What is climate change?

Climate change is the long-term change of the world’s weather systems. Climate is the general weather that is typical of an area. Rapid, damaging climate change has been increasing since the 1800s, when humans started to burn a large amount of fossil fuels (coal, oil and gas), cut down more forests than before and increased other damage to natural systems. Burning fossil fuels releases gases from the ground into the sky (the ‘atmosphere’). These gases make a blanket around the Earth, trapping heat. The blanket is warming our air, oceans, and land.

The 20 hottest years that have been recorded have all happened in the last 22 years. This heating up has created more extreme and unpredictable weather, and many other impacts on the lives of people and animals. The Earth’s climate has changed at other times in the past, over time, but this time it is very rapid, extreme, and is being caused by human activities.


Isn't climate change a natural change?

The change we are experiencing now in our world’s climate is not natural.

The change we are witnessing is much faster than previous changes. It is not part of natural climate fluctuations. If natural fluctuations were occurring, we would be in a cooling phase right now. Instead, the temperature of the planet is rising rapidly.

The natural carbon cycle that keeps so many of the Earth’s systems in balance has been thrown out of balance by humans digging up a staggering amount of carbon from the ground, burning it for electricity and transport, as well as releasing it through large-scale agriculture using chemicals and cutting down forests. Greenhouse gases are being released in massive amounts into the cycle causing cascading impacts on the temperature of the atmosphere, land and bodies of water and ice, creating more chaotic weather systems, and a less hospitable living environment.

Looking over the long history of this planet, the Earth’s climate has changed slowly, over 100s of millions of years. The change to the global climate that we are living through now has happened in just over 100 years. That means the current rise of CO2 and temperature is happening at a rate a million times faster than previous global changes. Humans and other species cannot evolve to cope with this rate of change.

Natural fluctuations

The Little Ice Age experienced by Medieval Europe and other short-term fluctuations over past centuries were small fluctuations of temperature, and they affected specific regions rather than the whole world, as it does now. Regular ocean-atmospheric cycles – such as El Niño, La Niña, and the Indian Ocean Dipole – are temporary fluctuations (for instance, El Niño is a warming of ocean surface temperatures in the tropical eastern Pacific for a few months every few years). These cycles bring temporary adjustments of weather in a region (worsening hurricanes in the United States, or causing a drier season across eastern Australia and the Pacific, for instance) but they do not alter the global, rapid upward rise of the temperature of the air, land and water and the flow-on effects of human-induced climate change.

The last time there was this much carbon dioxide gas (CO2) in the atmosphere, it was 8 Million years ago, before humans evolved. High levels of CO2 and other greenhouse gases in the atmosphere mean high global temperatures. We and most of Earth’s species are not adapted to cope with a very hot planet.


CO2 levels over millenia
This graph, based on the comparison of atmospheric samples contained in ice cores and more recent direct measurements, provides evidence that atmospheric CO2 has increased since the Industrial Revolution. (Credit: Luthi, D., et al.. 2008; Etheridge, D.M., et al. 2010; Vostok ice core data/J.R. Petit et al.; NOAA Mauna Loa CO2 record.) Image: NASA
© CC BY NC SA

How do we know the scientists are right?

It has been shown, over many decades, through the observations and work of tens of thousands of scientists, that rapid, dangerous climate change is underway and it is caused by human activity. The first explanations of these connections occurred in the 19th Century, and extremely detailed and long-lasting studies by many teams of dedicated climate scientists have increased at a great pace during the last half of the 20th Century, to now. Careful, traceable, repeatable, carefully-reviewed and widely-published studies continue to deepen our understanding of the workings of climate change. The evidence for human-induced climate change can be tracked clearly; there is no other explanation that holds up to scrutiny that can account for the rapid increase of CO2 in the atmosphere and the parallel warming of the planet.


What do the different terms mean?

Climate Emergency:

'a situation in which urgent action is required to reduce or halt climate change and avoid potentially irreversible environmental damage resulting from it’ (Oxford Dictionary)

Climate Change

long-term change to the world’s climate. The term is usually used to refer to the very rapid, damaging rise of temperature and extreme weather events that are occurring currently. The term also covers the slower phases of planetary climate change in the distant past.

Climate Crisis:

‘situation in which immediate action is needed to reduce or stop climate change and prevent serious and permanent damage to the environment’ (Oxford Dictionary)

Fossil Fuels

fuel (coal, oil, gas) formed in the earth from plant and animal matter. Burning coal, oil and gas releases the carbon that was stored underground into the atmosphere and oceans.

