Climate Change: The science

The so-called greenhouse effect is essentially the trapping of reflected solar energy (infra-red radiation) by ‘greenhouse gases’. We actually need greenhouse gases in our atmosphere, otherwise the average temperature on earth would be about -18°C and so too cold for life. Unfortunately, in the last 200 years or so, human activities like the burning of fossil fuels have pumped huge amounts of extra greenhouse gas into the atmosphere, enhancing the greenhouse effect and so warming up the planet.

Useful links on climate change science:

The greenhouse gases get their name because they are particularly good at intercepting the heat radiated from our planet’s surface. The most important greenhouse gas is actually water vapour. Human activities don’t have a big direct effect on the amounts of water vapour in our atmosphere, but it is through our increasing emissions of the other leading greenhouse gases – carbon dioxide, methane and nitrous oxide – that we are raising global temperatures and, as a result, leading to more water vapour in the atmosphere too.

The key human sources of carbon dioxide emissions are fossil fuel-burning, land-use change, and industrial processes, such as cement production.

Since the industrial revolution, concentrations of carbon dioxide in our atmosphere have increased by more than 30%, methane concentrations have doubled, and levels of nitrous oxide have risen by 15%. Before the industrial revolution concentrations of carbon dioxide were about 280 part per million (ppm), today they are at 380ppm and rising fast (see the US National Oceanic and Atmospheric Administration for up-to-date changes). Ice-core records can tell us how concentrations of carbon dioxide have changed over the last 650,000 years. In that whole time they have never been anywhere near as high as they are today. We are now living in an atmosphere never before experienced by our species, a new era on the earth’s history where the actions of humans is determining the global climate: the Anthropocene. For graphs showing the rapid rise in carbon dioxide see Greenhouse Gas Online and the Carbon Dioxide Information Analysis Center.

If we continue to follow the traditional pathway of economic development, that based on fossil fuel burning, by the end of the 21st century, we may see carbon dioxide concentrations topping 800ppm – more than three times the pre-industrial level as shown on the graphs on the Greenhouse Gas Online website.

By increasing our atmosphere’s ability to absorb infra-red energy, our greenhouse emissions are disturbing the way the climate maintains the balance between incoming and outgoing energy. A doubling of the concentration of greenhouse gases (predicted in the next 100 years) would, if nothing else changed, reduce the rate at which the planet can shed energy into space by about 2 %. And while 2 % doesn’t sound much, across the entire earth it is equivalent to trapping the energy content of about 3 million tons of oil every 10 minutes – that’s an awful lot of heat.

Exactly how much the planet will heat up during the 21st century remains the focus of a great deal of debate and research. Any such predictions require assumptions to be made about how long greenhouse gas emissions will continue to increase, and how the many inter-linked systems that determine the earth’s climate will react to warmer temperatures and more carbon dioxide (see, for instance, the ice albedo effect. All the models agree on one thing at least: it will get warmer. Global temperatures have already increased by 0.6OC in the last 100 years. At present, our best estimate is that we will see a global temperature increase of between 2 and 6oC during this century (see this BBC webpage).

It is this rapid and significant increase in global temperature that drives climate change, and its potentially catastrophic impacts.