Ahead of Show Your Stripes Day on 21 June raising awareness of climate change, Professor Cate Macinnis-Ng delves into the environmental impacts of our warming winters.
A warm start to winter might seem like good news, but unseasonal weather has serious environmental consequences, says University of Auckland Professor Cate Macinnis-Ng.
Record high temperatures have been recorded this month in Wellington and across much of the country, says Macinnis-Ng, a Professor of Biological Sciences.
“A wide range of natural and human systems are disrupted by this abnormally mild winter weather,” she says.
Many native trees typically have a dormant period during winter, but warmer temperatures can spur unseasonal growth, says Macinnis-Ng.
“Our measurements over the past few years show kauri in Auckland are continuing to grow right through winter.
“Unfortunately, that has negative impacts on their ability to store carbon.
“Warmer weather increases tree respiration rates, so more carbon is released into the atmosphere, creating a pretty alarming climate change spiral.”
More insects from warmer climates are becoming pests in New Zealand, as milder winter weather makes it easier for them to survive here, she says.
“We’re likely to get more exotic wasps, which are harmful to our native insects, birds and reptiles – as well as packing a nasty sting for humans.
“We’re also expecting to see increasing numbers of parasites in sheep and cattle and more insect pests in plantation forests.”
With fewer cold snaps, there’s a higher risk of new invasions of larger mosquitoes, ants, cattle ticks, and exotic pests, such as the Queensland fruit fly, says Macinnis-Ng, who works with the University’s Centre for Climate, Biodiversity and Society – Ngā Ara Whetū.
“The good news is flea infestations are expected to decline in parts of New Zealand that are getting warmer and drier.”
New invasive plants from subtropical regions could become established in New Zealand and existing pest plants could spread further, she says.
New Zealand’s alpine zones are particularly vulnerable to winter warming, because the native plants and wildlife there have adapted to icy conditions, with few predators and competitors, says Macinnis-Ng.
Animal pests, such as rats, stoats and ferrets, could increase in numbers and spread to higher elevations in alpine areas as they grow warmer, a pattern known as “thermal squeeze”, she says.
“We’re concerned about thermal squeeze, because it shrinks the remaining safe spaces left for alpine birds, like the kea and our endangered native rock wren, the tuke.
“So the risk of extinctions rises.”
Macinnis-Ng says the horticulture industry depends on cold winter nights to trigger spring flowering.
Future climates could cause kiwifruit vines and fruit trees, such as apples and avocados, to flower less prolifically and have poor-quality fruit, she says.
“Heat stress reduces the quality and size of crops like potatoes and onions.
“But more tropical crops, like bananas, could begin to flourish here.
“Plant breeding and gene technologies might also help us develop fruit and vegetables that can grow well in a warmer world.”
Macinnis-Ng says more scientific research will be needed to develop solutions to the problems warmer winters cause for native wildlife and primary industries.
“As the climate changes, we’re going to need to find the best ways to adapt to all these impacts on our environment and on our society as a whole,” she says.
Show Your Stripes Day uses graphics with coloured stripes to show how climate change has impacted on temperatures in different parts of the world. Blue shades indicate cooler temperatures, while red shades represent warmer temperatures. The event aims to raise awareness about our warming world.