Global Warming:

the increase in temperature of the earth’s atmosphere that is caused by the increase of particular gases, especially carbon dioxide (Oxford Dictionary)

Greenhouse Effect:

the trapping of the sun’s heat by gasses in the Earth’s atmosphere. This makes the Earth warmer than it would be without the gasses. (NASA Climate Kids)


A History of the Science of Climate Change

Nineteenth Century discoveries: Joseph Fourier, Eunice Foote and John Tyndall.
The operation of greenhouse gases in Earth’s atmosphere has been studied over the past two centuries. The role of the atmosphere as a ‘blanket’, trapping heat, was demonstrated by Joseph John-Baptiste Fourier in the early 1820s. Regular instrumental recoding of atmospheric temperature began in the 1850s. The next milestone was reached by Eunice Foote, a scientist, inventor and campaigner for women’s rights, of New York State, who published her observations on the heat-trapping qualities of water (H2O) and Carbon Dioxide (CO2) in 1856. It appears that, rather than John Tyndall, Eunice Foote was the first scientist to propose that CO2 levels in the atmosphere changes atmospheric temperature. Three years later John Tydnall, an Irish physicist, mathematician, geologist and atmospheric scientist, made important strides in understanding of the heat-absorbing qualities of CO2 and water vapour in the atmosphere. This work was part of a large body of ground-breaking experimental and applied science, including developing a method for measuring particles based on his pioneering description of the scattering of light (the Tyndall Effect), an explanation for why the sky is blue and the first studies London air pollution.


Eunice Foote - On the heat in the Sun's Rays
The paper by Eunice Foote that first described the relations between CO2 (then called Carbonic Acid) and the atmosphere. Elisha Foote (1857) XXVII. On the heat in the sun's rays, The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science, 13:85, 167-172, DOI: 10.1080/14786445708642274 Image: N/A
© Public Domian

Twentieth Century discoveries: From Guy Callendar to the Keeling curve

Research, discussions, theories and counter-theories about the operation of CO2, the absorption of heat in the atmosphere and in the oceans continued through the decades that followed, between scientists (primarily in Europe, Britain and the United States). In the 1930s an engineer, Guy Callendar, tracked temperature records and sought to explain the rise that he detected. Measuring levels of atmospheric CO2, he proposed the rise in the levels of the gas as the cause of the warming. He also stated, as John Mason explains, that “in coming centuries there could be, a climate shift to a permanently warmer state.”

The rise of computing power in the 1950s enabled more analysis of atmosphere layers, and work to understand how each might absorb infra-red radiation. Gilbert Plass, physicist, confirmed that more CO2 would have a warming effect- and that doubling the levels would create warming of 3-4°C. Countering those who argued that excess CO2 would be absorbed by the oceans, he contended that it would remain in the atmosphere for thousands of years, and that if the emissions rates of the mid-1950s continued, we could expect to experience 1.1°C of warming per century.

A group of Swedish scientists at this time were recoding CO2 levels at a network of measuring stations but their results were troubled by additional data (‘noise’) that made it difficult to interpret the readings. By the 1950s, work by Seuss and Roger Revelle at the Scripps Institution of Oceanography, established that the ocean could not be expected to absorb all excess CO2emitted by human activities, and instigated a program to start gathering less ‘noisy’ readings on CO2 levels. In their 1956 publication they stated:

. . . human beings are now carrying out a large scale geophysical experiment of a kind that could not have happened in the past nor be reproduced in the future. Within a few centuries we are returning to the atmosphere and oceans the concentrated organic carbon stored in sedimentary rocks over hundreds of millions of years.

Revelle and Seuss teamed up with Charles David Keeling, a researcher in California, to establish observation stations in places like Antarctica and Hawaii, away from local human-made sources of CO2. While funding for the Antarctic stations ebbed away, the Hawaiian station at Mauna Loa has been continuously collecting data on high-level atmospheric conditions since the 1950s. In 1953 Keeling was able to establish a reliable baseline of recordings. The upward curve of CO2 that Keeling documented has informed climatologists following, and is widely known as “The Keeling Curve”.

Since Keeling the science of climate change has expanded and deepened. From the 1980s, scientists around the world made calls for restrictions on greenhouse gasses. In 1988 the world’s governments created a panel, the Intergovernmental Panel on Climate Change (IPCC). Hundreds of experts – soon thousands – donated their time to groups that studied data, created ever-more accurate models, to determine could be said with certainty to be going on. Computer modeller James Hansen addressed the US Congress in 1988 and raised the alarm, bringing the issues more substantially into public conversation. By 2001, the thousands of experts contributing to the IPCC’s reports concluded that it was much more likely than not that severe global warming was underway.


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