Wednesday, 27 September 2017

Cow farts and climate fiddling: has agriculture prevented a new glaciation?

Call me an old grouch, but I have to say that one of my bugbears is the use of the term 'ice age' when what is usually meant is a glacial period. We currently live in an interglacial (i.e. warmer) era, the last glaciation having ended about 11,700 years ago. These periods are part of the Quaternary glaciation that has existed for almost 2.6 million years and deserving of the name 'Ice Age', with alternating but irregular cycles of warm and cold. There, that wasn't too difficult now, was it?

What is rather more interesting is that certain geology textbooks published from the 1940s to 1970s hypothesised that the Earth is overdue for the next glaciation. Since the evidence suggests the last glacial era ended in a matter of decades, the proposed future growth of the ice sheets could be equally rapid. Subsequent research has shown this notion to be flawed, with reliance on extremely limited data leading to over-confident conclusions. In fact, current estimates put interglacial periods as lasting anywhere from ten thousand to fifty thousand years, so even without human intervention in global climate, there would presumably be little to panic about just yet.

Over the past three decades or so this cooling hypothesis has given way to the opposing notion of a rapid increase in global temperatures. You only have to read such recent news items as the breakaway of a six thousand square kilometre piece of the Antarctic ice shelf to realise something is going on, regardless of whether you believe it is manmade, natural or a combination of both. But there is a minority of scientists who claim there is evidence for global warming - and an associated postponement of the next glaciation - having begun thousands of years prior to the Industrial Revolution. This then generates two key questions:

  1. Has there been a genuine steady increase in global temperature or is the data flawed?
  2. Assuming the increase to be accurate, is it due to natural changes (e.g. orbital variations or fluctuations in solar output) or is it anthropogenic, that is caused by human activity?

As anyone with even a vague interest in or knowledge of climate understands, the study of temperature variation over long timescales is fraught with issues, with computer modelling often seen as the only way to fill in the gaps. Therefore, like weather forecasting, it is far from being an exact science (insert as many smileys here as deemed appropriate). Although there are climate-recording techniques involving dendrochronology (tree rings) and coral growth that cover the past few thousand years, and ice cores that go back hundreds of thousands, there are still gaps and assumptions that mean the reconstructions involve variable margins of error. One cross-discipline assumption is that species found in the fossil record thrived in environments - and crucially at temperatures - similar to their descendants today. All in all this indicates that none of the numerous charts and diagrams displaying global temperatures over the past twelve thousand years are completely accurate, being more along the lines of a reconstruction via extrapolation.

Having looked at some of these charts I have to say that to my untrained eye there is extremely limited correlation for the majority of the post-glacial epoch. There have been several short-term fluctuations in both directions in the past two thousand years alone, from the so-called Mediaeval Warm Period to the Little Ice Age of the Thirteenth to Nineteenth centuries. One issue of great importance is just how wide a region did these two anomalous periods cover outside of Europe and western Asia? Assuming however that the gradual warming hypothesis is correct, what are the pertinent details?

Developed in the 1920s, the Milankovitch cycles provide a reasonable fit for the evidence of regular, long-term variations in the global climate. The theory states that changes in the Earth's orbit and axial tilt are the primary causes of these variations, although the timelines do not provide indisputable correlation. This margin of error has helped to lead other researchers towards an anthropogenic cause for a gradual increase in planet-wide warming since the last glaciation.

The first I heard of this was via Professor Iain Stewart's 2010 BBC series How Earth Made Us, in which he summarised the ideas of American palaeoclimatologist Professor William Ruddiman, author of Plows, Plagues and Petroleum: How Humans Took Control of Climate. Although many authors, Jared Diamond amongst them, have noted the effects of regional climate on local agriculture and indeed the society engaged in farming, Professor Ruddiman is a key exponent of the reverse: that pre-industrial global warming has resulted from human activities. Specifically, he argues that the development of agriculture has led to increases in atmospheric methane and carbon dioxide, creating an artificial greenhouse effect long before burning fossil fuels became ubiquitous. It is this form of climate change that has been cited as postponing the next glaciation, assuming that the current interglacial is at the shorter end of such timescales. Ruddiman's research defines two major causes for an increase in these greenhouse gases:

  1. Increased carbon dioxide emissions from burning vegetation, especially trees, as a form of land clearance, i.e. slash and burn agriculture.
  2. Increased methane from certain crops, especially rice, and from ruminant species, mostly cattle and sheep/goat.

There are of course issues surrounding many of the details, even down to accurately pinpointing the start dates of human agriculture around the world. The earliest evidence of farming in the Near East is usually dated to a few millennia after the end of the last glaciation, with animal husbandry preceding the cultivation of crops. One key issue concerns the lack of sophistication in estimating the area of cultivated land and ruminant population size until comparatively recent times, especially outside of Western Europe. Therefore generally unsatisfactory data concerning global climate is accompanied by even less knowledge concerning the scale of agriculture across the planet for most of its existence.

