The key topics that will be addressed over the series include the impact of climate change, taxonomy of climate risk, the current regulatory landscape and misconceptions of climate risk. The aim of our first blog is to provide a brief introduction and overview to the science of climate change. We will describe what climate change is, what are the causes and what the potential implications are.
What is climate change and how it is related to global warming?
The average weather conditions over a period of time is referred to as a climate. If the average climate between two distinct periods of time differ then there is said to be a change in the climate. Colloquially “Climate Change” is the term used to refer to our presently warming climate, it is common to think of our current climate as the average of the past 30 years.
Today global temperatures can be estimated in sophisticated ways using modern equipment, for example using satellites. Estimating historic temperatures is more difficult but can be done through computer modelling studies, combining these can give time-series estimates of the global average temperature over the past few hundred years. Figure 1 is taken from the Intergovernmental Panel on Climate Change (IPCC) Sixth Assessment Report published in 2020 and it clearly shows that the global average temperatures have been increasing since the start of the industrial revolution (circa 1850).
Currently we are experiencing global annual average temperatures that are at least 1°C warmer than pre-industrial times. The IPCC report stated that the warming was unequivocally caused by human activity. Since the industrial revolution, humanity’s greenhouse gas (GHG) emissions have been driven by burning of fossil fuels to generate energy. It is the increased GHGs that are directly responsible for the warmer climate that we experience today and the predictions of even warmer climates in the future.
Source: IPCC Sixth Assessment Report Summary for Policy Makers
The greenhouse effect: keeping our planet warm.
Gases that are present in our atmosphere absorb and radiate heat and they do so at different wavelengths. The Earth receives its energy (heat) from the sun in the form of shortwave solar radiation. This radiation is absorbed by gases in the atmosphere and the surface and is eventually re-radiated back to space in the form of outgoing longwave radiation. On average the amount of incoming and outgoing radiation should approximately be equal to keep the temperature of the planet constant. Greenhouse gases absorb more shortwave radiation than they radiate away as longwave radiation causing an imbalance of incoming and outgoing radiation. Since the gases in the atmosphere retain more heat the average temperature of the planet increases as the concentration of GHGs increases. This process of greenhouse gases trapping warm air in the atmosphere is known as the greenhouse effect and is illustrated in Figure 2. The greenhouse effect is extremely important as without it Earth would be too cold to sustain human life.
Greenhouse gases are increasing
The majority of Earth’s atmosphere (99%) is composed primarily of Nitrogen and Oxygen. There are many other gases in the atmosphere that are present in small amounts. Carbon dioxide (CO2) is one of the most important trace gases for regulating climate as it is a greenhouse gas. This means that the more CO2 humanity produces the warmer the climate will get.
The Mauna Lao Observatory in Hawaii (of the Scripps Institution of Oceanography a facility of the National Oceanic and Atmospheric Administration) started recording the amount of carbon dioxide in the atmosphere in 19581. The Mauna Lao Observatory was chosen as the sits in the middle of the North Pacific Ocean far from any direct source of carbon dioxide production; since carbon dioxide is a well-mixed GHG these observations are representative of the global concentration of carbon dioxide in the atmosphere.
Figure 3(a) shows the monthly mean concentrations of carbon dioxide present in the atmosphere in units of parts per million as observed at the Mauna Loa observatory, since these records began there has been an increase in carbon dioxide due to the use of fossil fuels for energy production. To put this increase into context we can look at the long-term historical climate records that are constructed from ice-cores and are shown in Figure 3(b); this clearly shows that the current concentrations of carbon dioxide are unprecedented over the past 800,000 years. As the amount of GHGs in the atmosphere, such as carbon dioxide, increases so does the ability to trap heat in the Earth’s atmosphere; the planet then begins to continually increase in temperature and the human-induced increase in GHGs causes the dramatic rise in global mean temperatures as shown in Figure 1.
What are the consequences of global warming?
The increase in global average temperatures is crucially important for our current way of life as it has the power to cause disruption to long established atmospheric circulations. While not all the effects are yet fully understood and are still active areas of scientific research, it is clear that climate change is already having an effect. There are some clear fingerprints of a warmer climate evident today such as the visibly the melting Arctic sea-ice as shown in Figure 4, retreating glaciers and the melting of permafrost among many others.
A warmer climate will also affect the weather we experience; since many of the physical processes that drive our weather are caused by temperature differences, a warmer climate can directly influence the type of weather we get. For example, it is a well understood physical relationship that a warmer atmosphere can hold more moisture; therefore as the planet warms the atmosphere contains more moisture and this leads to heavier and more extreme rainfall.
It is not only our atmosphere that is affected by increases in greenhouse gases and temperature but also our oceans. The oceans make up 70% of Earth’s surface area and are also increasing in temperature. As the oceans warm they expand in volume this results in sea-level rise and threatens the very existence of some low-lying countries.
It is also likely that in a warming climate the frequency and severity of extreme weather events, such as (extra-)tropical cyclones, floods, heatwaves, droughts, hailstorms and wildfire will change. If these events become more frequent and/or more extreme there is the potential to cause massive humanitarian and economic disruption.
