A tale of two hemispheres

Jim RenwickAt the end of June, Professor Jim Renwick of Victoria University gave his inaugural lecture. As you might expect of a climate scientist, it concerns what we know about the climate system and where we’re heading. He pulls no punches. Jim has been kind enough to put together a text version of the lecture for Hot Topic: it follows. You can watch the full lecture, with accompanying slides, on the video embedded at the end of the post.

We live in a golden age of earth observation. With a few clicks of a mouse on a web browser, any of us can see the state of the global ocean surface, the current condition of the Greenland ice sheet, how much rain is falling in the tropics today, and on and on. Plus, the International Space Station (ISS), and a series of satellites such as MODIS give us wonderful images of our home planet. The climate science community can tell, with unprecedented coverage and timeliness, just what is going on in the climate system. It is a great time to be a climate researcher, but also a worrying time, in both cases because we can see exactly what is changing.

One thing the ISS pictures emphasise is just how thin the atmosphere is, a thin blue layer between the solid earth and the blackness of space. Not only is this life-supporting envelope very thin, some of the key gases in the atmosphere are there in only trace amounts, so we can change the properties of the atmosphere easily, by targeting the right gases. The discovery of the ozone hole 30 years ago brought this home with a bang. And we’ve found that build-up of carbon dioxide (CO2) in the atmosphere can have a profound effect on the climate system, right down to the bottom of the oceans.

Carbon dioxide is important because it’s a crucial control on the surface temperature of the earth. It is very good at absorbing heat (infrared radiation) welling up from the earth, then re-radiating both up and down, in the process warming the earth’s surface. The effect is very like a blanket put on a bed – what’s under the blanket warms up. More CO2 is like putting another blanket on the bed and less is like taking away a blanket. No CO2 and the earth freezes – temperatures like we had in the South Island in late June would be the norm everywhere, all the time. While there are several other “greenhouse gases”, carbon dioxide is the most important since it stays in the atmosphere so long, hundreds to thousands of years.
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Blink and its gone – spectacular time-lapse of ice retreat at Fox Glacier

This spectacular time-lapse video1 captures the dramatic retreat of the Fox Glacier in Westland over the last year — 300 metres between January 2015 and January this year. As the ice retreats, the hillside becomes unstable and collapses down into the valley. To get a sense of the scale, you can see people watching from a safe point on the bottom right.

The rapid retreat of both Fox and its neighbour Franz Josef has led to the abandonment of guided walks on the glacier tongues. The ice is now only accessible by helicopter on to the upper reaches.

The collapse of the walls of the valley at Fox (as well as rocks and sediment transported by the ice) has caused the valley floor to rise by a metre over the last two years, as measured by Massey University scientists (see also NZ Herald). They’ve also photographed the retreat over the last decade, but the most marked loss seems to be in the last few years.

NZ’s west coast glaciers are amongst the most dynamic in the world, fed by huge snowfalls in their nevées under Mt Cook — as much as 6 metres a year in the snowfield feeding the Franz-Josef, as Mauri Pelto notes here. At the moment, ice melt in the tongues of both glaciers is outpacing the ice input above, and so the glaciers are retreating fast, but a run of years with heavy snowfalls could reverse the process — at least temporarily.

  1. Created by Victoria University of Wellington with the support of Fox Glacier Guides, Department of Conservation, Snowgrass Solutions, University of Canterbury and the Marsden Fund. []

Climate documentary Thin Ice raising money for US broadcast

Thin Ice, the superb documentary about climate science and scientists filmed and produced by New Zealand and British climate scientists, has launched a Kickstarter crowdfunding campaign to finance a new edit of the film so that it can be shown on public TV in the US. From the Kickstarter page:

Why do we need help? The global screening on Earth Day, 2013, reached over 200 locations worldwide, and many others have seen it since. Now we have a chance to re-edit the film for screening on American Public Television – if we can raise the NZ$27,500 (US$22,000) in 30 days needed for the re-edit and promotion.

We want the film to be seen by as many people as possible on TV in Europe, Asia, Africa and South America. We already have subtitles in 8 languages, so with the shortened film Thin Ice will be that much more accessible to schools and communities worldwide.

With 14 days to go, the project still needs to raise NZ$20,000, so if you can spare a few dollars go to Kickstarter, make a few climate scientists happy, and help to get this excellent film put in front of a wider audience.

Thin Ice: what polar science is telling us about climate

This guest post is by professor Peter Barrett, executive producer, and Suze Keith, marketing advisor for Thin Ice.

Scientists can tell human stories about climate change, and a group of us have been working on just that for the last few years. We’ve produced a film — Thin Ice – the inside story of climate change — which follows a scientist, geologist and camera buff Simon Lamb, who is concerned at the flak his climate science colleagues have been taking.

Simon travels from the Antarctic to the Arctic. He listens to scientists talk about their work, hopes and fears, and discovers how the astonishing range of research really does fit together. By the end there are just two messages – that our ultimate goal should be zero carbon emissions (in line with the latest IPCC report), and that science really does work. As paleoclimatologist Dave Harwood says to young people at the end of the film:

Don’t be scared by this thing. Come and join in our effort. Be the best scientists and engineers you can, and we’ll deal with it.

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The big warm: NZ heading for warmest-ever winter

If you think it’s been a warm winter in New Zealand, you’re right. NZ is rapidly approaching the end of a record-breaking winter — the warmest for at least 150 years1. Calculations by Auckland climate scientist Jim Salinger show that NZ’s average temperature for June/July/August is running at 9.5ºC, a remarkable 1.2 deg C above the 1971-2000 average, and comfortably ahead of 1998’s old record of 9.3ºC. Commenting on the numbers, Salinger notes the absence of cold snaps in recent months:

The door to cold spells from the Southern Oceans — apart from a brief surge in June — has been well and truly closed this winter. September-like temperatures have been occurring throughout August, giving the country its warmest winter and August ever.

The long term warming signal is clear, he says:

The clearest climate warming signal is seen in winter, where temperatures are now 1.1 deg C warmer than they were around 1870. The warming trends have been very consistent, especially since the 1950s, when frosts days have decreased dramatically across the country.

I can certainly vouch for the absence of frost. At Limestone Hills, we recorded 19 frost days in 2011 and 23 in 20122, but only 6 so far this year. Evidence of winter warmth can be seen in gardens around the country. The asparagus spear pictured above first poked its head out of our soil two weeks ago, and is now being joined by half a dozen more — at least a month earlier than normal for North Canterbury.

To unpick just why this winter’s been so warm, I asked VUW climate scientist Jim Renwick to look back at the atmospheric circulation set-up in the New Zealand region. Here’s his (lightly edited) analysis:

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  1. Reliable temperature records in NZ date back to the 1860s. []
  2. For the full year. Frost days are any day where the temp falls below zero, and are unusual (1 – 2 a year) after August. []