Respirations
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Hi I'm Bryan Yeaton and this is The Weather Notebook.

The leaves of plants use the process of photosynthesis to take carbon, from carbon dioxide, out of the air, but all plants also release some carbon dioxide back into the air,. It's a process known as "respiration".

Carbon in and carbon out - that's a delicate balance that must be maintained. As Weather Notebook correspondent Allan Coukell reports, it's a balance that could be tipped by global warming.

WHITEHEAD: Here we are in the tops of these rimu trees.

COUKELL: David Whitehead is a scientist with Landcare Research in New Zealand. I followed him up a series of ladders into the treetops to learn what effect global warming will have on this forest.

WHITEHEAD : The temperature is increasing, and in particularly night temperature. And in the last decade the increase has really increased, as it were. It's really stepped up.

COUKELL: Plants grow by taking in carbon through photosynthesis in their leaves, but they also release carbon through respiration, just as you and I do when we exhale. If a tree is going to grow, the carbon that comes in through the leaves has to exceed the carbon dioxide going back out again.

But David Whitehead says that warm temperatures increase respiration more than photosynthesis, and that's bad news for the growth of the forest.

WHITEHEAD: Respiration is affected by temperature much more than carbon dioxide uptake, and so the question is "is the carbon balance - we call it the carbon balance, the net intake minus loss of carbon - is it going to change in a forest like this?" And if it were to change, we such that the of carbon exceeded the incoming of carbon, we would possibly see a gradual decline in these forests.

COUKELL: Up in the tops of the trees scientists are also studying the effects of changes in cloud cover and rainfall.

That's correspondent Allan Coukell of Auckland, New Zealand.