Our climate has remained relatively stable for most of human history, apart from some important exceptions. This is because Earth’s energy balance, i.e., the balance between the amount of energy or heat it receives from the Sun and that lost to space mainly during darkness, has remained relatively stable for millennia. This balance is regulated by small amounts of gases in the atmosphere known as greenhouse gases (GHGs).
GHG emissions are the most significant contributor to climate change . As gases they are invisible, and they reside in the atmosphere for years to centuries. The atmospheric concentrations of the main GHGs i.e. carbon dioxide, methane, and nitrous oxide have remained relative stable for at least 800,000 years until the start of the industrial revolution. Since then they have increased at an unprecedented rate reaching levels that have not existed on Earth for likely millions of years.
Interestingly, the role of GHGs was discovered in the mid-19th Century by John Tyndall from Co. Carlow.
Carbon dioxide concentrations have increased by 40 per cent since pre-industrial times. This is primarily due to fossil fuel emissions but also from land-use changes which release carbon from biomass and soils. The increased emissions to the atmosphere of greenhouse gases mean that current levels of gases far exceed their natural ranges. This has the same effect as putting a blanket around the planet, trapping the warmth and not allowing it to escape. Here you can see the levels of certain greenhouse gases in the atmosphere over the last 2000 years.
Although GHG emissions are the most significant contributor to climate change, there are other components of the atmosphere that can also change the Earth’s energy balance. These include microscopic particles, dusts and clouds. The most rapid and dramatic changes to the energy balance have occurred when major volcanic eruptions launch large amounts of material into the upper atmosphere where it can reside for years. These reflect sunlight back to space, causing regional and global cooling. Massive volcano eruptions such as that of Mount Tambora in 1815 can have that effect. Such events can disturb our climate for one or two years but the reflective particles which cause this change eventually fall-out of the atmosphere or are captured in clouds and removed by rain fall.
The other large source of such particulates is human activities; specifically, combustion for heating, transport, and industry. Like the material which results from massive volcanic eruptions, these particulates fall, or are rained, out of the atmosphere. As they are not usually very high in the atmosphere, this happens over time. However, ongoing diverse combustion means that there is a relatively constant flow into the atmosphere which has increased since the industrial revolution. These particulates, which cause significant air quality problems, also have a cooling effect on the climate system. This increase in trapped energy in the Earth’s climate system is driving changes that are observed across worlds continents, islands and oceans.