“It is unequivocal that human influence has warmed the atmosphere, oceans and land” - Intergovernmental Panel on Climate Change, 6th Assessment Report, 2021
Natural climate variability
Over the course of the Earth’s 4.5-billion-year history, our climate on varying timescales has been primarily controlled by natural factors. This is because humans have only existed on Earth for the latter 0.007% of its history. Examples of natural factors include changes in volcanic activity and the Earth’s orbit around the sun; the latter influences the distribution of the sun’s energy across the Earth’s surface and has been the main driver of a series of cooler (glacials) and warmer climates (interglacials) that have occurred on cycles of ~100,000 years.
Human-induced climate change
The last cold glacial period ended ~20,000 years ago, after which we have remained in a relatively stable and warm interglacial climate. However, since the 1800s, the climate has been warming at an unprecedented rate, and the sheer speed of warming cannot be explained by natural forces.
The 6th Assessment Report from the Intergovernmental Panel on Climate Change (IPCC) makes clear that global warming has been “unequivocally” caused by human activities, primarily from the burning of fossil fuels such as oil, coal and gas. These fuels are typically used to produce our energy needs, such as to power engines in cars or produce electricity that supply our homes.
However, an unfortunate by-product of our energy production is the significant release of carbon dioxide (CO2) to the atmosphere (often referred to as CO2 emissions). This emitted carbon would have otherwise been stored deep underground for millions of years.
CO2 emissions and the greenhouse effect
Since the beginning of the Industrial Revolution, the CO2 concentration in the Earth’s atmosphere has increased by 50% (280 ppm to 420 ppm). Like all other greenhouse gases, CO2 absorbs the sun’s energy and forms a “warming blanket” over the Earth. This phenomenon is known as the “greenhouse effect”, and the higher the abundance of these gases in the atmosphere, the warmer our climate becomes.
Scientists estimate that the amount of CO2 in the atmosphere is now higher than at any time in the last 2 million years, and human influence has warmed the climate at a rate that is unprecedented in at least the last 2000 years. As a result, the global average temperature has warmed by ~1 °C since the beginning of industrialisation. This warming may sound trivial, but changes in extreme climate events, such as heatwaves, flooding, droughts, and tropical cyclones, are already being felt across many regions of the globe, and many of the impacts are considered irreversible and increasing.
UK greenhouse gas emissions
According to provisional data, Britain emitted 424.5 million tonnes of carbon dioxide equivalent in 2021, which was 4.7% higher than in 2020 but 5.2% lower than in 2019 - the most recent pre-pandemic year. The UK has decreased its emissions since the mid-2000s due to a shift away from coal-fired power stations. As a result, greenhouse gas emissions are now 47.3% lower than they were in 1990.
However, many other sectors have made little progress in cleaning up their act. The transport sector was the main source of CO2 emissions in the UK in 2021 (31% of the total emissions), having exceeded the energy sector as the top emitter since 2016. Emissions from the energy sector have continued to decrease since the mid-2000s, driven mainly by the growth in the amount of energy produced from renewable sources, such as wind and solar.
Despite being the largest emitting sector, emissions from transport fell slightly (1.8%) for the second year in a row in 2019, driven mainly by improvements in fuel efficiency and reduced petrol consumption. The Covid-19 lockdowns significantly reduced the number of vehicles on the road in 2020, causing a further 19% decrease in transport emissions from the previous year.
However, as predicted, transport emissions recovered swiftly as we emerged from the pandemic, resulting in the highest increase in CO2 emissions (+10%) of all sectors from 2020 to 2021.
UK carbon solution
The recent IPCC report states that a global warming of 2°C above preindustrial levels will be exceeded before the end of the century unless we significantly reduce CO2 emissions in the coming decades.
Passenger cars are the largest CO2 contributors in Britain’s transport sector. This means that we can individually have a significant impact on the UK’s transport emissions, just by changing the way we travel.
For example, choosing to walk or cycle instead of driving can both reduce pollution and contribute to an active and healthy lifestyle. Using public transport can also minimise the number of vehicles on the road and reduce traffic congestion. And finally, studies suggest that switching from a petrol to an electric car can reduce your vehicular CO2 emissions by up to 30% throughout its lifetime. This figure will only increase as we continue to source more electricity from renewable sources.
The challenge of tackling the climate crisis can seem overwhelming. Scientists stress that a climate catastrophe can be avoided if we stick to our global commitments of cutting emissions by half by 2030 and reaching net zero emissions by 2050, but time is ticking. We can all take steps to reduce our carbon footprint by shifting our behaviours towards ones that benefit the planet.
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