Global warming vs Climate change

The terms "climate change" and "global warming" are heavily charged. Yet, they're often misunderstood and misused, which only adds to the confusion over the actual issues they encompass. Here, we dig into what they mean today and how they're impacting our planet right now.

What is climate change?

"Climate change" is the name given to the process by which weather conditions alter to such an extent that both the climate and the environment become significantly transformed.

The change, which normally takes place over a very long time period, typically produces colder or warmer conditions, and these have far-reaching impacts on many aspects of life, including flora and fauna.

There are lots of naturally occurring reasons why climate change happens, from long-term changes in the Earth's orbit around the sun to relatively short-term shifts, caused by, for example, periods of low solar activity, massive volcanic eruptions and fluctuations in the oceans' currents.

Natural cycles

For hundreds of thousands of years, Earth's climate has shifted in slow, predictable cycles, and one of the most significant relates to the planet's orbit around the sun. As it circles the sun, its trajectory subtly stretches and tilts. These shifts, known as Milankovitch cycles, after Milutin Milankovitch, the scientist who first identified them, alter the amount of sunlight that reaches Earth.

Over time, that small difference is enough to tip the planet into icy glacial ages or warmer interglacial periods. Over the past 740,000 years, there have been eight such glacial cycles, part of a pattern that has shaped landscapes and ecosystems for millions of years.

The Earth is currently in an interglacial period following the last ice age, which peaked around 20,000 to 26,000 years ago. Then, ice sheets covered much of North America and northern Europe, and sea levels were at least 100 metres lower than they are today. According to the geological record, the next glacial cycle is likely to begin in around 10,000 to 11,000 years.

It's important to note that the climate changes we're discussing here are all natural ones that come around in cycles over very long periods of time. You may not realise it, but we are in a cycle now. However, due to the time frames involved, the process of natural change is barely perceptible.

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What is global warming?

Another term often used is "global warming", which is different to climate change. However, the two terms are often conflated and used interchangeably, although technically they have different meanings.

We've examined naturally occurring climate change, which is happening right now. In addition, today, we are experiencing (and have been since the mid-19th century), a small but steady increase in surface temperature that is almost entirely due to human activities. This is what we call "global warming".

It's a very real consequence that we need to know about and should be concerned about. Not only because it is an entirely new phenomenon, but because the rate at which temperatures are changing, though relatively small, is unprecedented.

Furthermore, rising temperatures have knock-on effects that go beyond warmer weather. They are leading to more frequent extreme weather events, rising sea levels and changing ecosystems.

Why are temperatures rising?

Earth has always cycled between colder ice ages and warmer intervals, but today's rapid warming has a different driver: us. Human activity, chiefly the burning of coal, oil and gas, has filled the atmosphere with what are known as 'greenhouse gases', such as carbon dioxide, methane and nitrous oxide.

These gases act like the glass of a greenhouse. Normally, about 30% of the solar radiation that warms the land and oceans is released back into space through a process known as 'outgoing longwave radiation'.

This is a crucial part of the mechanism that governs our planet's climate. So long as the amount of energy arriving from the sun is equal, on average, to the amount lost back into space, then the temperature of the Earth remains stable.

The problem is that outgoing longwave radiation is being negatively affected by the presence of greenhouse gases in the atmosphere, which trap part of that heat and send it back towards the surface. As the levels of these gases rise, less heat escapes and the planet warms.

We've understood the basics for a long time. In the mid-19th century, scientists, including John Tyndall and Svante Arrhenius, warned that extra carbon dioxide (CO2) could warm the Earth.

The first real evidence that this warming was already underway came in 1938, when British engineer Guy Callendar showed temperatures were climbing as carbon emissions increased. And in 1975, geochemist Wallace Broecker gave this trend a name that has stuck: global warming.

Did you know

Since the Industrial Revolution, roughly the middle of the 19th century onwards, the Earth has witnessed a temperature rise of around 1.4°C to 1.5°C. While that might not sound like a lot when you consider that every year, the difference between summer and winter temperatures in major cities in Western Europe can easily be more than ten times that.

However, the figure is significant because the difference in temperature between summer and winter is due to local variations that have occurred historically in the absence of global warming, so they are not relevant. What is important here is that the baseline temperature is rising. On average, everywhere is getting warmer.

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