In early November 2021 much of the world’s media was focussed on the Glasgow Climate Change Conference (also known as COP26). As most of you will know, its key objectives were to get individual states to commit to reduce their greenhouse gas emissions, to end deforestation and to plan to move away from fossil fuel towards greener sources of energy. The overall goal being to reduce the global temperature rise which has happened over the last 100 years or so as a result of human activity. Much has been written in the media about the outcome of the conference, therefore I won’t repeat it here. The statement by the UN Secretary General gives a good overview.
Sadly, agreements made at Previous UN conferences to reduce greenhouse gases, in particular the Kyoto protocol in 1997 and the Paris agreement of 2015 have achieved very little. Although the COP26 target of limiting the global average temperature rise to 1.5oC from pre-industrial levels is claimed by some to be “still within reach”, it seems very unlikely it will be achieved. A recent article in Nature made the case that, even if the pledges announced in the Glasgow Climate Summit are implemented, average global temperatures will still rise by 2.4oC by the year 2100. An article by a group of scientists who call themselves the Climate Action Tracker concluded that, based upon current behaviour, the likely global temperature rise from pre-industrial levels will be between 2oC and 3.6oC by the end of the century.
Image credit Climate Action Tracker
For the remainder of this post I’ll talk about how the concentration of the greenhouse gas which has contributed most to global warming, carbon dioxide, has risen in recent years and how it continues to rise rapidly because of the lack of effective action at a global level.
Carbon dioxide (chemical formula CO2) is released when fuels containing carbon (such as coal, oil and natural gas) are burnt. In addition, living creatures produce carbon dioxide when they respire. Carbon dioxide is removed from the atmosphere by plant life through photosynthesis. This is when carbon dioxide and water, using the energy from sunlight, combine together to produce complex carbohydrates (starches), releasing oxygen in the process.
The Rise in Carbon Dioxide levels
The graph below plots the mean atmospheric CO2 , measured in parts per million (ppm), since 2016. The red dots represent the CO2 level in the middle of the month.
Data from https://gml.noaa.gov/ccgg/trends/
One interesting trend is the seasonal variation in carbon dioxide levels. This is a consequence of there being much more vegetation in the higher latitudes of the Northern Hemisphere compared to the equivalent latitudes in the Southern Hemisphere, which are mainly covered in deep ocean. In April and May, atmospheric CO2 levels are at their highest. As the Northern Hemisphere plant growth season progresses, CO2 levels fall because more CO2 is removed from the atmosphere by photosynthesis than is added, with the minimum CO2 level being reached in September. From October until [Northern Hemisphere] spring there is comparatively little plant growth in the Northern Hemisphere and CO2 levels rise.
In the graph above, the black line shows the CO2 levels smoothed out to remove this seasonal variation. This shows a steady rise in the average CO2 levels. This is even more evident if we look below at the pattern over the last sixty years.
Data from https://gml.noaa.gov/ccgg/trends/
There has been a rise in the CO2 levels from around 317 ppm in 1960 to 414 ppm in 2020 – an increase of 32%. The increase has been a result of two factors:
- The greater consumption of fossil fuels – thus pumping more and more CO2 into the atmosphere
- Clearing of large areas of forest and woodland (deforestation) has reduced the amount of CO2. removed from the atmosphere.
Worse still, the rate of increase of CO2 levels is also rising.
- Between 1960 and 1965 the atmospheric CO2 concentration rose from 316.9 ppm to 320.0 ppm – a rise of 3.1 ppm.
- However, between 2015 and 2020 it rose from 401.0 ppm to 414.2 ppm – a rise of 13.2 ppm.
With a growing population (in 1960 the world population was 3 billion and today it is nearly 8 billion) and rising living standards, we as a species have been producing more CO2 and (as I’ve said before) we’ve reduced a significant fraction of the Earth’s surface covered by woodland which removes it.
According to an article in Nature, in 2019 deforestation in Brazil spiked. Nearly 10,000 km2 of forest was destroyed as the country put economic growth before protecting the rainforest – the largest loss of rainforest in a decade.
Rise in the use of Fossil Fuels
The diagram below shows the amount of CO2 emittedby burning fossil fuels. At present, 35 billion tonnes are released into the atmosphere per year, which equates to roughly 4.5 tonnes for each person on Earth.
Coal – the largest contributor to carbon dioxide emissions
Coal consists mostly of carbon with variable amounts of other elements, chiefly hydrogen, sulfur, oxygen, and nitrogen. It is formed when dead plant matter decays firstly into peat and is then converted to coal by the heat and pressure of deep burial over millions of years. Coal is the largest contributor to CO2 emissions. Burning coal has other unpleasant effects. It produces smoke and toxic compounds which are responsible for air pollution and are generally hazardous to human health. One of the toxic compounds is the poisonous gas sulfur dioxide which is converted to sulfuric acid – responsible for acid rain. The graph below shows world coal consumption between 1990 and 2020. As you can see, coal consumption peaked in 2013 and has since declined slightly. The reduction in Europe and North America has been counteracted by the rise in Asia, particularly in the rapidly growing economies of India and China.
