Climate Changed: How a warming world has already transformed NZ

Newspaper Published Source
The New Zealand Herald 2020-10-14 Link

The devastation at Lake Ohau has given us a glimpse of the damage wildfires can do - and climate projections tell us that's only going to get worse. Photo / Otago Daily Times Science Reporter Climate change isn't just a crisis of our future, but our present - and that's been made unequivocally clear by a new Government report revealing a rapidly transforming New Zealand. Science reporter Jamie Morton looks at five of the most glaring facts. Our climate is warming, and quickly. That's the first obvious takeaway from the Our atmosphere and climate 2020 report, just released by Stats NZ and the Ministry for the Environment. Of 30 sites analysed around the country, since 1972, the annual average temperature has climbed at 28 of them over summer - and across all in winter. In Nelson, that average has climbed by about 0.29C per decade - and similarly big increases have been recorded at Reefton and Tara Hills in inland Canterbury. Eighteen of the 30 sites have also seen a very likely increasing trend in the number of "heatwave days", which come in stretches when maximum temperatures reach more than 5C above the monthly average. Again, some of the fastest increases have been at inland South Island spots like the Tara Hills, Lake Tekapo and Queenstown - with all seeing several more days of these hot conditions each decade. Added to that is the fact that the number of frost days has likely been dropping at nearly half of the 30 spots, while the frequency of drought has been increasing at 13. Some of the fastest falls in frost days have been registered at Nelson and Tara Hills, which have been losing an average five of these chilly days each decade. And some sites that already rarely experienced frost days now no longer experience them at all. Whangarei hasn't seen a sub-zero temperature since 1994. The number of "warm days" - where the max reaches above 25C - has meanwhile increased at 19 of the sites, but notably at Masterton, Reefton and Tauranga. Last year, the annual average land-surface temperature in New Zealand was the fourth highest since records began, way back in 1909. Over 111 years, that average has risen by about 1.13C. The starkest changes have come in the past 20 years, of which 16 were "above average" compared with the 1961-1990 baseline. Overall, New Zealand's national average temperature has increased by 0.10C per decade since 1909 - but that rate has quickened to 0.31C per decade in the past 30 years. Some regions have been getting drier under climate change - and others wetter. A third of places, many of them in the northern North Island, have recorded less rain, while spots in the south and west of the South Island have seen more. For instance, annual rainfall has shrunk by an average 4.3 per cent per decade in Whangarei, and by 3.2 per cent in Tauranga. But it's been increasing by 2.8 per cent per decade in Whanganui, by 2.1 per cent in Milford Sound, and 1.3 per cent per decade in Hokitika. Changes in rainfall haven't happened evenly across the year and it's been over spring, especially, that most of the sites have recorded shifts. Most places with increasing rainfall have also had more "intense" rainfall, where it's fallen in a shorter period of time rather than being spread out over the year. As for "extreme" rainfall, the report found a longer record of data was needed to pick out trends. Meanwhile, New Zealand's growing seasons have slowly been stretching out. The report looked at "growing degree days", which are used to estimate the length of the growing season for agriculture and horticulture. This measure counts the total number of degrees that the average temperature is above a base temperature - typically 10C - each day. Since the early 1970s, nearly all of the 30 spots have seen an increasing trend. Records taken across a century show New Zealand's mean relative sea level has risen, on average, about 1.81mm each year. Just as with temperatures, most of that shift has come over recent decades: the average rate since 1961 has been twice that of the half-century before. Globally, mean sea level has risen more than 7cm in just 25 years - and much of that has been attributed to melting ice sheets in Greenland and Antarctica. But New Zealand's coastal seas aren't just rising - they're also warming, by a rate of 0.2C per decade since the start of the 1980s, and notably off the South Island's west coast, and east of Wairarapa's coast. Studies indicate that just a small amount of sea-surface warming is needed to affect the stability of ice shelves in Antarctica, which may lead to multi-metre rises in sea level over coming centuries. Higher concentrations of carbon dioxide in the air is also making oceans more acidic, hurting species like corals and shellfish. In just two decades, the subantarctic waters off the coast of Otago became 7 per cent more acidic. Warmer coastal waters have also been blamed for recent melt of New Zealand's picturesque glaciers. In 1997, the volume of ice in these alpine wonders peaked - but by just two decades later, around 28 per cent of the ice had vanishing, losing enough to fill Wellington Harbour 12 times. During an unprecedented "marine heatwave" in the record-hot summer of 2017–18, the Southern Alps lost about 3.8 cubic km of glacier ice - the largest amount in a single year since 1962. New research has linked years with the highest levels of ice loss to man-made emissions, finding that global warming made the extreme ice loss observed in 2018 at least 10 times more likely. Evidence gathered from sediment and ice suggests it's been about 10,000 years since the average annual temperature was as high as it is today. Those temperatures we're now feeling are therefore likely to be near the top of the range that current ecosystems have experienced. In some cases, it's been too much to bear: the 2017-18 marine heatwave led to a complete loss of rimurapa, or bull kelp, at reefs in Lyttelton and other places. A changing climate can make other pressures worse. On Otago Peninsula, a study found that warming seas contributed to a drop in the survival rates of hoiho, or yellow-eyed penguins – probably by reducing the number and size of the fish they feed on. In Horowhenua, Ngāti Raukawa ki te tonga have noticed a decline in eels, one of their most prized taonga. Research points to climate change impacts on ocean currents and the tuna's food chain, as well as changes to its habitat, as affecting the species' sensitive life cycle. In the future, a warmer climate might cause some native fish species to be lost from places they once inhabited. Alpine galaxias are native to mountain streams but are sensitive to temperature and can't live in water that is too warm. In the Waikato River, inanga - an iconic species caught as whitebait - have been found to be smaller in spring and summer when the water is warmer. Rising temperatures are also limiting where our species can live. Early signs include two weta species moving to higher elevations on Mt Taranaki. Many native birds have already retreated into cooler parts of their former habitats because there are more predators like possums, rats, and stoats in warmer lowland forests. As the area of cooler forests shrinks, that pressure from predators will increase further - especially on large birds like kiwi, whio and North Island kokako that can't easily move. Added to the threat to our biodiversity are knock-on blows from extreme weather. Droughts have shrunk the body size of the critically-endangered Canterbury mudfish, and flooding in 2009 wiped out 84 per cent of a high country population of scree skinks. The devastation at Lake Ohau has given us a glimpse of the damage wildfires can do - and projections tell us that's only going to get worse. By 2040, days with very high or extreme fire danger are projected to increase by an average of 70 per cent, due to hotter, drier and windier conditions. And the largest increases are projected for areas that are not used to fire. Wellington would experience a doubling to 30 days a year and coastal Otago a tripling to 20 days a year. If global emissions continue to increase, by 2090, warm days – where the maximum temperature is 25C or higher – are projected to occur four times as often in Auckland. Even if emissions are reduced to limit global warming below 2C, these days would still increase by 55 per cent. And research suggests that when temperature climbs above 20C in Christchurch and Auckland, up to 14 heat-related deaths happen each year among over 65-year-olds. So, where are we at with our climate pollution? New Zealand's own net emissions shot up by 57 per cent from 1990 to 2018. Three years ago, the 7.7 tonnes of CO2 that each Kiwi pumped into the atmosphere put New Zealand at 17th out of 32 OECD countries for emissions. Our largest source of CO2 emissions come from road transport - utes and SUVs particularly use more fuel - and we effectively import emissions when we use goods and services from overseas. But most of New Zealand's greenhouse gases still stem from agriculture. Methane - mainly burped from livestock - made up nearly half of our gross emissions in 2018. Globally, emissions are expected to keep rising. At the current rate, the global average temperature is likely to cross the threshold of 1.5C above the pre-industrial level within the next 10 to 30 years. And a rise of 3C by the end of this century is projected, even if all the current emissions reduction commitments and goals are met by the international community. Deep cuts to net emissions would be needed to hold warming to 1.5C - about 45 per cent below 2010 levels by 2030, and net zero by about 2050. In New Zealand, greenhouse gas emissions are projected to decrease in the coming decades under existing policies, but not at a fast enough rate to meet our 2030 goals under the Paris Agreement. As today's report states, "profound changes" to our climate are expected. "Higher temperatures are expected across New Zealand, with drought and wildfire risk projected to increase in many places," it says. "What were rare, extreme events for us may become common for our children and grandchildren."