The day once again started early for me, as I hit the road determined to make Woomera in good time – especially given that I intended to do quite a bit of geocaching along the way again. In fact, on this day I found upwards of a dozen caches as I travelled along. One of the reasons I enjoy geocaching (and believe me it isn’t for the goodies you find in the caches, as most is little more than junk) are the places it takes you to. Geocaching showed me some interesting sites as I travelled along, what is really quite a large and remote part of the country. It really helped to break up some of those vast distances I was travelling.
ABOVE: Arriving in South Australia BELOW: Old Water Tower
ABOVE: Poor ‘Old Ted’ BELOW: Olary Railway Station
Other than the geocaching locations, one of the first stops of the day was at Cockburn, which marked the New South Wales – South Australian border. It was quite cold there, as it was for most of the journey across the southern stretch of Australia that I travelled on my holiday. But it was Olary that really caught my attention – a lovely old ‘bush’ type of town, seemingly lost in time. I loved the place, not that I saw a sole during the whole time I wandered about there – but to be fair it was cold and early.
ABOVE & BELOW: Morris Commercial at Olary
There were two main stops for fuel throughout the day. One at Yunta and one at Port Augusta – and these really were just quick pit stops to refuel. I then quickly moved on to Pimba and Woomera, staying the night in another cabin as I was still quite sick with the flu. This time I stayed at Woomera Traveller’s Village.
On this third day I travelled 600 km – giving me a total of 1769 km for the whole trip so far.
ABOVE: Concret Dice Near Yunta
Once again it was the usual ‘house keeping’ before bed – updating the daily journal, reviewing the holiday budget, checking in on social media, and editing and uploading photos. Then it was off to bed for an early start the next morning.
In an entertaining and somewhat chaotic episode of ABC’s Q&A (Monday 15th August) pitting science superstar Brian Cox against climate contrarian and global conspiracy theorist and now senator Malcolm Roberts, the question of cause and effect and empirical data was raised repeatedly in regard to climate change.
Watching I pondered the question – what would I need to change my mind? After all, I should dearly love to be convinced that climate was not changing, or if it were, it were not due to human emissions of CO2 and other greenhouse gases. That would make things just so much easier, all round.
So what would make me change my mind?
There are two elements to this question. The first is the observational basis, and the question of empirical data, of a changing climate. The second relates to cause and effect, and the question of the greenhouse effect.
On the second, I will only add that the history of our planet is not easily reconciled without recourse to a strong greenhouse effect. If you have any doubt then you simply need to read my former colleague Ian Plimer.
As I have pointed out before, in his 2001 award-winning book “A Short History of Planet Earth”, Ian has numerous references to the greenhouse effect especially in relation to what all young geologists learn as the faint young sun paradox:
“The early sun had a luminosity of some 30 per cent less than now and, over time, luminosity has increased in a steady state.”
“The low luminosity of the early sun was such that the Earth’s average surface temperature would have been below 0C from 4500 to 2000 million years ago. But there is evidence of running water and oceans as far back as 3800 million years ago.”
The question is, what kept the early Earth from freezing over?
Plimer goes on to explain: “This paradox is solved if the Earth had an enhanced greenhouse with an atmosphere of a lot of carbon dioxide and methane.”
With Ian Plimer often touted as one of the grand priests of climate contrarians, I doubt that Malcolm Roberts would consider him part of a cabal of global climate change conspiracists, though that would be ironic.
As a geologist, I need to be able to reconcile the geological record of a watery planet from time immemorial with the faint young sun hypothesis. And, as Ian points out, with nothing else on the menu, the greenhouse effect is all we have.
If the menu changes, then I will reconsider.
How about the empirical data?
Along with Brian Cox, I find it implausible that an organisation like NASA, with a record of putting a man on the moon, could or would fabricate data to the extent Malcolm Roberts insinuates. It sounds such palpable nonsense, it is something you might expect from an anti-vaxer.
