing rate of sea level rise, but if the current rate of warming continues, then the worst is still yet to come.
Scientists have warned we will see more frequent and more intense periods of drought; devastating heatwaves which could increase desertification and make areas of the world uninhabitable; more powerful storms; flooding; warming oceans; melting glaciers; retreating sea ice; lack of snow cover; rising sea levels and the destruction of coastal cities where millions live, and biodiversity collapse, risking famines and global food shortages, and therefore increasing risks of conflict and raising the likelihood of mass migrations.
Responding to the multifarious threats posed by the climate crisis is set to be one of our species’ biggest challenges to date.
This is because for many societies, a successful response will involve major recalibrations to people’s fundamental values and expectations, as well as deep changes to the systems and institutions our societies have built themselves on over the last century or more.
But if we are unequal to this recalibration the terrible repercussions will intensify and loom ahead of us like an increasingly sinister spectre.
The one key thing humans must do to slow down our journey into fiery doom is stop producing emissions of greenhouse gases.
The other key thing we must do is repair the damage we have done to the natural world – this will draw the pollutants out of the atmosphere and help slow down the heating process.
Governments around the world are currently only taking small steps to reduce certain emissions and protect and restore a few select ecosystems. These are glimmers of recognition of the problem, but much more needs to be done.