Climate Change Explained

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.

Figure 1: Forces affecting global warming (Craig, ***)

The role of carbon dioxide (CO2) in the atmosphere and the greenhouse gas effect was known over a century ago by scientists. Svante Arrhenius published a paper on climate change in a peer reviewed international journal in 1896 as shown in Figure 2.

Have a look at Professor Iain Stewart's YouTube presentation "BBC Making Scotland's Landscape" which describes how Scottish scientists and engineers helped unwittingly set off a chain of events that today we know as climate change - a process that is transforming our atmosphere and warming our planet.

Figure 2: Svante Arrhenius April 1896

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.”

The 2015 Paris Agreement was adopted by a resolution of the United Nations General Assembly. The target of the2015 Paris Agreement was to hold the global average temperature to well below 2 degrees Celsius above pre-industrial levels and to pursue efforts to limit the temperature increases to 1.5 degrees Celsius. Reductions would be undertaken in accordance with the best science and on the basis of equity. It was recognised that the less-developed nations would require financial assistance from the well-developed nations. The 2015 Paris Agreement recognised that business-as-usual emissions of greenhouse gases must be curbed. Adoption of a carbon budget was agreed upon. The budget is an annual reducing budget, the total size of which is represented by the area under the curve of projected reductions in carbon dioxide emissions as shown in Figure 4.

Figure 4: Carbon Budget Required to Mitigate the Impact of Climate Change

Unfortunately, there is a smoke and mirror difference between agreement by world leaders and actual action. Action by our world leaders to mitigate the impact of climate change have been repeatedly delayed until the next meeting. Meeting after meeting has resulted in a lot of hot air. Greta Thunberg has summarised these meetings as being "blah, blah, blah:. The COP26 meeting held in November 2021 was no different. Over the last 50 years there have been over 34 climate conferences, a half dozen major international climate agreements and various scientist’s warnings. Greenhouse gases emissions have continued to accumulate in the atmosphere unabated. Action to match the words have so far been a dismal failure.

In 2019, New Zealand declared a Climate Emergency. As of April 2025, there has been so far no sweeping and rapid social change in New Zealand towards mitigating the impact of climate change. New Zealand’s Net Zero Carbon by 2050 policy essentially supports incremental adjustments to business as usual.

Figure 5: Global smoke and mirror response to climate change

There are many different sources of greenhouse gas emissions as shown in Figure 6. Most of these emissions are the result of burning fossil fuels.

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. CO₂is 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 (CO_2e) where CO₂has the value of one.

The average impact of methane on climate warming over 100 years is 25 times greater than CO₂ and the CO_2e 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.

Figure 6: The biggest sources of greenhouse gases (Al Gore, 2016)

Greenhouse gas emissions have increased substantially since the 1850s. Figure 7 shows the growth in CO₂ emissions by world regions.

Growth rates in the use of fossil fuels and subsequent greenhouse gas emissions have varied from 1850 to 2019.

Figure 7 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.

Figure 7: Global annual CO₂-emissions by world regions 1850-2019 (Chancel, 2021)

The impact of global warming can no longer be ignored. A rise in the global average temperature has resulted in hotter summers, rising sea temperatures, melting of polar ice, and subsequent rising sea levels. A warmer atmosphere contains more water which causes changes in weather patterns including increased storm activity and more severe rainfall. A warmer atmosphere also increases evaporation of moisture from the land during dry weather resulting in drought and heat waves.

The following photographs show typical examples of the impact of global warming.