However, a clear message from the Q&A episode is there is no way to convince Malcolm Roberts that the meteorological temperature data has not been manipulated to achieve a predetermined outcome. So he simply is not going to accept those data as being empirical.
the relevant data does not just include the records taken by meteorological authorities. It also includes the the record preserved beneath our feet in the temperature logs from many thousands of boreholes across all inhabited continents. And the importance of those logs is that they are reproducible. In fact Malcolm can go out an re-measure them himself, if he needs convincing they are “empirical”.
The idea that the subsurface is an effective palaeo-thermometer is a simple one that we use in our every day life, or used to at least prior to refrigeration, as it provides the logic for the cellar.
When we perturb the temperature at the surface of the earth, for example as the air temperature rises during the day, it sends a heat pulse downwards into the earth. The distance the pulse travels is related to its duration. As the day turns to night and the surface cools, a cooling pulse will follow, lagging behind, but eventually cancelling, the daily heating. The diurnal surface temperature perturbations produce a wave like train of heating and cooling that can be felt with diminishing amplitude down to a skin depth less than a metre beneath the surface before all information is cancelled out, and the extremes of both day and night are lost.
Surface temperatures also change on a seasonal basis from summer to winter and back again, and those temperatures propagate even further to depths of around 10 metres before completely cancelling .
On even longer cycles the temperature anomalies propagate much further,
and may reach down to a kilometre or more. For example, we know that over the last million years the temperature on the earth has cycled in and out of numerous ice ages, with a period of about 100,000 years. Cycles of that duration can propagate more than one kilometre into the earth, as we see in deep boreholes, such as the Blanche borehole near the giant Olympic Dam mine in South Australia. From our analysis of the Blanche temperature logs we infer a surface temperature amplitude of around 8°C over the glacial cycle.
So what do we see in the depth range of 20-100 metres that is sensitive to the last 100 years, and most relevant to the question of changing climate?
The image below shows the temperature log from a borehole that we purpose drilled in Gippsland as part of AuScope AGOS program.
The temperature profile shows various stages. Above the water table at about 15 metres depth, due to infiltration of groundwater in the vadose zone, the temperatures in the borehole rapidly equilibrate to seasonal surface temperature changes. In the winter, when this temperature log was obtained, the temperatures in this shallow zone trend towards the ambient temperature around 12°C. In summer, they rise to over 20°C. Beneath the vadose zone, the temperature in the borehole responds to the conduction of heat influenced by two dominant factors, the changing surface temperature on time-scales of decades to many hundred of years, and the heat flow from the deeper hot interior of the earth. During a rapid surface warming cycle lasting more than several decades the normal temperature gradient in which temperatures increase with depth can be reversed, so that we get a characteristic rollover (with a minimum here seen at about 30 metres depth).
In geophysics we use the techniques of inversion to identify causative signals, and their uncertainties, in records such as the Tynong borehole log, as well as in the estimation of the value of buried ore bodies and hydrocarbon resources. As shown in the second image, the inversion of the Tynong temperature log for surface temperature change over the last 700 years, with uncertainties at the 95% confidence interval, is compelling. Not surprisingly as we go back in time the uncertainties become larger. However, the inversion, which is based on Fourier’s law of heat conduction, shows that we can be confident that the Tynong AGOS borehole temperature record is responding to a long-term heating cycle of 0.3-1.3°C over the last century at the 95% confidence level.
If there were just one borehole that showed this record, it would not mean much. However the characteristic shallow rollover is present in all the boreholes we have explored, and has been reported in many thousands of boreholes from all around the world.
The only way we know to sensibly interpret such empirical evidence is that ground beneath our feet, down to a depth of around 50 metres or so is now heating from above. The physics that explains these observations dates back to Joseph Fourier, over 200 years ago, so its not exactly new or even contentious. In effect the solid earth below is now absorbing heat from the atmosphere above, counter to the normal process of losing heat to it. However, if Malcolm can bring to the table an alternative physics to explain these observations, while not falling foul of all the other empirical observations that Fourier’s law of heat conduction admits, then I am happy to consider, and put it to the test. (I suspect Brian Cox would be too, since all good physicists would relish the discovery of a new law of such importance as Fourier’s law).
Perhaps the hyper-skeptical Malcolm thinks that somehow the global cabal of climate scientists has got into all these thousands of boreholes with an electrical heater to propagate the heat signal that artificially simulates surface heating. More fool me.
