The evidence of climate change

The evidence of climate change

(Image:Kuno Shweitzwer : Tasman glacier lake)

New Zealand’s disappearing glaciers

Summary

“You can’t make a glacier lie.” – Dr Andrew Lorrey; NIWA

  • NIWA has carried out aerial surveys of over 50 of the South Island’s glaciers every year for more than 40 years.
  • One-third of New Zealand’s glacial mass was lost between 1977-2017
  • New Zealand’s glaciers have all retreated and lost volume since NIWA started surveying them in 1977.
  • The large losses in 20118 and 2018 loss have been directly attributed to climate change
  • Glacial lakes form when glaciers retreat; the Tasman glacial lake (photo at top of page) didn’t exist before 1973.
Video 1: The 2018 survey was carried out after New Zealand’s hottest summer on record.

Fig. 1: Instructions for this interactive graph (Credit: The Institute.)

  • Mouse over anywhere on the graph to see the changes in global temperatures over the last thousand years.
  • To see details for time periods of your choice, hold your mouse button down on one section then drag the mouse across a few years, and release it.
  • To see how this compares to the past 771,000 years, click on the ‘time’ icon on the top left.
  • Compare this to rising global temperatures by clicking the planet/thermometer icon at the top left corner.
  • To return the graph to its original position, double-click the time icon to the left of the thermometer/planet icon

Temperatures were warmer 120,000 years ago, however the amount of carbon dioxide in the atmosphere today is much higher. There is a lag time between carbon dioxide concentrations and temperature, so higher temperatures are ‘locked in’ over the coming decades.

Glaciers grow when more snow accumulates than melts. Conversely, they shrink when more snow melts that accumulates. Sometimes weather patterns like El Niño/La Nina can lead to warmer weather, and there’s a usually a lag time between the loss and the glacier retreating. So how do we know if the decline of New Zealand’s glaciers isn’t just a temporary or localised change?

The planet has already warmed more than 1°C since pre-Industrial times (Fig. 1), and this has led to a long term trend in glaciers all over the world shrinking or even disappearing.

Here in New Zealand, we have around 3,000 glaciers, most of which are found in the Southern Alps (Fig. 2). NIWA has carried out aerial surveys of over 50 of the South Island’s glaciers every year for more than 40 years, and the trend has been one of ongoing loss of ice mass:

“When I started this in 1977, we had 53 cubic kilometres of ice. Today (2017) we have 30% less…. The glacier is the best climate indicator you can use. There’s everything in the climate that changes the volume in a glacier.” – Dr. Trevor Chinn / NIWA  (Video 1).

In spite of 2018 being a very weak El Niño year, New Zealand experienced its hottest year on record:

“During austral [southern hemisphere] summer 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 +2.2 °C, and sea surface temperature anomalies reached +3.7 °C in the eastern 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)… 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.” Salinger et al 2019

This has profound implications for New Zealand as we depend on glaciers for renewable energy (hydropower) and irrigation.

A team from Antarctic Research Centre, Victoria University of Wellington and Monash University in Australia factored in known natural climate forcings and compared them to human climate forcings. Their results conservatively estimate that man-made climate change made the extreme ice loss seen in 2011 at least six times more likely, and the ice loss seen in 2018 at least 10 times more likely. The mass loss recorded from just Brewster’s glacier in 2018 was up to 350 times more likely by climate change.

““The results of our work show that the high melt in 2011 was at least six times more likely to have happened with climate change – but could be as high as 70 times. The high melt in 2018 was at least 10 times more likely to have happened with climate change, or as high as 350 times.

“Extreme glacier melt events will increase in frequency and severity, especially as extreme heatwaves and marine heatwaves increase in frequency and severity. In fact, since we completed the study, New Zealand glacier melt measured in 2019 was almost as high as the melt in 2018 – and higher than in 2011.” –  Dr Lauren Vargo,Antarctic Research Centre, Victoria University of Wellington

Fig. 2: The main glaciers in the South Island (Image: Chinn et al.)
Fig. 3: Changes in ocean temperatures around New Zealand 2010 – 2019 (Image: NIWA). Warmer oceans means there’s more water vapour over the water. And warmer air can carry more moisture. This powers tropical cyclones, so they may reach New Zealand more often, bringing greater risks of destructive winds and flooding.
Fig: 4: Eight-year-old resting on a rock close to the glacier terminus. (Image: Whitelaw)
Fig: 4: Eight-year-old resting on a rock close to the glacier terminus. (Image: Whitelaw)
Fig: 5: Eighteen-year-old (same person) a decade later.  (Image: Whitelaw)
Fig: 5: Eighteen-year-old (same person) a decade later. (Image: Whitelaw)

References and further reading