Due to the senseless lies propagated by a minority of very vocal global warming denialists, there is a lot of misinformation and ignorance among people about the current phase of anthropogenic global warming. So, this post is a down-to-the-basics summary of global warming.
In a nutshell, carbon dioxide is a greenhouse gas. Its concentration in the atmosphere is rising due to additional input from human sources, causing the greenhouse effect to get intensified and the Earth to get warmer.
This is not a new-fangled insight. In fact, back in 1824, Joseph Fourier calculated that heat from the Sun is not enough to keep the Earth as warm as it is. There must be some other effect, and he surmised that the atmosphere also helped with keeping the planet warm. This was the greenhouse effect – just as the glass of a greenhouse keep the interior warm by trapping the Sun’s heat, so does the atmosphere.
John Tyndall discovered how the atmosphere does this in Tyndall (1859). There are gases in the atmosphere, notably water vapour and carbon dioxide, that allow sunlight to pass through them, but absorb infrared. Infrared is heat. So what happens with the Earth? Sunlight goes through the atmosphere, hits the ground and warms it up. As a result of this warming, infrared light is emitted, but the greenhouse gases absorb them instead of allowing them into to space. In other words, the heat emitted from the ground is trapped. In addition, the warming of the greenhouse gases also causes them to emit infrared, so there are two sources of warming.
So by the mid-1800s, the greenhouse effect’s existence and basic functioning was settled. The next step in our understanding came from famous chemist Svante Arrhenius in 1896. In Arrhenius (1896), he calculated that increasing CO2 concentrations will lead to an increased warming effect, and went further by saying that the burning of fossil fuels, by injecting CO2 into the atmosphere, is going to cause increased warming.
Fast forward to the modern era, and this prediction is confirmed. Starting from Keeling (1958) and in tons of studies since then, atmospheric CO2 has been measured in great detail and in all places and situations around the world. Carbon dioxide levels are, beyond the shadow of a doubt, rising yearly.
Concurrent with this, and agreeing with Arrhenius’s prediction, the instrumental records from land surface stations, sea surface readings, boreholes, ice cores, balloons, and satellites all show the average global temperature increasing by the year, tracking the increases in CO2. Hence, we can say with confidence that the Earth is warming, and it’s due to human influence, as the current major source of the extra CO2 is traced back to the use of fossil fuels. In essence, what we are doing is restoring the atmosphere of that was present when the fossil fuels formed (especially the Carboniferous coal swamps), and that’s bad because the infrastructure of human civilisation evolved at a time when CO2 levels were very low – adapting to a high CO2 world is going to take drastic changes.
Of course, there are many more greenhouse gases. But carbon dioxide is the one that’s emitted the most, hence why we concentrate on it.
The world is changing due to our inadvertent messing around with the climate. The ice caps are slowly melting – we will soon be able to have an ice-free Arctic in the summer (which will have many knock-on effects on the world climate). The biosphere is reacting dynamically to the changes, with phenologies and migration patterns changing, which is leading to the infilitration of tropical diseases into temperate zones. Ecosystem zones are shifting, with deserts and treelines expanding.
The land that we depend on to sustain human civilisation through agriculture is disappearing at alarming rates. In the 1970s, 12% of the Earth was classified as very dry. Now it’s over 30% (Dai et al., 2004), and it’s not stopping there.
Some say that citing such statistics is deceptive, as the Earth doesn’t care. Of course the Earth doesn’t care. The only thing that is at jeopardy here is human civilisation (and countless species, but let’s keep it close to heart). The only reason why we harp on about global warming is so that we may be able to continue prospering as a species on this planet. We need to change our lifestyles, we need to ramp up technology and revitalise agriculture with widespread GMO use, we need to switch to clean energies (nuclear, then renewables) to mitigate greenhouse gas emissions. These changes cannot wait any more, they need to happen now. Actually, they should have happened decades ago, but hey, who listens to scientists anyway?
Arrhenius S. 1896. XXXI. On the influence of carbonic acid in the air upon the temperature of the ground. Philosophical Magazine Series 5 41, 237-276.
Dai A, Trenberth KE & Qian T. 2004. A Global Dataset of Palmer Drought Severity Index for 1870–2002: Relationship with Soil Moisture and Effects of Surface Warming. Journal of Hydrometeorology 5, 1117-1130.
Fourier J. 1824. Mémoire due les températures du globe terrestre et des espaces planétaires. Annales de Chémie et de Physique 3ème série 27, 136-167.
Keeling CD. 1958. The concentration and isotopic abundances of atmospheric carbon dioxide in rural areas. Geochimica et Cosmochimica Acta 13, 322-334.
Tyndall J. 1859. Note on the Transmission of Radiant Heat through Gaseous Bodies. Proceedings of the Royal Society of London 10, 37-39.