# How much carbon dioxide?

When people talk about climate change and carbon dioxide, they often talk about tonnes of CO2 emitted from different facilities, countries or regions over different periods of time - often annually. Of course, when they describe emissions from power plants the units are most commonly in millions of tonnes per year. For countries, the units become hundreds of millions of tonnes per year and for regions it changes to gigatonnes per year. We all know that a million is a large number - so a 'giga' must be really big. So when we hear that global emissions of carbon dioxide in a recent year totalled over 30 gigatonnes (or 30 Gt), we know it is a lot of CO2 - but do we really have any serious understanding of just how much that is? It is, of course, 30,000,000,000 tonnes - but who knows how much space a tonne of carbon dioxide occupies?

This can be calculated using Avagadro's Hypothesis that one mole of a gas occupies 22.4 litres at 'standard temperature and pressure' (STP - zero degrees Celsius and one atmosphere of air pressure - or a freezing cold day at sea-level). One mole of CO2 weighs 44 grams. So 1 gram of CO2 will occupy 22.4/44 litres at STP and 1 kilogram will occupy a space of (1000 times 22.4/44) litres which is 509 litres. One tonne of CO2 will, therefore, have a volume of 1000 x 509 litres or 509 cubic metres (m3).

My local swimming baths is 25 metres long and 15 metres wide, so one tonne of CO2 will fill it to a depth of 1.36 metres - which is about the depth of the water in the swimming pool.

At present, the largest single point source of CO2 emissions in Europe is the Belchatow lignite-fired power plant in Poland. When all of its units are operating, it will be emitting over 33 million tonnes of CO2 each year. There are also two plants in Germany that emit close to 30 million tonnes/year and the largest plant in the UK emits around 20 million tonnes/year - a similar size to the largest of the Australian coal-fired power plants.

A simple mathematical calculation shows that there are 31, 536,000 seconds in one year. So the Belchatow power plant will emit over one tonne of CO2 every second. In other words, it would emit enough CO2 to overfill my local swimming baths every second of every day. Another way of looking at this much CO2 is how long it would take the power plant to fill a 'super stadium' - such as the new 100,000-seater Wembley (1.4 million m3) or the massive Melbourne Cricket Ground (MCG - 1.7 million m3). The answer is 37 minutes for Wembley and 55 minutes for the MCG. So one - admittedly very large - power plant could totally fill Wembley Stadium with CO2 thirty-nine times a day, every day, every year (or the MCG 26 times each day, every day, every year).

The largest CO2 emitting country in Europe is Germany. The German power sector emits 345 million tonnes of CO2/year - which is 945,000 tonnes each day. This could totally fill Wembley Stadium 422 times every day - or once every five minutes. The emissions from the German industrial sector could fill it an additional 212 times each day. Of course, this is only a part of the story. Total emissions are significantly higher as they must include all forms of transport, domestic and agricultural emissions - but many of these emissions are difficult or near impossible to capture and store as they are much more dispersed.

Australian national emissions, for example, are around 540 million tonnes of CO2/year, but only around 200 million tonnes of these come from the power sector. Even so, the Australian power sector alone emits sufficient carbon dioxide to completely fill the MCG 164 times each day (or every nine minutes).

So when we talk quite nonchalantly about a gigatonne of CO2 in a year, we mean enough CO2 to fill Wembley stadium about four hundred and fifty thousand times (yes, 450,000) each year or three hundred thousand (300,000) MCGs.

Do the math for a stadium near you!

Of course, you still have to multiply the number you get by 30 as our global annual emissions exceed 30 gigatonnes - and they are increasing every year.

Did we really think we could pump these waste gases into our atmosphere without having any impact on the air that we breathe or our climate? How much longer do you think we can continue to do it? Is it not much more sensible - and responsible - to capture as much of the gas as we can, compress it (reducing its volume by 600 times or more) and pump it deep underground where it will stay without any negative effects on us or our environment?

Take a deep breath! During the time you have been reading this (assuming approximately five minutes), then globally we have emitted enough carbon dioxide to fill Wembley stadium 130 times.....