Some like it hotter
Home » Magazine » Good, issue 3 » Features » Some like it hotterClimate change is here, now, and it’s going to get worse. The numbers may not look big, but they change the face of New Zealand. Gareth Renowden peeks into our warming future, where Wellington’s as warm as Auckland and grapes grow in Gore
A little bit of warming’s a good thing, right? When we’re told New Zealand is expected to warm by about 2°C by the end of the century, it sounds quite attractive. Not so cold in winter, warmer in summer—what’s not to like?
The vineyards of Gore, Canterbury kiwifruit, Nelson avocados, Northland bananas and pineapples … It’s as if New Zealand were floating a bit closer to the equator, the warmth flooding gently down the country from the north.
Take off the rose-tinted sunnies, though, and the picture looks a lot less appealing. That two degrees of warming brings with it a dramatic increase in droughts, extremely hot summers, heavier rain and more flooding, and the possible introduction of tropical pests and diseases.
What we think of as a hot summer today—last summer is a good example—will be normal by the 2040s, and unusually cold by the 2090s. The west coast of both islands will be wetter and the east coasts drier. Sea level will rise, perhaps flooding low-lying land and threatening beach-front baches. Agricultural production will be hit by severe droughts that could happen twice as often as now, and crops will have to move to new regions to follow the climate they like.
When drought bites, the demand for water security will soar—in cities and on farms. Big irrigation schemes like the Central Plains Water plan in Canterbury are already controversial; increased competition for water resources will drive bitter local and regional political battles. We will suffer the economic and social impacts of climate changes that take place in the rest of the world—and they’re likely to be even more severe than we experience here.
This unpleasant picture of New Zealand’s future comes from the latest projections prepared by New Zealand’s Nobel Prize-winning climate scientists at the National Institute for Water and Atmospheric research (NIWA; see box, below).
Bleak as their predictions sound, New Zealand is likely be a lucky country when it comes to the direct impacts of global warming. The big cool southern oceans that surround us will warm more slowly than most places on the planet. It takes a lot of heat to warm up water, and there’s a lot of water in the southern hemisphere, so the sea will moderate the warming we experience.
NIWA’s new projections bear this out. They suggest that New Zealand’s average temperature will warm by about 0.9°C by the 2040s and 2.1°C by the 2090s. The global average temperature increase for the end of the century is 2.8°C, when calculated using the same medium-range carbon emissions scenario. On the continents and at the poles—especially the Arctic—the temperature increase will be much greater than that, and the direct impacts felt more keenly.
The relatively slow pace of change in the Pacific might give us more time to adapt, but it won’t prevent us being affected by what happens overseas (more on that later).
Wetter, dryer, warmer
You could characterise tomorrow’s climate as being like today, only more so. The west of both islands will be wetter, the east will be drier, and the amount of change will increase as the century passes. The extra warmth will bring hotter summers; warmer, shorter winters with fewer frosts; and, where rain is at a premium, the frequency of droughts will increase.
But climate isn’t just a description of the average weather we expect in a given place. It also covers how often big weather events happen.
These weather extremes have huge impacts. Frosts and heatwaves damage crops. Heavy rain erodes gullies and washes topsoil into rivers, causing flood damage as the water rushes to the sea. Intense droughts cause agricultural production to plummet and towns to run out of water. How often those extremes happen, and how bad they are, determine how we are affected by climate change.
You can’t ignore extreme heatwaves, floods and droughts. The good news is, we probably won’t much notice the change in average temperatures.
Our climate is naturally rather variable. The annual average temperature can be as much 1°C warmer in hot years than cool ones, caused by changes in the way oceans move heat around—the familiar El Niño/La Niña cycle, and longer term cycles such as the Interdecadal Pacific Oscillation (IPO).
The IPO, which can stick in one phase for 20 to 30 years, seems to affect the frequency of El Niño and La Niña events. Those have a marked impact on our climate. La Niña (Spanish for “the little girl”) has affected us over the past year or so, tending to warm the country and bring dryness to the South Island. El Niño (“the little boy”) can cool us down and bring drought in the north. The IPO’s current phase seems to make La Niña more likely, so we could be in for a run of hot summers that make it feel like the expected warming’s arriving early.
These up- and down-swings in temperature will be superimposed on a steadily warming trend. We’ll still get hot and cold years, but by the 2040s an ordinary summer will be as warm as the hottest we get now, and a cold year will be one we currently think of as normal.
By the end of the century, even the coolest years will be warmer than a hot year now, and a hot year will be positively Australian. The Waimate wallabies will love it, but the extra heat will be a real challenge to our native plants and animals.
The warming might be gentle from our perspective, but it will be around 20 times faster than when we warmed up after the last ice age. Plant communities will struggle to keep up with the pace, and mountain species might have nowhere left to go. Tropical pests and diseases—salt marsh mosquitoes and dengue fever—could find their way here.
Number crunching
As the years go by, hot summer days will become more common, especially in places that are already warm. Auckland currently averages about 21 days a year when the thermometer gets over 25°C. By the end of the century, that could have increased to more than 60 days, and more than 80 if warming is more severe. Instead of three weeks of hot weather, there could be three months—every year. Great for the bananas in the back garden, but running the air conditioner could get expensive.
Places prone to frost will see a marked reduction in the number of days when temperatures drop below freezing. The high country in the central North Island (excluding the mountains) currently gets around 30 to 40 frost days every year, but that will fall to between five and 15 days by the end of the century.
That all sounds like good news, but what about the rain?
