SENIORS CLIMATE ACTION NETWORK (SCAN)
Climate Change Explained
"Climate change is no longer some far-off problem; it is happening here; it is happening now." - President Barack Obama
The average temperature of the surface of our planet Earth is 15°C. Incoming solar radiation is absorbed by the Earth’s surface and is re-radiated back into the atmosphere as infrared energy which is trapped from fully escaping to outer space by carbon dioxide, water vapour, methane, and nitrous oxide in the atmosphere. These greenhouse gases create a greenhouse effect which help to keep the surface of Earth at a temperature about 33°C higher than it would be without an atmosphere. Life forms on Earth – flora and fauna – could not exist without greenhouse gases in the atmosphere because Earth would otherwise be a frozen planet with an average surface temperature of -18°C.
It is important to distinguish between climate and weather. Climate is a seasonal averaging of weather and weather is what is experienced on a particular day. Climate change refers to long-term changes in climate from season to season and the climate of Earth has fluctuated many times over millions of year. In the distant past the surface of Earth has been both hotter and colder. The last ice age ended about 10,000 years ago. When we now talk about global warming or climate change, we refer to the relatively recent sharp increase in the global average temperature near the Earth’s surface caused by increasing concentrations of greenhouse gases.
There are several factors which contribute to global warming and cooling. For example, the sun goes through an 11-year sunspot cycle during which it gets a little bit hotter an colder, but this change has a minor effect on the surface temperature of Earth. Eruptions of volcanoes have a cooling effect. Increases in global warming forces since the start of the industrial revolution in 1850 are due mainly to increases in human induced greenhouse gases. These global warming forces far outweigh variations in solar activity, natural variability, and volcanic activity as shown in Figure 1 below.
It is important to distinguish between climate and weather. Climate is a seasonal averaging of weather and weather is what is experienced on a particular day. Climate change refers to long-term changes in climate from season to season and the climate of Earth has fluctuated many times over millions of year. In the distant past the surface of Earth has been both hotter and colder. The last ice age ended about 10,000 years ago. When we now talk about global warming or climate change, we refer to the relatively recent sharp increase in the global average temperature near the Earth’s surface caused by increasing concentrations of greenhouse gases.
There are several factors which contribute to global warming and cooling. For example, the sun goes through an 11-year sunspot cycle during which it gets a little bit hotter an colder, but this change has a minor effect on the surface temperature of Earth. Eruptions of volcanoes have a cooling effect. Increases in global warming forces since the start of the industrial revolution in 1850 are due mainly to increases in human induced greenhouse gases. These global warming forces far outweigh variations in solar activity, natural variability, and volcanic activity as shown in Figure 1 below.
Figure 1: Forces affecting global warming
The role of carbon dioxide (CO2) in the atmosphere and the greenhouse gas effect was known over a century ago by scientists. Svante Arrhenius made the first quantitative prediction of global warming due to a hypothetical doubling of atmospheric carbon dioxide and published a paper on climate change in a peer reviewed international journal in 1896 as shown in Figure 2 below.
Figure 2: Svante Arrhenius April 1896
A few years later, the general public also became aware of the global warming effect of CO2 in the atmosphere due to the burning of fossil fuels. Figure 3 below shows an example of a publication in a New Zealand newspaper, The Rodney & Otamatea Times, published in 1912.
Figure 3: The Rodney & Otamatea Times 1912
By 2020 it was well established and accepted by most that climate change is a reality due to human induced emissions of greenhouse gas emissions (Myers et al. 2021). The Intergovernmental Panel on Climate Change’s (IPCC 2021) Sixth Assessment Report which represents the work of hundreds of leading experts in climate science, states that "it is unequivocal that human influence has warmed the atmosphere, ocean and land. Widespread and rapid changes in the atmosphere, ocean, cryosphere, and biosphere have occurred.”
There are many different sources of greenhouse gas emissions as shown in Figure 4 below. Most of these emissions are the result of burning fossil fuels.
There are many different sources of greenhouse gas emissions as shown in Figure 4 below. Most of these emissions are the result of burning fossil fuels.
Figure 4: The biggest sources of greenhouse gases
Goods and services use combinations of different forms of fossil fuels which emit different greenhouse gases to the atmosphere – carbon dioxide (CO2), methane (CH4), nitrous dioxide (N2O), etc. CO2 is a long-lived greenhouse gas which stays in the atmosphere for between 300 and 1,000 years before being absorbed by natural processes. Some greenhouse gases are short-lived and have a different impact on climate warming over time. These greenhouse gases are converted into carbon dioxide equivalents (CO2e) where CO2 has the value of one.
The average impact of methane on climate warming over 100 years is 25 times greater than CO2 and the CO2e value of 25 is used by the Intergovernmental Panel on Climate Change (IPCC), research publications, and many carbon footprint calculators. But the impact of methane on climate warming over 20 years is 84 times greater than CO2 and the next 20 years are the most critical years over which drastic reductions in all forms of greenhouse gas emissions are necessary. The short-term impact of methane is critical to take into account when the greenhouse gas emissions of food production are examined because ruminants (cows and sheep) belch out many tonnes of methane to the atmosphere each year.
Greenhouse gas emissions have increased substantially since the 1850s. Figure 5 below shows the growth in CO2 emissions by world regions.
The average impact of methane on climate warming over 100 years is 25 times greater than CO2 and the CO2e value of 25 is used by the Intergovernmental Panel on Climate Change (IPCC), research publications, and many carbon footprint calculators. But the impact of methane on climate warming over 20 years is 84 times greater than CO2 and the next 20 years are the most critical years over which drastic reductions in all forms of greenhouse gas emissions are necessary. The short-term impact of methane is critical to take into account when the greenhouse gas emissions of food production are examined because ruminants (cows and sheep) belch out many tonnes of methane to the atmosphere each year.
Greenhouse gas emissions have increased substantially since the 1850s. Figure 5 below shows the growth in CO2 emissions by world regions.
Figure 5: Global annual CO2-emissions by world regions 1850-2019
Growth rates in the use of fossil fuels and subsequent greenhouse gas emissions have varied from 1850 to 2019. Figure 5 above shows that greenhouse gas emissions released over the period of 29 years from 1990 to 2018 is almost equal to the annual sum of all historical emissions from 1850 until 1990.