The archaeological evidence in New Zealand proves without a doubt that the ancestors of today's Maori, who probably first settled the islands in the Thirteenth Century, undertook enormous land clearance schemes. Therefore even cultures remote from the primary agricultural civilisations have used similar techniques on a wide scale. The magnitude of these works challenges the assumption that until chemical fertilisers and pesticides were developed in the Twentieth Century, the area of land required per person had altered little since the first farmers. In a 2013 report Professor Ruddiman claims that the level of agriculture practiced by New Zealand Maori is just one example of wider-scale agricultural land use in pre-industrial societies.

As for the role played by domesticated livestock, Ruddiman goes on to argue that ice core data shows an anomalous increase in atmospheric methane from circa 3000BCE onwards. He hypothesises that a rising human population led to a corresponding increase in the scale of agriculture, with rice paddies and ruminants the prime suspects. As mentioned above, the number of animals and size of cultivated areas remain largely conjectural for much of the period in question.  Estimates suggest that contemporary livestock are responsible for 37% of anthropogenic methane and 9% of anthropogenic carbon dioxide whilst cultivated rice may be generating up to 20% of anthropogenic methane. Extrapolating back in time allows the hypothesis to gain credence, despite lack of access to exact data.

In addition, researchers both in support and opposition to pre-industrial anthropogenic global warming admit that the complexity of feedback loops, particularly with respect to the role of temperature variation in the oceans, further complicates matters. Indeed, such intricacy, including the potential latency between cause and effect, means that proponents of Professor Ruddiman's ideas could be using selective data for support whilst suppressing its antithesis. Needless to say, cherry-picking results is hardly model science.

There are certainly some intriguing aspects to this idea of pre-industrial anthropogenic climate change, but personally I think the jury is still out (as I believe it is for the majority of professionals in this area).  There just isn't the level of data to guarantee its validity and what data is available doesn't provide enough correlation to rule out other causes. I still think such research is useful, since it could well prove essential in the fight to mitigate industrial-era global warming. The more we know about longer term variations in climate change, the better the chance we have of understanding the causes - and potentially the solutions - to our current predicament. And who knows, the research might even persuade a few of the naysayers to move in the right direction. That can't be bad!

Monday, 11 September 2017

Valuing the velvet worm: noticing the most inconspicuous of species

Most of the recent television documentaries or books I've encountered that discuss extra-terrestrial life include some description of the weirder species we share our own planet with. Lumped together under the term 'extremophiles' these organisms appear to thrive in environments hostile to most other life forms, from the coolant ponds of nuclear reactors to the boiling volcanic vents of the deep ocean floor.

Although this has rightly gained attention for these often wonderfully-named species (from snottites to tardigrades) there are numerous other lifeforms scarcely noticed by anyone other than a few specialists, quietly going about their unassuming business. However, they may provide a few useful lessons for all of us, including that we should acknowledge there may be unrecognised problems generated when we make rapid yet radical modifications to local environments.

There is a small, unassuming type of creature alive today that differs little from a marine animal present in the Middle Cambrian period around five hundred million years ago. I first read about onychophorans in Stephen Jay Gould's 1989 exposition on the Burgess Shale, Wonderful Life, and although those fossil marine lobopodians are not definitively onychophorans they are presumed to be ancestral. More commonly known by one genus, peripatus, or even more colloquially as velvet worms, there are at least several hundred species around today, possibly many more. The velvet component of their name is due to their texture, but they bear more resemblance to caterpillars than to worms. They are often described as the ‘missing link' between arthropods and worms but as is usually the case this is a wildly inappropriate term in this context of biological classification. The key difference to the Burgess Shale specimens is that today's velvet worms are fully terrestrial: there are no known marine or freshwater species.

Primarily resident in the southern hemisphere, the largely nocturnal peripatus shun bright light and requiring humid conditions to survive. Although there are about thirty species here in New Zealand, a combination of their small size (under 60mm long) and loss of habitat means they are rarely seen. The introduction of predators such as hedgehogs - who of course never meet peripatus in their northern hemisphere home territory - means that New Zealand's species have even more to contend with. Although I frequently (very carefully) look under leaf litter and inside damp logs on bush walks in regions known to contain the genus Peripatoides - and indeed where others have told me they have seen them - I have yet to encounter a single specimen.

There appears to be quite limited research, with less than a third of New Zealand species fully described. However, enough is known about two species to identify their population status as 'vulnerable'. One forest in the South Island has been labelled an 'Area of Significant Conservation Value' thanks to its population of peripatus, with the Department of Conservation relocating specimens prior to road development. Clearly, they had better luck locating velvet worms than I have had! It isn't just the New Zealand that lacks knowledge of home-grown onychophorans either: in the past two decades Australian researchers have increased the number of their known species from just seven to about sixty.

