If someone was to ask ‘What keeps the earth warm?’ almost all of us would answer, perhaps without thinking, ‘the sun’. In this we would either be wrong or at least only partially correct. For although the original energy source is indeed the sun what keeps the earth warm is the greenhouse effect or more accurately a blanket of gases that allow the suns energy to reach the surface of the earth but prevents it from escaping back out of the atmosphere.
The Greenhouse Effect was discovered by French mathematician Joseph Fourier in about 1820 when he calculated that given the size of the earth and the distance of the earth from the sun the average temperature should have been a lot colder than it actually was. (Some calculations have the earth about 30 degrees cooler without the presence of the greenhouse effect, about the same temperature as Mars. These temperatures would have the earth as a ball of ice making it impossible for life as we know it on the planet.) Fourier postulated that there were other insulating factors present that helped the earth retain its heat and kept it much warmer than it would otherwise be. He had discovered, though not named, the Greenhouse Effect.
The Greenhouse Effect is the main physical law underpinning the science of climate change. Since Fourier other scientists have identified the main greenhouse gases – carbon dioxide and methane – (Tyndall) and made calculations as to how much increasing greenhouse gases will warm the planet (Arrhenious). These experiments and calculations have been repeated and refined many times since but have generally stood the test of time.
The relevance of the greenhouse effect to climate change and to global temperatures is obvious. I use the analogy of a playground see-saw where there is a balance between greenhouse gases and global temperatures giving a nice level for human existence. The see-saw has more or less been in balance for 10,000 years in an age known as the Holocene which has seen the rise of human civilisation. The see-saw analogy shows that if you reduce greenhouse gases the temperature goes down, if you increase them the temperature goes up.
What is clear and measured is that the by burning fossil fuels we have been pouring extra greenhouse gases into the atmosphere since the start of the industrial revolution. These greenhouse gases have been accurately measured since 1957 and show a steady increase. The science states that the earth will consequently warm as measurements from major scientific bodies across the earth have also established. There can be no debate about this. It is all about how bad the consequences of global warming will be and in particular the unknown and unintended consequences. We should be urgently preparing for the worst case scenarios.