Uncertain science dogs climate debate
The Government's Energy Strategy aims to reduce carbon emissions from power stations to help reduce man-made greenhouse gases.
Many scientists believe such gases are leading to global climate change and are damaging animal and plant life - and that it will get much worse.
Leading the charge internationally is former United States vice-president Al Gore and his documentary film An Inconvenient Truth.
Climate change could mean more droughts and floods, with temperatures rising by up to 4 degrees celsius by the end of the century, causing ice caps and glaciers to melt.
But in an often bitter debate, sceptics argue the science on climate change is not settled.
Instead, they say international government climate change policies will cost billions to solve a problem that in all probability does not exist.
Kiwi electricity consultant Bryan Leyland recently led a team of international sceptics to a climate conference in Bali.
He maintains the world has not warmed in the past nine years and that the only evidence of global warming is computer models which he calls "junk".
Mr Leyland says the Bali conference was "more about politics than science".
Mr Gore's speech in Bali contained dozens of errors, according to sceptic Viscount Monckton of Brenchley, who was an expert witness in a recent court case in Britain in which a judge ruled that there were nine serious scientific errors in An Inconvenient Truth.
However, Victoria University geologist and Antarctica expert Peter Barrett says the world's best scientists, in the United Nations' Intergovernmental Panel on Climate Change, say the climate is already changing, causing widespread damage to plants and animals.
Professor Barrett, a leader of drilling projects studying the history of Antarctica, says evidence is strong that the main cause of climate change is carbon dioxide, at eight billion tonnes a year and rising, mostly from fossil fuels.
The amount of carbon dioxide is alarming because it is rising above levels last seen three million years ago in the Pliocene "warm period", when sea levels were 25 metres higher than at present, he says.
Professor Barrett says the full effects of higher CO2 will be centuries away, but signs of that eventuality will become more obvious in just a few years.
"If we don't use our brains then we could really run into serious trouble as many civilisations have done in the past.
"We are at a turning point."Though there is often reference to "global warming", Professor Barrett concedes that the whole planet is not warming.
The three main areas are the Arctic sea ice, Siberia and the Antarctic Peninsula, he says.
Since pre-industrial times, global temperatures have risen 0.7C.
Sceptics say the world is actually warmer now than in the so-called Medieval warm period 1000 years ago. They also say that today's temperatures are not unusual or unnatural.
During last summer, as in many other years, Arctic sea ice shrank to worrying levels but returned to normal levels in winter.
But according to some predictions, the area could be ice-free by 2040.
Professor Barrett says that just because summers are warmer, winters are not necessarily warmer as well.
If all the Arctic ice did melt, global sea levels would not necessarily change, he says.
"There is no effect on sea level."
However, a global temperature rise of 2.7C could melt Greenland's 2000-to-3000-metre-thick ice sheet on land and that would raise sea levels by six metres.
"It would take hundreds of years to melt completely - 10 years ago they were saying thousands of years," he says.
And though the Arctic has warmed, Professor Barrett says there is little evidence of climate change affecting the total area of Antarctica.
One relatively small area of the Antarctic Peninsula is at greater risk because it sticks out and is subject to higher wind speeds that warm the ice shelf, Professor Barrett says.
Asked why the Arctic should be showing signs of global warming, but not most of Antarctica yet, he says it might be because of an inertia factor of such a big and cold mass of ice.
"If we can't explain it, we just don't understand the system."
Professor Barrett says the Antarctic is melting about 100 cubic kilometres a year, equal to a sea level rise of about 0.4 of a millimetre a year (plus or minus 0.2mm).
There was huge uncertainty about what would happen to Antarctica in future, and just as much uncertainty about why CO2 and temperatures rose 3C three million years ago.
"We don't know ... The world is a complex place," Professor Barrett says.
The Dominion Post