In Defence of Humanity
A paper “Defining the Anthropocene” by Lewis and Maslin of the University of Leeds in the UK appeared in Nature last week. The abstract reads:
Time is divided by geologists according to marked shifts in Earth’s state. Recent global environmental changes suggest that Earth may have entered a new human-dominated geological epoch, the Anthropocene. Here we review the historical genesis of the idea and assess anthropogenic signatures in the geological record against the formal requirements for the recognition of a new epoch. The evidence suggests that of the various proposed dates two do appear to conform to the criteria to mark the beginning of the Anthropocene: 1610 and 1964. The formal establishment of an Anthropocene Epoch would mark a fundamental change in the relationship between humans and the Earth system.
It is not a new idea. There have various permutations of the name: Anthropozoic (Stoppani 1873), Anthrocene (Revkin, 1992), Homogenocene (Samways, 1999) culminating in Anthropocene (Crutzen and Stoermer, 2000) and there have been various permutations of the idea itself, e.g. Ruddiman (2003): The anthropogenic greenhouse era began thousands of years ago.
Then what is the significance of 1610 and 1964? Why all the fuss?
1964 was the era of atomic testing which left its mark on the trace concentration of various gaseous isotopes in the atmosphere. Lewis and Maslin rightly dismiss this as a marker because it has had no discernible effect for those of us who do not have access to a mass spectrometer. For them the important thing is the dip in atmospheric CO2 concentrations which occurred in 1610 which they have pompously dubbed the Orbis Spike.
Scientific American’s take on it is as follows:
Much like the golden spike that marks the end of the dinosaurs, the proposed Orbis spike itself would be tied to the low point of atmospheric CO2 concentrations around 1610, as recorded in ice cores, where tiny trapped bubbles betray past atmospheres…
The CO2 drop coincides with what climatologists call the little ice age. That cooling event may have been tied to regenerated forests and other plants growing on some 50 million hectares of land abandoned by humans after the mass death brought on by disease and warfare, Lewis and Maslin suggest. And it wasn’t just the death of millions of Americans, as many as three quarters of the entire population of two continents. The enslavement (or death) of as many as 28 million Africans for labor in the new lands also may have added to the climate impact. The population of the regions of northwestern Africa most affected by the slave trade did not begin to recover until the end of the 19th century. In other words, from 1600 to 1900 or so swathes of that region may have been regrowing forest, enough to draw down CO2, just like the regrowth of the Amazon and the great North American woods, although this hypothesis remains in some dispute.
Clearly humanity has had, and continues to have, a marked effect on large chunks of the planet. Farmland has replaced forest over most of North-western Europe, for example, and this process has been happening for millennia. What is new is the idea that there is a significant spike in atmospheric CO2 which is of major importance. Close examination of the CO2 record shows that there was indeed a slight dip which minimized around 1610 but there is no evidence to link this blip to the Little Ice Age nor to the putative disruption of American farming communities. It precedes the Maunder Minimum in solar activity by a couple of decades and so is unlikely to have a solar origin. It is most likely random noise.
It seems the purpose of the paper is give a scientific-sounding name to the effect humanity is having on the planet, the subtext being that such effect must be an unmitigated Bad Thing. Googling “anthropocene ruin” generates 248,000 hits: The year humans started to ruin the world (Bloomberg, Sydney Morning Herald), The year humans caused irreversible damage to the earth (Daily Mail) and on and on.
A common lament is the supposedly increased rate of species extinction, always assumed, of course, to be the result of human carelessness. Species extinction rates vary widely over time. The last great extinction occurred during the Paleocene and Eocene epochs between 65 and 37 million years ago. At the end of the Paleocene, a major episode of faunal turnover (extinction and origination) largely replaced many archaic groups with essentially modern groups which include primitive horses, rhinoceroses, tapirs camels and deer, rodents, rabbits, bats, proboscideans, and primates. In the late Eocene an episode of global cooling triggered changes in the vegetation that converted areas of thick rainforest to more open forest and grasslands, thereby causing another interval of evolutionary turnover that included the disappearance of the last of the primitive herbivores.
We should remember that humans have added hugely to biodiversity during the present epoch, the Holocene. Many varieties of domesticated animals and plants have been brought into existence by selective breeding by humans; think of all the multitudinous varieties of maze, of potatoes, of roses, of horses and cattle and dogs. Think of dogs. The dog, as we know it, would not exist but for us; there would only be wolves, coyotes and jackals. There may well be a case for renaming the entire Holocene, the Anthropocene. The idea that a geological epoch should start at a fixed calendar date is ridiculous.
It might be might be argued that varieties are not the same thing as species and that in that sense we have not increased biodiversity. That may be so but in effect all new species start out as varieties. The subtle genetic changes, which prevent different species interbreeding, happen quietly in the background. It is not obvious when a new species comes into existence whereas it is noticeable when a species becomes extinct. There is more than a whiff of Creationism in people such as David Attenborough striving so energetically to keep declining species in existence. Evolution hasn’t stopped; Planet Earth is a work in progress.
Lewis and Maslin’s paper isn’t science: it is Green propaganda.