Climate change and climate sceptics

OPINION: As the un-named tobacco executive said decades ago, when faced with hard scientific evidence of the link between smoking and cancer: "Doubt is our product since it is the best means of competing with the 'body of fact' that exists in the mind of the general public."

That tactic has been tried and tested many times, to throw doubt on smoking and cancer, air pollution and acid rain, CFCs and the ozone hole, and more recently fossil fuel burning and climate change.

The excellent book Merchants of Doubt by Naomi Oreskes and Eric Conway documents in great detail how this has been done and how successful it has been over the years.

In his recent op-ed piece Doug Edmeades is clearly looking to sow seeds of doubt, to undermine established science, and to argue that there's nothing to worry about. He seems to understand the idea that "doubt is our product".

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The science on climate change really is solid – "unequivocal" was the word used in the summary of the last Assessment Report of the Intergovernmental Panel on Climate Change (IPCC).

We know how the climate is changing, why it is changing, how it relates to past changes, and what the future holds.

About the only way to argue against the findings of decades of research by thousands of scientists is to ignore the evidence and to claim that our understanding of climate change is "just a hypothesis".

So what do we actually know about climate change?

Information from the laboratory, from basic physics, and from measurements in the field tell us that there are just two ways to change the climate.

Either change the brightness of the sun, or change the amount of greenhouse gas in the air.

Those are the only two things that regulate the amount of heat at the earth's surface. They explain all the ice ages and other changes in the past, and they explain the present changes we see. They can work together (as in the ice ages) or one can act independently (as in today's climate changes).

The greenhouse gases are important because they soak up the heat the earth radiates, just like a duvet on your bed soaks up the heat your body radiates. The duvet keeps your body warmer, and the greenhouse gases keep the earth warmer.

Adding greenhouse gases to the air is like putting a thicker duvet on your bed – what's underneath gets warmer.

In the past 70 years, the sun hasn't brightened up, in fact it's become a bit dimmer recently. Meanwhile, the concentration of carbon dioxide in the air has gone up over 40 per cent since we started burning oil and coal for fuel, the biggest change in the Earth's atmosphere for over 3 million years.

We know the increase is down to us burning fossil fuels, because the chemical signature of fossil carbon is different, having lost its radioactive fraction over millions of years underground.

Plus, the amount of oxygen in the air is going down as carbon dioxide goes up, a sure sign of burning.

Human activity, mostly burning fossil fuels, is the only explanation for the way the atmosphere is changing, and how that is changing the climate.

And the climate is clearly changing, as recent heatwaves, wildfires, flooding rains, and coastal inundation attest.

The idea that there has been no warming in the past 20 years is just wrong, even in the "satellite record" the sceptics love.

Twenty years ago there was a big El Niño, making 1998 a very warm year globally. So naturally if you start from 1998, the warming trend seems smaller.

This is a classic example of "cherry-picking", choosing just the numbers that suit your argument and ignoring the rest.

The full satellite temperature record, and the ground-level thermometer record, the ocean temperature record, the sea level record, and the ice-melt record all tell the same story of significant warming, over the past 20 years, 50 years, 100 years.

It lines up exactly with that ever-thicker duvet we're draping over the globe.

The Earth is already over 1 degree Celsius warmer than it was in the 19th Century, heading for 2°C warmer if we're lucky and 4-5C if we're not. The difference in global temperature between an ice age and today's climate is only 5-6C, so a couple of degrees is huge.

As water warms, it expands, so sea levels have been rising for over 200 years. Add in the ever-increasing melt of glaciers and the big ice sheets and we see an acceleration.

Today, sea levels are rising around twice as fast as they were a century ago, and are set to rise much faster as Antarctic and Greenland ice melt really gets into gear.

Because beaches are pretty flat, even 10cm of sea level rise can push the high tide mark inland quite a way.

How much longer coastal properties can get insurance is an open question.

The way we experience climate change and sea level rise is through extreme events.

In New Zealand the past year has seen several big floods, coastal inundation around the Coromandel and Auckland, temperatures over 30C in Southland for several days in a row, droughts and wildfires.

As the climate warms, it becomes easier to get extreme high temperatures. They dry soils faster, making droughts easier to come by.

Warmer air holds more moisture, so it becomes easier to have heavy rainfall when there's a storm.

Higher sea levels make it that much easier for a storm surge to damage coastal property. Not every extreme is due to climate change, but the changing climate just makes it easier and easier to have such extremes.

The best source of information on climate change is the Intergovernmental Panel on Climate Change (IPCC) which summarises the science every few years.

Extreme events are an important focus – in 2012 the IPCC published a special 500-page report on exactly this, citing hundreds of studies that show climate change is leading to increasing extreme events.

How Doug Edmeades thinks that the IPCC says there's no connection between the two is a mystery to me.

Doug Edmeades' other ideas (polar bears are doing great, models are no good, and so on) are easily shown to be false with a bit of googling.

None of us want the sorts of disruptions that the changing climate is bringing. But, if we are to get on top of this biggest of problems, we must get our heads around the fact that after thousands of years of stability, things are changing, sea levels are rising, and we must respond.

I hope the governments, businesses, and societies of the world can fast-forward that response, starting right now.

- Dr James Renwick is Professor of Physical Geography at Victoria University. He has about 30 years' experience in weather and climate research, and was involved in writing the IPCC fourth and fifth assessment reports.

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