widely recognised challenges our planet is facing and we are all becoming increasingly familiar with what greenhouse gases are, what they do and how we can reduce emissions. But you have probably never come across the following five things about greenhouse gas emissions:
- Carbon dioxide is the most commonly emitted greenhouse gas, but not the most potent
According to the Intergovernmental Panel for Climate Change, carbon dioxide is the most important greenhouse gas emitted by humans, accounting for 54.7% of greenhouse gas emissions. While carbon dioxide accounts for the highest percentage of greenhouse gases, it is not the most potent one. Methane, the second largest greenhouse gas accounting for 30% of overall emissions, is a much more potent greenhouse gas as it can trap 20% more heat than the same amount of carbon dioxide. Having said that, methane stays in the atmosphere for 12 years whereas carbon dioxide anywhere from 50 to thousands of years[sc:1].
- Water vapour is a greenhouse gas and the biggest contributor to the greenhouse effect
Water vapour is naturally present in the atmosphere and according to scientific evidence, it is the biggest overall contributor to the greenhouse effect. As temperatures rise, more water evaporates from the earth’s surface and becomes vapour in the atmosphere. More water vapour leads to more warming, creating a positive feedback loop where warming causes more changes that lead to even more warming. So, the amount of water vapour that can be found at any one time in the atmosphere, and the extent to which it contributes to the greenhouse effect, depends on how warm our planet gets. Crucially, however, it is excess carbon dioxide which accumulates and warms the atmosphere that in turn raises water vapour levels causing further warming. So the impact of water vapour is strongly related to the amount of other greenhouse gases in the air[sc:2].
- Carbon dioxide’s potential to contribute to greenhouse effect was first quantified in 1896
Swedish physicist Svante Arrhenius, who later on was awarded the Nobel Prize for Chemistry, was the first to try to measure the contribution of carbon dioxide to the greenhouse effect and to examine whether differences in the concentration of “carbonic acid”, as carbon dioxide was known at the time, could have contributed to long-term changes in our climate. His paper, “On the Influence of Carbonic Acid in the Air upon the Temperature of the Ground”, was published in The London, Edinburgh and Dublin Philosophical Magazine and Journal of Science in 1896. In later papers, Arrhenius linked more clearly the fact that burning of fossil fuels will cause global warming[sc:3].
- Carbon trapped in permafrost may not be there for long
As our planet continues to get warmer, scientists are looking at the Arctic to understand the impacts of higher temperatures. But it is not just the icecaps that they are worried about. Permafrost (perennially frozen) soils underlie much of the Arctic where due to the extreme cold and wet conditions dead plants and animals that grow when the top layer of the soil thaws in springtime, do not decompose. Instead they are trapped in the permafrost. So, while historically permafrost soils have stored more carbon than they have released, this may change if the planet continues warming up melting the permafrost. Scientists are unclear about the exact implications but estimate that if climate change causes the Arctic to get warmer and drier, most of the carbon that has been stored over the centuries will be released as carbon dioxide, but if it gets warmer and wetter, most will turn into methane. If permafrost soils melt, up to half of all the estimated organic carbon stored in the Earth’s soils may find its way into the atmosphere compounding global warming[sc:4].
- Warming “hiatus” despite increasing greenhouse gas emissions?
While there is consensus among scientists that an increase in greenhouse gases in the atmosphere will cause an increase in the global mean temperature, this will not necessarily be reflected in a smooth upward trend in temperature. Instead, there can be periods where temperature rises more rapidly and others where it does so more slowly.
Over the last 10-15 years, the global mean temperature trend has been relatively flat despite a continued rise in greenhouse gases in the atmosphere. The reason behind this is unclear. However, one theory suggests that heat has been stored in the ocean. The last decade or so has seen a period when east-to-west blowing Trade Winds in the Pacific Ocean have been relatively strong and this may have led to colder temperatures at the surface in the eastern Tropical Pacific, and an accumulation of warm water below the surface in the western tropical Pacific[sc:5].