But, if he does, then I am perfectly happy to arrange to drill a new borehole and, along with him, measure the temperature profile, making sure we don’t let those pesky climate scientists get at the hole with their heating coils before we have done so.
And I’ll bet him we can reproduce the signal from Tynong shown above.
But I’ll only do it on the condition that Malcolm agrees, that when we do (reproduce the signal), he will publicly acknowledge the empirical evidence of a warming world entirely consistent with NASA’s surface temperature record.
Malcolm, are you on? Will you take on my bet, and use the Earth’s crust as the arbiter? Perhaps Brian will stream live to the BBC?
Australia has some 8,300 islands, many of them home to threatened species. But humans have introduced rodents and predators such as feral cats and foxes to many of these islands, devastating native wildlife and changing entire island ecosystems. Removing invasive mammals has proven to be a very effective tool for protecting island species.
As a result, the federal government has made it a priority to remove invasive vertebrates from islands where they pose the most severe threats to native plants and animals.
But choosing where to remove those invasives is difficult. We don’t have complete information about the distribution of native species and threats across the nation’s 8,300 islands, and we haven’t been able to predict where eradication will have the most benefit.
However, in a recent study published in Nature Communications, our global team of scientists looked at islands around the world to consider where we can get the biggest bang for our buck.
It costs money to save species
The total cost of the recently completed rat and rabbit eradication on Macquarie Island was A$27 million. The proposed removal of rats from Lord Howe Island off New South Wales is expected to cost A$9 million.
Federal Environment Minister Josh Frydenberg has just announced funding to remove feral cats from five islands: Christmas Island, Dirk Hartog Island and the French Islands in Western Australia; and Bruny and King Islands in Tasmania.
Conservation dollars are limited, so it is important that these pricey interventions be focused on the islands where they will go the furthest toward conserving native island biodiversity.
Conversely, it is essential that we identify places where they won’t provide much benefit, either because a threatened species is likely to go extinct regardless of such interventions, or because the invasive species actually poses little threat.
We analysed the effects of invasive mammals on 1,200 globally threatened species across more than 1,000 islands to develop a model for where eradicating invasive wildlife will provide the greatest benefits to island species.
We estimate nearly half of threatened species populations on islands could disappear without conservation efforts. But targeted eradication could prevent 40-75% of these losses.
We found that just a few types of invasive mammals – rats, cats, pigs, mongooses and weasels – are most strongly associated with the disappearance of native species from islands.
Importantly, our study shows that the impacts of invasive mammals vary widely across the type of native species (native amphibians, birds, reptiles or mammals) and the conditions of the islands on which they live.
For example, we found that removing invasive mammals from small, dry islands could halve the extirpation risk for threatened native birds and mammals, but doing so on large, wet islands would have less benefit.
Australia’s most important islands
Our study included thirty-three Australian islands, home to 17 species of globally threatened birds, mammals and amphibians including the woylie (or brush-tailed bettong), Tasmania devils, black-browed albatross and Cooloola sedgefrog.
Eighteen of these islands are also home to introduced rats, cats or pigs, which potentially threaten native species with extinction.
Traditionally, we might assume that eradicating cats and rats would always reduce bird extinctions. However, our study suggests otherwise.
Rat or cat eradication may have little benefit on some islands. This is either because these invasive species have relatively minor impacts in some island environments, or because the native population is likely to go extinct regardless of conservation interventions.
So our study shows that of these 18 islands, eradicating invasive species on only two would likely prevent extinction of three native species populations. These are the eradication of cats and rats on Groote Eylandt in the Northern Territory, which would avert the extirpation (that is, the island-level extinction) of the northern quoll and northern hopping mouse; and the eradication of cats, rats and pigs on Flinders Island in Tasmania, which would avert the extirpation of the forty-spotted pardalote.
While this sounds like a tiny number, remember we haven’t looked at all of Australia’s islands and the species that live on them. Indeed, we only included species considered threatened at a global level. For the other islands not included in our study, species threatened with extinction at regional or national scales may – or may not – benefit from eradicating invasive species. As more information comes in on these islands, our analysis can suggest which of these we should focus on.