Despite what impressions you may get from the media coverage, the science of global warming and associated climate change is actually well understood. There are still disagreements about rate climate changes that will cause global warming will occur and there are political disagreements about what should do about it, but that doesn’t detract from the underlying physics and chemistry of the problem.
What we do know about the climate system, and have since 1824, is that the planet is affected by a “greenhouse effect,” where some of its radiated heat is reflected from the atmosphere to the surface. This effect causes the planet to heat up more than would be expected if it simply received and reflected the sun’s energy. This additional heat is causing the ice to melt, which will raise sea levels and change weather patterns.
We also know that the strength of this greenhouse effect is enhanced 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 known as greenhouse gases, or GHGs for short, and each has an impact on the amount of additional heat 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, CFCs were previously used in refrigerators and as aerosol propellants. Its presence in the atmosphere was identified as the cause of the appearance of a hole in the Earth’s ozone layer, which protects the Earth’s surface from some of the most dangerous wavelengths of solar radiation. Its use was banned in an international treaty signed in Montreal in 1987 and its concentration in the atmosphere has now started to decline, an encouraging success story that we must 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 level of concentration has increased considerably and the rate of increase in recent years has increased, so that they now exceed 390, about a third more than the long-term average.
Many human activities use energy generated from the burning of fossil fuels and this has been the main source of the increases.
- The use of coal, oil and gas to generate our electricity and gasoline, along with diesel and kerosene to power our transportation, has dumped billions of tons of carbon dioxide into the atmosphere that was previously trapped as fossil fuels.
- Logging and slash-and-burn to gain more farmland has added to the problem, but fossil fuels have created almost three and a half times as much.
- Raising animals for food and dumping our waste to rot in hidden pits has generated millions of tons of methane, another carbon compound whose ability to reflect heat back to the surface is almost 25 times more powerful than CO2, but still it accounts for only about a quarter of the impact of fossil fuels.
- Using oil-based fertilizers releases another greenhouse gas, nitrous oxide, which many of us have experienced as the “laughing gas” used in anesthetics in dentists and hospitals. Nitrous oxide is nearly 300 times more potent than CO2, but fortunately the amounts in the atmosphere are much smaller, accounting for less than 10% of greenhouse gases, even when taking into account its extra potency.
The simple truth is that the most important source of increased concentrations is that group of remarkably cheap, highly concentrated, and quite convenient fuels; coal, oil and gas.
Once you understand this, it doesn’t take long to understand why people are so willing to deny the existence of global warming. The world economy is dominated by companies that produce oil or gas or use their derivatives: it is almost impossible to imagine modern life without fossil fuels. But here is the most basic of all errors in the argument. Fossil fuels are not the only source of energy available to us. There is enough energy from the sun reaching the planet in one hour to power all human activities for an entire year. The real challenge is how we reorganize our political and economic systems to harness that energy and reclaim a safe climate for all of us.