Their uncanny resemblance to the Burgess Shale specimens, despite their transition from marine to terrestrial environments, has led velvet worms to be described by another well-worn phrase, 'living fossils'. However, is this short-hand in any way useful, or is it a lazy and largely inaccurate term? The recent growth in sophisticated DNA analysis suggests that even when outward anatomy may be change little, the genome itself may vary widely. Obviously DNA doesn't preserve in fossils and so any such changes cannot be tracked from the Cambrian specimens, but the genetic variation found in other types of organisms sharing a similar appearance shows that reliance on just external anatomy can be deceptive.

Due to lack of funding, basic taxonomic research, the bedrock for cladistics, is sadly lacking. In the case of New Zealand, some of the shortfall has been made up for by dedicated amateurs, but there are few new taxonomists learning the skills to continue this work - which is often seen as dull and plodding compared to the excitement of, for example, genetics. Most people might say so what interest could there be in such tiny, insignificant creatures as peripatus? After all, how likely would you be to move an ant's nest in your garden before undertaking some re-landscaping? But as shown by the changing terminology from 'food chains' to 'food webs', in most cases we still don't understand how the removal of one species might generate a domino effect on a local ecosystem.

I've previously discussed the over-reliance on 'poster' species such as giant pandas for environmental campaigns, but mere aesthetics don't equate to importance, either for us or ecology as a whole. It is becoming increasingly clear that by weight the majority of our planet's biomass is microbial. Then come the insects, with the beetles prominent both by number of species and individuals. Us large mammals are really just the icing on the cake and certainly when it comes to Homo sapiens, the rest of the biosphere would probably be far better off without us, domesticated species aside.

It would be nice to value organisms for themselves, but unfortunately our market economies require the smell of profit before they will lift a finger. Therefore if their usefulness could be ascertained, it might help generate greater financial incentive to support the wider environment. Onychophorans may seem dull, but there are several aspects to them that is both interesting in itself and might also provide something fruitful for us humans.

Firstly, they have an unusual weapon in the form of a mechanism that shoots adhesive slime at prey. Like spider silk, is it possible that this might prove an interesting line of research in the materials or pharmaceutical industries? After all, it was the prickly burrs of certain plants that inspired the development of Velcro, whilst current studies of tardigrades (the tiny 'water bears' living amongst the mosses) are investigating their near indestructability. If even a single, tiny species becomes extinct, that genome is generally lost forever: who knows what insights it might have led to? Although museum collections can be useful, DNA does decay and contamination leads to immense complexities in unravelling the original organism's genome. All in all, it's much better to have a living population to work on than rely on what can be pieced together post-extinction.

In addition, for such tiny creatures, velvet worms have developed complex social structures; is it possible that analysis of their brains might be useful in computing or artificial intelligence? Of course it is unlikely - and extinction is nothing if not natural - but the current rate is far greater than it has been outside of mass extinctions. Losing a large and obvious species such as the Yangtze River dolphin (and that was despite it being labelled a ‘national treasure') is one thing, but how many small, barely-known plants and animals are going the same way without anyone noticing? Could it be that right now some minute, unassuming critter is dying out and that we will only find out too late that it was a vital predator of crop-eating pests like snails or disease vectors such as cockroaches?

It has been said that ignorance is bliss, but with so many humans needing to be fed, watered and treated for illness, now more than ever we need as much help as we can get. Having access to the complex ready-made biochemistry of a unique genome is surely easier than attempting to synthesise one from scratch or recover it from a long-dead preserved specimen? By paying minimal attention to the smallest organisms that lie all around us, we could be losing so much more than just an unobtrusive plant, animal or fungus.

We can't save every species on the current endangered list but more attention could be given to the myriad of life forms that get side-lined by the cute and cuddly flagship species, usually large animals. Most of us would be upset by the disappearance of the eighteen hundred or so giant pandas still left in the wild, but somehow I doubt their loss would have as great an impact on the surrounding ecosystem than that of some far less well known flora or fauna. If you think that's nonsense, then consider the vital roles that bees and dung beetles play in helping human agriculture.

Although the decimation of native New Zealand wildlife has led to protective legislation for all our vertebrates and a few famous invertebrates such as giant weta, the vast majority of other species are still left to their own devices. That's not to say that the ecosystems in most other countries are given far less support, of course. But without funding for basic description and taxonomy, who knows what is even out there, never mind whether it might be important to humanity? Could it be that here is a new field for citizen scientists to move into?

Needless to say, the drier climes brought on by rising temperatures will not do peripatus any favours, thanks to its need to remain in damp conditions. Whether by widespread use of the poison 1080 (in the bid to create a pest-free New Zealand by 2050) or the accidental importation of a non-native fungus such as those decimating amphibians worldwide and causing kauri dieback in New Zealand, there are plenty of ways that humans could unwittingly wipe out velvet worms, etal. So next time you watch a documentary on the demise of large, familiar mammals, why not spare a thought for all those wee critters hiding in the bush, going about their business and trying to avoid all the pitfalls us humans have unthinkingly laid for them?