Despite impressions you may gain from media coverage, the science of global warming and the associated climate change is actually well understood. There are still disagreements about the rate that the climate changes global warming will cause will happen and there are political disagreements about what we should do about it but that does not detract from the underlying physics and chemistry of the issue.
What we do know about the climate system, and have done since 1824, is that the planet is affected by a “greenhouse effect”, where some of its radiated heat is reflected back from the atmosphere to the surface. This effect makes the planet warmer than it would otherwise be expected to be if it were simply receiving and reflecting the sun’s energy. This extra heat is causing ice to melt, which will raise sea levels and the weather patterns to change.
We also know that the strength of this greenhouse effect is made stronger by the concentration of some gases in the atmosphere, notably carbon dioxide (CO2), methane, nitrous oxide and halogens also known as CFCs. Collectively these gases are referred to as green house gases or GHG for short and each has a impact on the amount of extra heat that the atmosphere retains.
This impact is related to the chemical properties of the gas and its abundance in the atmosphere. Some of the gases also have other impacts on the atmosphere: for example the CFC’s were formerly used in refrigerators and as propellants for aerosols. Their presence in the atmosphere was identified as the cause of a hole appearing in the Earth‘s ozone layer, which protects the Earth‘s surface from some of the more dangerous wavelengths of the sun’s radiation. Their use was banned in an international treaty signed in Montreal in 1987 and their concentration in the atmosphere has now started to decline, an encouraging success story which we need to emulate with the other gases.
For most of human history, the concentration of CO2 in the atmosphere has fluctuated between 200 and 280 parts per million (ppm). Since the Industrial Revolution, the concentration level has risen sharply and the rate of increase in recent years has gone up so they are now over 390, about a third higher than the long-term average.
Many human activities use power generated from burning fossil fuel and this has been the primary source of the increases.
- Using coal, oil and gas to generate our electricity and petrol, along with diesel and kerosene to power our transport, has dumped billions of tonnes of the carbon dioxide formerly trapped as fossil back into the atmosphere.
- Cutting down trees and slash-and-burn clearances to gain more farmland has added to the problem, but the fossil fuels have created nearly three and a half times as much.
- Breeding animals to feed ourselves and dumping our waste to rot in out-of-sight pits has generated millions of tonnes of methane, another carbon compound and one whose ability to reflect heat back to the surface is nearly 25 times more potent than CO2, but it still accounts for only about a quarter of the impact that the fossil fuels do.
- The use of oil-based fertilizers releases another greenhouse gas, nitrous oxide, which many of us have experienced as the ‘laughing gas’ used in anaesthetics at dentists and hospitals. Nitrous oxide is nearly 300 times more potent than CO2 but thankfully the quantities in the atmosphere are much smaller and it makes up less than 10% of the greenhouse gasses even when its additional potency is taken to account.
The simple truth is that the single biggest source of increased concentrations is that remarkably cheap, highly concentrated and fairly convenient group of fuels; coal, oil and gas.
Once you understand this, it doesn’t take long to understand why people are so keen to deny the existence of global warming. The world’s economy is dominated by companies that produce oil or gas or use its by-products: it is almost impossible to imagine modern life without fossil fuel. But here is the most basic of all the errors in the argument. Fossil fuels are not the only source of energy available to us. There is sufficient energy from the sun arriving on the planet in one hour to power all human activities for an entire year. The real challenge is how we rearrange our political and economic systems to harness that energy and reclaim a safe climate for all of us.