Double-digit Temperature Jump Unlikely but Rise Inevitable

Wooden weather Thermometer on black background. Top view.

A projected double-digit rise in the global temperature is unlikely, New Zealand climate change experts agree, but some rise in temperatures is inevitable, they say.

An international research project, reported in Nature, suggested that global mean warning due to greenhouse gases could be as much as 11 degrees Celsius.

However, Dr Jim Renwick, from the National Institute of Water and Atmospheric Research (NIWA), told a Wellington audience recently that an 11-degree rise in temperatures was "outside of the range of what's really expected, at least in the next 100 years."

The Intergovernmental Panel on Climate Change has predicted that, if greenhouse gas levels remain as they are now, then by 2100 average temperatures will be between 1.5 and 5.5C higher than now.

The most realistic scenario, says Professor Peter Barrett, head of Victoria University’s Antarctic Research Centre, is a rise of 3 to 4 degrees. "A 4-degree rise…would take us back to the climate the Earth had 40 million years ago when there was no Antarctic ice sheet," says Professor Barrett.

The Antarctica ice sheet appeared 34 million years ago, when the Earth's temperature started to cool. A 4-degree rise won't see the Antarctic ice melting overnight, says Professor Barrett, but he warned, "it does set it up for disappearing over thousands of years."

Around New Zealand's coastline, the sea level might rise by ½ metre over next 100 years or so, the scientists said.

Dr Renwick pointed out that there were other ways the Earth climate can change: the warming or cooling in the sun can impact on Earth's temperature while volcanic eruptions such as that of Mt Pinatubo in Indonesia can cool the planet. But any natural changes are now being inexorably outweighed by the impact from greenhouse gases, he suggested. "As greenhouse gas levels increase from here, we'd expect (those greenhouse gas levels) to stand out against natural forcings," Dr Renwick said.

The decisions New Zealand makes "in the next few years", Professor Barrett told the audience, will influence the future climate for several generations to come. And even with changes made now, the impact of the gases being produced now will still linger for thousands of years, explained Dr Katja Riedel from NIWA. "Even if we stop producing now, we still have the effects of the gases that are now around," she explained.

That means, said Helen Plume of New Zealand's Climate Change Office, that New Zealand will have to make choices about how it wants to be supplied with electricity. For instance, argued Murray Ward, a climate change consultant, New Zealand could make more of its biofuel resource: "I think New Zealand has got a lot of potential but lot of work needs to be done in that area," he told the audience.

But that climate change was a reality — and needed to be addressed in all areas of public life — was something that the panel were agreed on.

Dr David Wratt, a principal scientist at NIWA and a member of the Bureau of the Intergovernmental Panel on Climate Change, said that all the evidence "paints a consistent picture that we have had significant warming over the last century."

Said Dr Wratt: "In 50 years time what we think of as a warm year now, we'll think of as an average year."

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