Change in coal consumption from 1990 to 2020. The vertical axis is in megatonne oil equivalents (one megatonne oil equivalent is equal to about 11.6 billion kwh or 11.6 Terawatt hours)
To have a realistic chance of meeting the Paris Agreement’s 1.5˚C warming limit, there would need to be an agreement to phase out fired power stations by 2030 in the OECD countries, and globally by 2040. This will not happen. Many countries including: China, India, Indonesia, Vietnam, Japan, South Korea and Australia, have plans which imply that coal will be a major contributor to electricity generation in 2030. In fact India intends to increase its domestic coal production over the next few years to meet its rapidly increasing energy demands. Both India and China insisted that the final wording of the COP26 agreement included the rather ambiguous statement “phase down coal” rather than the stronger “phase out coal”.
Oil – rising consumption
Crude oil consists mainly of hydrocarbons (compounds of hydrogen and carbon). It is converted in refineries into lighter hydrocarbons which are used for fuel and industrial processes. When hydrocarbons are burnt they produce carbon dioxide and water. (Small amounts of other toxic compounds are produced as well.)
Consumption of oil has steadily increased over the last 30 years, although there was a drop in 2020 due to the covid pandemic. When the world’s economy recovers, it is likely that consumption will increase – unless urgent action is taken.
If we look at the world as a whole, most of the increase has been in Asia. A key factor has been the rise in living standards in China and India, which have a combined population of nearly three billion.
Much of the world’s crude oil is refined into fuel for motor vehicles, mainly. gasoline (known as petrol in the UK) or diesel. To reduce CO2 emissions many countries have plans to move away from the internal combustion engine to electric vehicles (EVs). The UK intends to ban the sale of new petrol and diesel cars and vans by the year 2030, although new hybrid cars can be sold until 2035. Many nations made the pledge in Glasgow that new car and van sales would be EV-only by 2040. Sadly, many major countries did not do this. The noticeable countries which were not willing to commit to this target included Russia, China, Australia , (somewhat surprisingly ) Germany and the largest car market in the world the USA.
Natural Gas – rapidly rising consumption
Natural gas typically consists of around 85% to 90% of the hydrocarbon gas methane (which itself is a potent greenhouse gas). The remainder mainly consists of heavier hydrocarbon gases, including ethane, propane and butane. Being a mix of hydrocarbons, natural gas burns to produce carbon dioxide and water. It is a relatively clean fuel and produces little in the way of other pollutants.
The vertical axis is measured in billion cubic metres (bcm) of gas. One bcm is equivalent to 10.6 billion kw/h or 10.6 Tw/h
Natural gas consumption has increased steadily over the last 30 years. In the UK, which is fairly typical of Europe, natural gas provides 84% of its heating needs and I (like most of the UK’s population) live in a home heated by gas. Although the UK will ban new houses from being heated by gas in 2025, gas boilers can to be sold until 2035 to be fitted to existing accommodation . This means that, given the lifetime of a boiler is typically 15-20 years, in 2050 a substantial fraction of UK homes will still be heated by gas. As coal-fired power stations have been phased out, the amount of electricity generated by natural gas has increased and today 34.5% of the UK’s electricity is generated by burning natural gas.
The increasing use of natural gas does not fit with a goal of drastically reducing net CO2 emissions to zero. Although natural gas produces less CO2 and far less toxic compounds such as sulfur dioxide than coal, to dramatically reduce CO2 emissions it needs to be phased out globally in the coming decades. However, at present this is not happening. In Southeast Asia, heavily coal-dependent countries are now considering a switch from coal to gas, rather than coal to renewables. Large infrastructure projects for natural gas are under development in Europe (e.g. Nord Stream 2 for imports from Russia), Canada (expansions of the existing pipeline network to deliver gas for export), and USA (increasing the transport of liquid natural gas (LNG) ), and many African countries are promoting the increased production and use of natural gas.
Another issue with natural gas is that because methane is a gas at normal conditions (it boils at -162 oC) it has a low density. At room temperature and standard pressure, one tonne of methane has a volume 1500 cubic metres, whereas one tonne of petrol (gasoline) takes up 1.3 cubic metres. If large quantities of methane are to be stored it needs to be kept at low temperatures in liquid form or compressed to high pressures. This makes storage more expensive than oil or coal. Most countries in Europe don’t have the capability to stockpile large amounts of natural gas, for example to cover a winter’s demand, and are thus vulnerable to supply issues.
And finally …..
I hope you’ve found this post interesting. Unfortunately, at the moment the chances of reducing the carbon dioxide levels in the atmosphere over the next twenty years or so don’t look particularly promising. There are the competing objectives of individual countries seeking to maximise their short-term economic growth on the one hand and global need to reduce carbon dioxide emissions on the other hand
Also, although carbon dioxide is the main greenhouse gas contributing towards global warming, it isn’t the only one. In a future post I’ll talk about the next most important greenhouse gas: methane.