Rainfall is likely to decrease in the north and east of the North Island and down the east coast of the South Island, but it will become wetter in the south and west of the South Island. As the atmosphere warms it’s able to carry more moisture, so storms can carry more ammunition. Heavy rain that happens once in 100 years could happen once every 50 years. Showers could get shorter and sharper. At the same time, drier parts of the country will be experiencing more drought.
NIWA suggests that severe droughts—the sort described today as one-in-20-year events—could be twice as common by the end of the century. For farmers and many small town water supplies, a one-in-20-year drought is a serious event. If it were to happen twice as often, it could be difficult for the farm to recover before the next drought strikes—especially if there are other, less severe droughts in between the big ones.
Warmth will shorten ski seasons, but the extra moisture in the air could mean more snow actually falls, at least on higher slopes. At the moment, most winter precipitation in the catchments of the big hydro schemes in the central South Island falls as snow, so lakes that are low going into winter (like this year) will only begin to fill when the snow melts in spring. More winter rain will do them no harm.
The outlook for our glaciers is not so rosy. The tourist-friendly Franz Josef and Fox glaciers could do well—for a few decades at least—as more snow falls in their nevées, but the ice on the east of the Main Divide will be less lucky. According to NIWA, it will take a period of “extraordinary cooling” to stop the decline of glaciers like the Tasman.
Ice melting in other parts of the world could radically transform our coastline—and the waterfronts in our cities. In the last couple of years, researchers have found large increases in the rate of melting from the great ice sheets of Greenland and West Antarctica. Some scientists now suggest we could see more than one metre of sea level rise by the end of the century, but it’s too early to say just how likely that is.
NIWA’s advice to local authorities is to consider a rise of 80cm by the end of the century. That’s enough to set beaches retreating, estuaries creeping inland, and make high tides and storm surges more damaging.
The luckiest country?
The climate outlook for New Zealand is mixed—good in parts, uncomfortable in others—but we’ll be doing a lot better than the rest of the world. We’re a small country with a relatively small population, and we’re good at growing things. Other places are not so lucky.
In Southeast Asia, hundreds of millions of people living in the great river deltas of Bangladesh, Myanmar, Thailand, Vietnam and China are at risk from relatively modest amounts of sea level rise. If their homes and fields become uninhabitable as the sea encroaches, those millions won’t stay and watch the waves. They will become climate refugees, and that will place a huge strain on the politics and economies of Asia and the world. The peoples of the Pacific islands are already suggesting they will need to move to new homes. New Zealand will be one of them.
In the rich countries of Europe and North America, even modest amounts of warming will bring significant economic hardship. In Spain, which is warming fast, prolonged heat and drought is threatening to turn the southeast of the country into desert, and grape growers are planting new vineyards high on the slopes of the Pyrenees to escape the heat that’s ruining their wines.
What this will mean for life in New Zealand is impossible to predict. Climate refugees both rich and poor might see us as a global warming lifeboat, a place where they can rebuild their lives. Will we let them all in?
If the economies of our key export markets are hit by climate change, the effect on business here will be direct. At the same time, our businesses are vulnerable to what other countries do to limit emissions. Nobody will worry much if by legislating to reduce carbon emissions they make it difficult for New Zealand to sell its goods. Airlines, especially Air New Zealand, are worried that the impact of action on global warming (not to mention high fuel prices) will make it more expensive or plain unfashionable for people to fly long distances. If tourists stop coming, 20 percent of our economy could go down the tubes.
The climate outlook for the next century in New Zealand might be better than in most of the world, but it’s still no picnic. There will be threats, opportunities—and lots to adapt to in the changes we can see coming. The challenges we face will be easier to live with here than in the rest of the world, but what happens everywhere else is going to influence our lives for decades to come.
H2woe
Since the IPPC’s 2007 report there has been a huge amount of new science published, and some remarkable changes in the global climate.
In the Arctic ocean, the summer of 2007 saw a new record minimum for the amount of sea ice—a full 25 percent below the previous record, which was set as recently as 2005. The Arctic summer of 2008 saw that record nearly matched, the collapse of ice sheets off the islands of Canada’s far north, and the opening of the North West Passage in Canada and the Northern sea route off Siberia.
We used to think that the summer sea ice would last well into the second half of the century, but researchers now think it could be gone within a decade—perhaps within years. As the ice disappears, the climate of the whole Arctic is changing rapidly, and it’s more only polar bears suffering. All the land areas around the pole will warm rapidly, and that will have knock-on effects on the climates of Asia, Europe and North America.
The biggest danger is that the loss of the ice will trigger the release of the potent greenhouse gas methane from the vast stores frozen into permafrost and in methane hydrates in the seabed under the East Siberian Shelf. If that happens, global warming will speed up and it will be even more difficult—perhaps impossible—for the world to get climate change under any form of control just by cutting carbon emissions. New Zealand’s slow drift towards the equator will turn into a speedboat ride.
This year’s model
Climate models are hugely complicated computer programmes, designed to reproduce the patterns of weather and climate we see around the world. Feed them with assumptions about how our greenhouse gas emissions are going to rise, and they give us a broad brush picture of how the planet’s atmosphere and oceans will respond.
To produce figures for New Zealand’s possible future climate, NIWA scientists take the output of the global models and look at how they relate to our climate. NIWA’s latest projections take the broad-brush pictures from the Intergovernmental Panel on Climate Change’s Fourth Report, published in 2007, and ‘downscales’ them to New Zealand, providing detail about temperature and rainfall changes by region and season. NIWA’s new regional climate model also provides information about important local effects: the frequency of heavy rainfall events and reduction in frosts.
