Why is our climate changing?

The Intergovernmental Panel on Climate Change (IPCC) confirms that changes in our climate are very likely caused by increased volumes of greenhouse gases, such as carbon dioxide, nitrous oxide and methane, in the atmosphere.

Ordinarily, solar energy from the sun passes through the Earth's atmosphere, and is absorbed at the surface. As it warms, the surface emits infra-red radiation. Most of that radiation is absorbed by greenhouse gases in the atmosphere, but enough escapes it to balance the net incoming solar energy. Over the long term, this equilibrium keeps temperatures relatively stable.

But when the concentration of greenhouse gases in the atmosphere increases, more radiation is trapped, and some of it is re-directed back to the lower atmosphere and surface. This drives the climate to a new, warmer balance.

The most abundant greenhouse gases are water vapour, carbon dioxide, nitrous oxide, methane and ozone. The increase in carbon dioxide is mainly the result of our burning more fossil fuels, such as petroleum and coal, even as we fell more and more forests, which would otherwise have helped absorb those gases.

In New Zealand, nearly half of our greenhouse gas emissions – mostly methane and nitrous oxides – come from livestock and fertiliser use.