Category: Climate Change

We are about to lose all our shallow water tropical reefs. From Australia’s Great Barrier to the shifting shoals of the Bahamas, the world’s warm-water ecosystems are facing total destruction—possibly within ten to twenty years. The only way to avoid this catastrophe is to keep global temperature rise below 1.5 centigrade.

There are many reasons why climate scientists are coming to the view that even a 2 °C rise is too much. From increasing incidence of extreme weather events—such as the still unfolding disaster in southern Africa—to the likely impact on world crops and the complete disappearance of island nations, there is much that could be said on this topic. And the change, from believing that 2 degrees is “safe” to now looking for no more than a 1.5 centigrade increase, is the main reason why we are suddenly seeing headlines such as “only 12 years to save the planet”.

In a short column I can’t properly discuss all the potential problems. So, I’m going to concentrate on coral reef destruction. There are several reasons for this. For a start, it’s a subject I can claim expertise in as, 30 years ago, I was one of the first people to build computer models of how coral reefs grow. Furthermore, large-scale extinctions are going to be the longest lasting effect of global-warming. The fossil record shows us that, following big losses of biodiversity, it take 5-10 million years for Earth to recover. The final reason for looking at tropical reefs is that they are a “climate canary”. Canaries were taken down mines to give early-warning of dangerous gas build-up and, if increasing loss of our reefs does not provide a wake-up call to the world that greenhouse gas build-up is serious, I suspect nothing will.

Total destruction of all tropical coral reefs sounds like an exaggeration but there are good reasons for making such a dramatic statement. The issue is coral-bleaching—the fact that excessively warm water turns corals white. This happens because corals are not one organism but two. The coral polyp itself is an animal but it hosts a plant in what’s called a symbiotic relationship—a partnership that provides benefits to both participants. In this case, the plant feeds the coral and the coral shelters the plant. Bleaching happens if water becomes a few degrees too warm, for more than a few weeks, since the warmth kills the symbiotic plant and the coral then loses its colour and eventually dies.

Bleaching is a natural process that happens now and again and has done so for millions of years. Normally it’s not a problem because new corals grow back after about ten years and the frequency with which coral reefs find themselves in hot water is much less than once a decade. The problem is that global warming is increasing this frequency. Today, with one degree of warming, bleaching occurs about once a decade and our reefs are struggling. By fifteen years’ time or so—when warming will probably get to 1.5 degrees if we don’t do anything—the frequency will have risen to about once every two and half years and most reefs will be dying. If we get to a two centigrade rise, reefs will bleach every year and they are doomed.

First published in Marlborough.news

Don’t take my word—or anyone else’s—for anything. You don’t need to. The data is so clear that you can see, for yourself, the reality of human-induced climate change.

The graph above has two curves. The first, in blue, shows the cumulative amount of carbon dioxide that we’ve put into the atmosphere since 1880 whilst, in red, you can see how temperatures have risen since that same year. Temperatures fluctuate a bit, as you’d expect, but the two curves are remarkably similar. They rise together, in lockstep, and certainly seem to be strongly linked. However, this doesn’t necessarily mean that human carbon dioxide emissions are causing temperature change. There are four other ways the similarity could be explained:

Perhaps climate science has got things back to front so that, in reality, temperature rises are causing increased emissions. I hope you can see how ridiculous that is! It implies that the rapid improvements in standards of living (and hence emissions) since the industrial revolution were driven by warming rather than by human innovation. Another possibility is that emissions and temperature are both pushed by some third factor. Personally, I can’t think of anything that could do that. Can you?

A third alternative is that it’s just a coincidence. Perhaps the two curves will start to look different if we just wait a little longer. Well, this isn’t the place for a statistics lesson but it’s quite easy to work out that two curves will look this similar, by chance, less than 0.1% of the time. So it could be a coincidence but it’s not very likely. Would you bet the future of your grand-children on odds of a thousand to one against?

The final possibility is fraud. That would require conspiracy on an enormous scale as the data used in these graphs has been collected by thousands of different people over a period of 130 years. There would need to have been collusion, from the beginning, between collectors of economic data (mostly tax collectors) and collectors of temperature data (Victorian vicars, 20th century sea captains and NASA). Seems implausible to me.

So the only sensible conclusion is the scientifically conventional one—human greenhouse gas emissions are causing climate change.

The graphs also show that 1500 billion tonnes of carbon dioxide have elevated temperatures by about a degree. So, naively, we can only emit another 750 billion tonnes if we want to keep the temperature rise below 1.5 °C. This simple-minded calculation is backed up by the much more sophisticated calculations of the Intergovernmental Panel on Climate Change (IPCC) whose report last October estimated that we can emit another 770 billion tonnes.

That sounds a lot but, with seven and a half billion people on the planet, it’s only another 100 tonnes each. Unfortunately, a typical Brit produces about seven tonnes a year and so we’ll all use our remaining share within 15 years. We all need to go on a carbon diet and lose a few hundred kilograms a year each year. Two or three hundred kilograms a year is actually not that hard and I’ll talk about how in a future column. But, in my next one, I want to look at why we think a 1.5 °C rise is the maximum safe limit. It’s not a big temperature difference so why all the fuss?

First published in Marlborough News Online