Predicting the new normal

This article first appeared in The Listener, 26 November 2015.

“Climate prediction is not an easy job anywhere,” says Dave Frame, professor of climate change at Victoria University of Wellington, but “the southern hemisphere hasn’t generally been the focus for the world’s largest modelling initiatives, partly because the incentives are always to improve simulation near where taxpayers live.”

Frame is director of the Deep South National Science Challenge, a ­$24-million project that aims to help this country “adapt and thrive” under whatever climate lies in store. He says existing models, good at predicting average global temperature rises, don’t do well when it comes to predicting conditions in New Zealand. The challenge’s goal is to develop a numerical earth system model to simulate this country’s current and possible future climates.

Even under the best-case scenario being debated at December’s COP21 meeting, which would avert extremes of temperature increase and sea-level rise, there will still be a certain amount of climate change.

Deep South hopes to develop a better understanding of the climate processes that control New Zealand conditions. On November 25, the challenge announced $9 million of funding for projects that include observing Antarctic sea ice, assessing the effects of clouds and aerosols, analysing pre-Industrial weather observations from the 1800s and determining the effect of the recovering ozone hole.

“In the southern part of the southern hemisphere, recovery from the ozone hole is a really significant feature of our climate – it’s broadly comparable with the greenhouse signal,” says Frame.

A better model will help Deep South improve predictions of extreme weather, droughts, changes in growing conditions and sea-level rise. In a planned second phase, Deep South hopes to “help people plan for the future, so it’s an integrated modelling and adaptation project”.

One of the tools to be used alongside the new model is weather@home, a crowd-sourced climate-modelling experiment that uses personal computers to run thousands of weather simulations and provide hard numbers on how climate change might affect the risk of extreme events. (To sign up, go to climateprediction.net.)

A recent paper, published in the Bulletin of the American Meteorological Society and led by Niwa climate scientist Suzanne Rosier, shows the odds of an event such as July 2014’s damaging Northland floods have doubled since pre-Industrial times.

“This project aims to get a handle on the new normal: if it’s happening twice as often now, when will it start to happen three times as often?” says Frame. “Deep South is primarily a model-based initiative – modelling is the only way to coherently assess a broad range of influences.”

For example, the expansion and collapse of Antarctic sea ice – the continent essentially doubles in size each winter – is one of the biggest annual geophysical changes on the planet. It plays a significant role in influencing our weather systems. Satellite observations show the maximum extent of sea ice around Antarctica has increased over the past three decades, which seems at odds with global warming. Earth system models used now can’t reproduce this increase in sea ice. A model that does will require a better understanding of the processes involved.

In work that will aid the Deep South challenge, Niwa’s Craig Stevens led a team that studied the sea ice for three weeks in October. The researchers observed turbulent heat and energy-exchange processes between the ocean and the sea ice.

Stevens says, “We have three or four different ways of measuring turbulence and the same number of ways of measuring the heat structure in the upper part of the ocean and the lower part of the ice.” At the research site – 25km west of Scott Base – they encountered a 2m-thick layer of ice crystals along with 2.5m of sea ice. Their work measures how these crystals dramatically change the nature of ice-ocean interaction.

Over the course of the challenge, a sea ice project led by University of Otago’s Pat Langhorne hopes to connect Stevens’ field-based observations with airborne detection methods to determine how to better estimate sea-ice thickness, along with any associated ice crystal layer, by satellite.

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About Rebecca Priestley

I have a PhD in the history & philosophy of science and I write about science and science history. I live in New Zealand.
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