Carbon dioxide makes the largest contribution to global warming and climate change. Forests are highly effective at capturing carbon from the atmosphere and make great carbon sinks. Forests capture carbon, whereas most other human activities emit carbon - See Figure 1.

Forests have been decreasing in area as a result of man's activity. Forests covered 80% of New Zealand before the arrival of Maori, and 50% when Europeans began their major immigration in 1840. Forests now comprise only 24% of New Zealand's land area - See Figure 2.

A cubic metre of wood contains about 250 kg of carbon (250 000 grams), while a cubic metre of air contains about 0.117 grams of carbon. This means that a cubic metre of wood contains the same amount of carbon as 1.4 million cubic metres of air. A forest growing at the rate of 10 cubic meters of wood per hectare per year is absorbing the carbon from 14 million cubic meters of air (a column of air 1400 metres high over one hectare)*.