Donnachadh McCarthy: Keeping up with carbon jargon

"Is it zero carbon or carbon neutral? Yes it is – no it isn't!" Judging by readers' emails, there seem to be a lot of arguments going on around this newfangled eco-jargon. This is not surprising, as it is only in the last couple of years that the public started talking about their carbon emissions, as the severity of the crisis started to dawn on us. A new terminology is being developed on the hoof.

Many of the new words used to convey these ideas are not yet clearly defined. Let us shed a little light, so the next time you are chatting about the climate crisis in the pub, you will have a handle on the terminology.

A zero-carbon house emits no carbon dioxide for energy use. It uses no fossil fuels for heating, hot water, cooking or electricity. No oil, gas, coal, anthracite, kerosene or even peat can be used. It doesn't even burn wood, even though it is not a fossil fuel, as wood releases CO2 when burnt. The term generally excludes CO2 emissions associated with actually building it or construction materials used.

However, a carbon-neutral home, unlike a zero-carbon home, may use some fossil fuels, as long as its energy use does not result in an increase in total atmospheric carbon dioxide. Therefore, if it uses natural gas for cooking but is a net exporter of an equivalent amount of green electricity from solar electric panels on the roof, it can be carbon neutral.

What can be a little confusing is that a carbon-neutral home can also burn wood, without having to offset it with excess green-energy. This is because the CO2 released is that stored during the lifetime of the tree. The total amount of CO2 in the atmosphere prior to the tree being planted and after it is burnt remains the same.

There is an important caveat. The wood must be from a forest where the trees cut down are replaced. Otherwise there will be a net increase in the total CO2 in the atmosphere.

As the average tree stores about one ton of CO2 during its lifetime, this means that rainforests being demolished in Brazil to clear land for soya beans for the European cow-herd and in Indonesia for palm oil for western food-additives are amongst the largest emitters of CO2 globally.

Frankly, there are still ongoing debates as to what these terms exactly mean. The Government, which wants all new homes to be carbon neutral by 2016, is considering whether a home is carbon neutral if the renewable energy is produced elsewhere. A Cardiff developer might claim her new development in Cardiff was carbon neutral, despite it having gas boilers, because she had built a dedicated wind turbine in Pembrokeshire, which produced an equivalent amount of green electricity to the gas burnt by the development.

Whilst laudable, I feel this would devalue the term "carbon-neutral home". An alternative needs to be invented such as "carbon-offset home", but that is another debate.

Donnachadh McCarthy runs an eco-auditing consultancy and is author of 'Easy Eco-auditing'. www.3acorns.co.uk