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Marine heatwave melted glaciers and ripened grapes

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Last summer's marine heatwave kept temperatures on land high, melted the Southern Alps' glaciers more than usual, and caused Marlborough Sauvignon Blanc grapes to mature early. A summary of the event shows that average air temperatures over land were up 2.2C, and might be a good indicator of what a typical Kiwi summer will look like around 2081-2100 under current climate change models.

Journal/conference: Environmental Research Letters

Organisation/s: Victoria University of Wellington, National Institute of Water and Atmospheric Research (NIWA), Plant and Food Research, Lincoln University, University of Otago, University of Haifa, Israel

Funder: Deep South National Science Challenge.

Media Release

From: IOP Science

Abstract

During austral summer (DJF) 2017/18, the New Zealand region experienced an unprecedented coupled ocean-atmosphere heatwave, covering an area of 4 million km2. Regional average air temperature anomalies over land were +2.2ºC, and sea surface temperature anomalies reached +3.7ºC in the eastern Tasman Sea. This paper discusses the event, including atmospheric and oceanic drivers, the role of anthropogenic warming, and terrestrial and marine impacts. The heatwave was associated with very low wind speeds, reducing upper ocean mixing and allowing heat fluxes from the atmosphere to the ocean to cause substantial warming of the stratified surface layers of the Tasman Sea. The event persisted for the entire austral summer resulting in a 3.8±0.6 km3 loss of glacier ice in the Southern Alps (the largest annual loss in records back to 1962), very early Sauvignon Blanc wine-grape maturation in Marlborough, and major species disruption in marine ecosystems. The dominant driver was positive Southern Annular Mode (SAM) conditions, with a smaller contribution from La NiƱa. The long-term trend towards positive SAM conditions, a result of stratospheric ozone depletion and greenhouse gas increase, is thought to have contributed through association with more frequent anticyclonic "blocking" conditions in the New Zealand region and a more poleward average latitude for the Southern Ocean storm track. The unprecedented heatwave provides a good analogue for possible mean conditions in the late 21st century. The best match suggests this extreme summer may be typical of average New Zealand summer climate for 2081-2100, under the RCP4.5 or RCP6.0 scenario.

Attachments:

  • IOP Science
    Web page
    Paper is open access

Expert Reaction

These comments have been collated by the Science Media Centre to provide a variety of expert perspectives on this issue. Feel free to use these quotes in your stories. Views expressed are the personal opinions of the experts named. They do not represent the views of the SMC or any other organisation unless specifically stated.

Dr James Renwick, Professor of Physical Geography, Victoria University of Wellington

The heatwave of 2017/18 affected the New Zealand landmass and the oceans surrounding the country. It brought extreme weather, caused massive ice loss in South Island glaciers, major disruptions for marine species, and a very early grape harvest in Marlborough. It shared some characteristics with another hot summer, way back in 1934/35, with persistent high pressures in the New Zealand region bringing plenty of sunshine and warm air.

Light winds and settled conditions helped ocean surface waters to warm rapidly, without the usual turbulence of the Tasman Sea mixing the warmth away. While summer 2017/18 shared some of the same natural variations in the local climate with 1934/35, the human-induced warming trend, and the ozone-hole induced changes in wind patterns, made the recent event both more intense than the 1934/35 summer, and more likely to occur again in future. The very warm conditions experienced over and around New Zealand last summer would be typical of average conditions here by the end of the century, with a couple of degrees of global warming.

Last updated: 25 Jan 2019 9:10am
Declared conflicts of interest:
None declared.

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