Farmed Fish Dying, Grape Harvest Weeks Early Are Just Some Of The Effects Of Last Summer's Heatwave In NZ
Queensland groper, typical of coral reefs off Queensland at 27°S were found in the Bay of Islands, north of Auckland, at 35°S. from www.shutterstock.com, CC BY-ND
As the Australian heatwave is spilling across the Tasman and pushing up temperatures in New Zealand, we take a look at the conditions that caused a similar event last year and the impacts it had.
Last summer’s heatwave gave New Zealand its warmest summer and the warmest January on record. It covered an area of four million square kilometres (comparable to the Indian subcontinent), including the land, the eastern Tasman Sea and the Pacific east of New Zealand to the Chatham Islands.
In our research, we looked at what happened and why, and found that the heatwave affected many sectors, leading to early grape harvests and killing farmed fish in parts of the country.
Drivers of warmer than average conditions
We used a combination of land and ocean temperature observations, large-scale analyses of the atmospheric circulation, and ocean modelling to understand the drivers of the 2017/18 summer heatwave. It was memorable for a number of extreme events and statistics.
The average air temperature was 2.2°C above the 1981-2010 normal of 16.7°C, and it was the warmest summer ever recorded in more than 150 years. The number of extreme warm days and warm nights was also the highest recorded, going back several decades.
The peak month was January 2018, 3.2°C above normal and the warmest month recorded in observations as far back as 1867. Ocean surface temperatures were similarly extreme, with a marine heatwave that lasted about five months, at 2.0°C above normal at its peak.
Jim Salinger, CC BY-ND
The warming was mostly the result of very settled conditions over the country, especially to the east, bringing light winds, plenty of sun, and warm air from the subtropics. Such conditions in summer are associated with the positive phase of a polar ring of climate variability known as the Southern Annular Mode (SAM), which brings high pressures (anticyclones) to New Zealand and parts of other southern hemisphere countries in the mid-latitudes, including southern Australia and Tasmania, southern Chile and Argentina.
The SAM was strongly positive throughout last summer, especially in January, and weak La Niña conditions were prevalent in the tropics. The light winds in the New Zealand region allowed the ocean surface to warm rapidly, without the usual turbulent mixing to transport the heat away. The warmest waters in the Tasman Sea formed an unusually thin layer near the surface.
Impacts and repercussions
New Zealand was affected by more than its normal share of ex-tropical cyclones, notably Fehi and Gita. They brought strong winds, storm surges and heavy rainfalls that caused flooding as they passed through. The warm ocean waters around New Zealand would have helped maintain the intensity of the storms and supply moisture to drive the heavy downpours.
The warm conditions caused massive ice loss in South Island glaciers, estimated to be the largest annual loss of glacier ice in nearly 60 years of records for the Southern Alps. Satellite data from end-of-summer snowline measurements at the Tasman Glacier suggest that the Southern Alps lost 9% of glacier ice during last summer alone.
Warm air temperatures had a marked effect on managed and natural ecosystems. The Marlborough grape harvest was unusually early in 2018, two to three weeks ahead of the normal maturation time. Marine ecosystems were significantly disrupted. Coastal kelp forests struggled to grow in the warm sea. In southern New Zealand, the temperature threshold was breached three times, resulting in substantial losses of kelp canopies.
For the first time, Atlantic salmon had to be imported as farmed fish died in salmon farms in the Marlborough Sounds. Commercial fishers reported that snapper was spawning approximately six weeks early off the South Island coast, and Queensland groper was reported in northern New Zealand, 3000km out of range.
Past and future
The summer of 2017/18 shared some characteristics with another hot summer, way back in 1934/35. That season was so warm that it prompted a special report by the New Zealand Meteorological Service. Conditions were similar: persistent high-pressure systems in the New Zealand region, positive SAM conditions, light winds over and around New Zealand, warm ocean surface and air temperatures. While those two summers shared some natural variations in the local climate, the recent summer was warmer for two reasons.
First, climate in the region is now more than half a degree warmer now than in the 1930s. Second, the SAM has been trending towards its positive phase over the last few decades, making settled conditions over New Zealand more frequent now than in the 1930s. That trend is mostly related to the ozone hole that occurs in spring and early summer, cooling the polar atmosphere and driving the strongest winds farther south towards Antarctica, leaving lighter winds and higher pressures over New Zealand.
Looking to the future, we can compare the conditions experienced in 2017/18 with what climate models predict for the future. We estimate that the extreme warm conditions of New Zealand’s last summer would be typical summer conditions by the end of the century, for an emissions scenario associated with a couple of degrees of global warming above pre-industrial temperatures. If emissions keep increasing as they have done in recent years, last summer will seem cool by the standards of 2100.
About The Author
Jim Salinger, Honorary Associate, Tasmanian Institute for Agriculture, University of Tasmania and James Renwick, Professor, Physical Geography (climate science), Victoria University of Wellington
Life After Carbon: The Next Global Transformation of Cities
by Peter Plastrik , John Cleveland
The future of our cities is not what it used to be. The modern-city model that took hold globally in the twentieth century has outlived its usefulness. It cannot solve the problems it helped to create—especially global warming. Fortunately, a new model for urban development is emerging in cities to aggressively tackle the realities of climate change. It transforms the way cities design and use physical space, generate economic wealth, consume and dispose of resources, exploit and sustain the natural ecosystems, and prepare for the future. Available On Amazon
by Elizabeth Kolbert
Over the last half-billion years, there have been Five mass extinctions, when the diversity of life on earth suddenly and dramatically contracted. Scientists around the world are currently monitoring the sixth extinction, predicted to be the most devastating extinction event since the asteroid impact that wiped out the dinosaurs. This time around, the cataclysm is us. In prose that is at once frank, entertaining, and deeply informed, New Yorker writer Elizabeth Kolbert tells us why and how human beings have altered life on the planet in a way no species has before. Interweaving research in half a dozen disciplines, descriptions of the fascinating species that have already been lost, and the history of extinction as a concept, Kolbert provides a moving and comprehensive account of the disappearances occurring before our very eyes. She shows that the sixth extinction is likely to be mankind's most lasting legacy, compelling us to rethink the fundamental question of what it means to be human. Available On Amazon
Climate Wars: The Fight for Survival as the World Overheats
by Gwynne Dyer
Waves of climate refugees. Dozens of failed states. All-out war. From one of the world’s great geopolitical analysts comes a terrifying glimpse of the strategic realities of the near future, when climate change drives the world’s powers towards the cut-throat politics of survival. Prescient and unflinching, Climate Wars will be one of the most important books of the coming years. Read it and find out what we’re heading for. Available On Amazon
From The Publisher:
Purchases on Amazon go to defray the cost of bringing you InnerSelf.comelf.com, MightyNatural.com, and ClimateImpactNews.com at no cost and without advertisers that track your browsing habits. Even if you click on a link but don't buy these selected products, anything else you buy in that same visit on Amazon pays us a small commission. There is no additional cost to you, so please contribute to the effort. You can also use this link to use to Amazon at any time so you can help support our efforts.