Matthew's Journal

Earlier this week, I went to a seminar given by Charles Sheppard, on the impact of climate change on marine ecosystems. It was quite interesting, and thoroughly depressing. He opened with "It's very easy to get depressed looking at the evidence of the damage climate change is causing. Instead, as a scientist, I like to see it as exciting - we're taking part in the biggest experiment ever!", and it went from there...

One of the more obvious signs of climate change is the death of coral reefs. Here it's not the mean temperature rise that kills them, but the peak temperatures. Especially in shallower waters like the Persian Gulf, there have been several extreme temperature events, which have resulted in "bleaching" - the living parts of the corals die. It takes around 5 years for many corals to grow to maturity and be able to reproduce, so as these extremes of temperature become more frequent, they'll never be able to reproduce, and will go extinct at least locally. This is predicted to become common by about 2020. Furthermore, the marine parks where we try and keep pollution and over-fishing at bay were not rationally selected, so they often don't correspond to the more thermally resistant corals - i.e. they're essentially a waste of time.

Another problem for marine ecosystems is the acidification of the oceans. For reasons I don't quite recall (or failed to understand at the time!), this is a time-delayed process - if we never turned on another engine after today, the oceans would continue to acidify for another 40 years or so. Now, there's a lot of limestone at the bottom of the ocean which buffers the system, so it's not going to get especially acidic in chemical terms, but the biological impact will be significant. Already, little plankton are having their shells etched by the acidity of sea-water, and by 2050 it will be impossible to calcify things in the sea. That has significant impacts on all sorts of things, although whether we'll be stuck with "jelly-fish and chips" is anyone's guess. Particularly, it means that corals will be unable to grow at all, which means many people will starve. Already a few million extra deaths are year are due to malnutrition attributable to climate change (either directly, or due to increased susceptibility to disease).

Many of these changes are going to happen, unless we find a way to sequester vast amounts of Carbon out of the atmosphere, and fast.

As an aside, there is controversy regarding the role of air travel in climate change. After 11/09/2001, air travel was grounded in the USA for 3 days; this resulted in a raising of air temperatures across America, as reported in Nature (PDF). Charles' view was that this might well be significant - that the cooling effect of jet contrails (which are largely water vapour) might outweigh the CO2 produced by jets. He also claimed that CO2 output by air travel was tiny compared to other sources (especially shipping, and private car use), so we should stop worrying about flying places, and instead look at the bigger CO2 sources.

All a bit disheartening, really.

Influenza has been making the news recently - bird 'flu is spreading Westwards from Asia, and comparisons are being made to the 1918 Spanish 'flu epidemic that killed around 50 million people.

The 1918 influenza outbreak has popped up during my research a few times, most notably in the work of Sattenspiel and colleagues into its dynamics in the Canadian subarctic (The Hudson Bay Trading Company kept detailed accounts of the movement of people and influenza, which has provided the raw material for a small network study). There has for some time been speculation about the nature of the virus which caused the 1918 pandemic, and it has recently been sequenced in its totality[1]. It has subsequently been created in a laboratory, and demonstrated to be highly lethal in mice[2]. There has been some debate as to whether publishing the full sequence and then actually building a very similar virus was sound or not, but the scientific consensus seems to be that it was; I agree with that, so I won't say anything more on it for now.

What is significant about this work is that it suggests a hypothesis about the origin of the 1918 strain, as distinct from the pandemic strains from 1957 and 1968 (which were substantially less serious). The 1918 strain killed far more people than these other pandemic strains, and was proportionally far more dangerous to otherwise healthy 20-40 year-olds. Specifically, it appears to have arisen by direct evolution of an highly pathogenic avian influenza strain, rather than by assortment of genes between avian and human strains infecting the same host (as is thought to be the case for the 1957 and 1968 strains).

What of the current H5N1 bird 'flu, then? In the human cases, viruses isolated have had some of the same changes that the 1918 strain did, suggesting that this virus may be making similar evolutionary changes to those the 1918 strain did to enable it to become highly infectious between humans; current cases are largely thought to have been the result of birds (or bird waste) infecting humans. The concern that the current H5N1 strain may make the evolutionary step to being readily transmissible between humans is understandable, therefore.

Unfortunately, it is impossible to say if, never mind when, this change might occur, nor indeed how dangerous the resulting virus would be. Global travel patterns would certainly contribute to its rapid dissemination across the world, but it may yet become less pathogenic to humans whilst evolving to become more transmissible between them. The WHO is encouraging governments to prepare for the worst, and rightly so, but only time will tell how bad it will be (if it happens at all)...

[1] Taubenberger et al, Nature 437, 889-893 (2005)
[2] Tumpey et al, Science 310, 77-80 (2005)