Disappearing frosts a concern for agriculture

13 August 2007Stuff.cod.nzMatt Calman

A decline in frosts was one of the most noticeable signs of climate change and could pose problems for agriculture, said Niwa scientist Jim Renwick.

"(Frost) tells things like fruit trees that they need to get ready to bud in the spring. They need to have winter chilling to do their whole life cycle properly, and a lot of animal and plant pests die off in winter because they get frosted.

"If that doesn't happen then that makes it a lot easier for a lot of pests - especially subtropical species - to survive in New Zealand."

Since the 1950s there has been an average of three fewer frost days per decade. In South Island areas and at higher elevations the decline has been closer to 10 to 15 days per decade.

A decline of three days in 10 years did not sound much, but if the rate of climate change continued it would become more significant, Dr Renwick said.

"In another 50 years if we get a further degree of warming, which is what's expected, then you might see quite a decrease in the number of frosts.

"In a lot of the low-lying parts of the North Island I would expect frosts to be unknown by later this century," Dr Renwick said.

When he gave public talks, older people told him they could remember icy winters, but their children and grandchildren did not have the same experiences.