A couple of weeks ago we spent a few days on St Crispin's Reef. We went to that reef a couple of times last year, but this was demonstrably different.
The reef is part of the outer Great Barrier Reef, about 15 kilometres long and a six-hour sail from Port Douglas – about 50 kilometres off shore.
Anchoring is usually quite tricky. The large commercial tourist boats have their dedicated moorings, but in the 14.5-metre SV Biringari, we have to find our own anchoring spot in under 15 metres of water, which means reasonably close to the main reef and lots of beautiful but dangerous room or house-sized bommies, the tops of which can be less than a metre below the surface.
The trick is to anchor close enough to the reefs and bommies to make diving and snorkelling easy, but far enough away to allow for the yacht swinging around if the wind changes direction.
Going in, all except the skipper – usually one, two or three people – have to go on deck on "bommie watch". It is best to be there before 3pm, so the sun is high enough in the sky to reveal the bommies. The shallow water is turquoise, at least in the sun and in calm seas, whereas the surrounding sea is blue-grey.
But this time it was different. The bommies were strangely easier to see. They stood out even on this cloudy day with a bit of chop in the water. It was because since late last year a lot of the coral has been bleached, making the water above when viewed from a yacht look whiter.
As luck would have it, I had lent my underwater camera to someone who had returned it without the SIM card, but you do not need a camera to see bleaching.
It is not as if every coral on the whole reef had turned white, but many staghorn, plate and cabbage-leaf corals had done so.
About three-quarters of each of the half dozen bommies we looked at were unaffected. But that means a quarter was.
Bleaching occurs when the zooxanthellae (tiny algae) which live inside the coral polyps are expelled by the coral when water temperatures rise. And this summer they rose more than usual because of the combined effect of global warming and the El Nino effect.
The zooxanthellae produce pigments that can be seen through the clear bodies of the coral polyps. If they are expelled the coral loses its colour.
The coral can recover and get zooxanthellae back, but it is a race against time, because without the zooxanthellae, other algae can invade and cover the surface of the coral, killing the coral and leaving an ugly green-brown coating.
Scientists such as Professor Terry Hughes of James Cook University, who has done a large survey, say this summer's bleaching is the worst on record.
In a month or so we will know how much of the coral will recover. The coral polyps are animals, usually 1 millimetre to 3 millimetres in diameter. Given the millions of them that make up the reef, we will know whether humans have caused the extermination of perhaps the greatest number of animals in our history.
Bizarrely, there is an eerie beauty in much of the coral under bleaching stress. Before they are fully bleached you can see bright fluorescent blues and pinks in the coral – similar to the beauty of a dying star becoming a supernova. However beautiful, though, it is only temporary.
This mass extermination will not be of some pestilent insects, but of beautiful and very economically valuable animals.
The reef supports about 65,000 jobs in tourism, fishing, research and other activities and generates nearly $5 billion per year.
Sometimes economics is the only thing some people understand. An asset that generates $5 billion a year is worth at least $100 billion.
We should do everything we can to prevent its destruction – for its economic value and for its own sake.
But morally we cannot expect the rest of the world to reduce carbon emissions drastically to save our reef unless we are leading the effort ourselves. This is why the argument that Australia as a small part of the world economy can make little difference, therefore we should not bother, will not wash.
We should set ourselves the strictest targets so that we can be in a position to get world action. We should be seeking help from the US, Europe and Japan not to buy weapons systems with money we haven't got to attack enemies we don't have, but to deal with the real threat to our national well-being – climate change.
We should not be encouraging India to mine coal in Australia which will add to the threat. Rather we should encourage it to wean itself off coal and leave it in the ground.
This year's bleaching should serve as a warning to Australia and the world. After all, the Great Barrier Reef is the world's asset, too.
A lot of the reef may recover this time, but if there is another bleaching of this magnitude in the near future (very likely if we continue the way we are going) there could be so little left that the name Great Barrier Reef will be only a name.
Alas, it seems to be in human DNA to destroy the animals that sustain us.
The reef's tourism industry is desperate to underplay the bleaching, but it should be sounding alarm bells. It should be urging that, aside from climate change, governments can also act on other things that harm the reef over which we have direct control – such as chemical-laden run-off from agricultural land, coastal development and over-fishing.
As it happens, this month the ABC has been showing David Attenborough's documentary Great Barrier Reef. Attenborough has seen perhaps more of the natural world than anyone, so what he says about it really counts.
He said, "People say, what was the most magical moment in your career as a naturalist? And I always reply: 'The first time I put on a mask and went below the surface [on the Great Barrier Reef] and moved in three dimensions with just the flick of a fin, and suddenly saw all these amazing multi-coloured things living in communities right there.'
"You suddenly realise you can move in any direction. You're not harnessed by gravity any more. You're free. It's bliss. An extraordinary experience, like going into space – such splendour: all of these things moving through an architecture of coral. There's no equivalent anywhere else in the natural world."
His documentary was shot before the summer of 2015-2016. Let's hope we can make sure his words will still hold true in the future.