Human Impact On Earth's Sediment Cycle

One common type of argument I hear from anthropogenic climate change deniers is that human activity is too insignificant to affect the balance of global natural processes. On one debate a participant claimed that one large volcanic eruption emits more carbon dioxide than that by human activity. The actual amounts contradict this claim. Volcanism on earth emits about 0.13 -0.44 billion tons of CO2 per year. Human activity on the other hand emits about 35-40 billion tons of CO2 per year.

Jaia Syvitski and colleagues have produced a similar eye opening review of the human impact on earth's sediment cycle. The production, mobilization , transport, and deposition of sediment is based on a balance between tectonic processes, climate, erosion, and human activities. Our impact on sediment movement and its sequestration has now become so large that it dwarfs natural processes. 

The paper is open access for a limited time. Earth's sediment cycle during the Anthropocene. 

It is dense reading, full of numbers on sediment loads and fluxes.

"Human activities have increased fluvial sediment delivery by 215% while simultaneously decreasing the amount of fluvial sediment that reaches the ocean by 49%, and societal consumption of sediment over the same period has increased by more than 2,500%".

or: The Indus River once transported about 270 million tons of sediment to its delta. It presently deposits only about 13 million tons per year. So much of Indus water is siphoned off by canals, that it  often turns dry before reaching the sea.  

 and one more: "Large dams have trapped about 3,200 Gt of sediment since 1950 (ref.123), approximately 74% of which would likely have reached the coastal ocean". (Gt =billion tons)

There are many such stories from around the globe about the staggering amounts of sediment extracted and redirected for human use. Next time, don't shrug off the news you read about unregulated sand mining from our rivers. It is causing serious damage to riverine and coastal ecosystems.

The review ends with a proposal to set up a ‘Earth Sediment Cycle Grand Challenge’, a collaborative effort to better understand the changes to the sediment cycle. Such an initiative we surely need to address the many ongoing and future threats to our rivers and deltas.

Fire Initiated The Anthropocene

James C. Scott in his book Against The Grain: A Deep History of the Earliest States makes the case for the transformational impact of fire on our environment.

" Hominids' use of fire is historically deep and pervasive. Evidence for human fires is at least 400,000 years old, long before our species appeared on the scene. Thanks to hominids, much of the world's flora and fauna consist of fire adapted species (pyrophytes) that have been encourage by burning. The effects of anthropogenic fire are so massive that they might be judged, in an evenhanded account of the human impact on the natural world, to overwhelm crop and livestock domestication. Why human fire as landscape architect doesn't register as it ought to in our historical accounts is perhaps that its effects were spread over hundreds of millennia and were accomplished by "precivilized" peoples also known as "savages". In our age of dynamite and bulldozers, it was a very slow-motion sort of environmental landscaping. But is aggregate effects were momentous."

The impact of human activity on the earth's outer skin has been so considerable that atmospheric chemist Paul Crutzen proposed that we are now living in a new geologic epoch, which he called the Anthropocene. This has sparked a vigorous debate on whether a new division of our time scale is justified, and if it is, on where to place its beginning. James C. Scott make a distinction between what he terms the "thick" Anthropocene, contrasting with the idea of a  "thin" Anthropocene. 

A "thick" Anthropocene is manifest by a sudden appearance of a worldwide signal of human activity. Examples of this could be the advent of the Industrial Revolution, or even more catastrophically, the nuclear age in the 1940's which left global radioactive markers.  The "thick" Anthropocene appears to fit more closely geologic convention which demands that the beginning of a new geologic time unit need be recorded by a widespread and more or less synchronous preservation of biological and chemical changes. 

Scott calls fire, agriculture, and domestication as part of the complex that comprises a "thin" Anthropocene. These inventions changed the world patchily and slowly. Its signals appear here and there, not encoded in one geologic layer, but in many, smeared over the past few hundred thousand years. 

The term "more or less synchronous" I used to describe a new geologic boundary is relative to where in the geologic past the observer is. More recent changes are resolvable to a finer degree either as a matter of historical record or by methods like counting tree rings and annual/decadal growth layers in stalactites, cross calibrated by either carbon dating or some other radiometric dating method. The error bar increases as one goes further back in time. Take the great mass extinctions of the past. There will be a sediment layer to which a geologist can point to and state that this marks the boundary between say the Ordovician and the Silurian or the Permian and the Triassic. But that sediment layer certainly wasn't deposited instantaneously. It likely represents a few thousand years of elapsed time. If you were an observer who spent a few years in the Late Ordovician 443.8 million years ago, the situation would have been more akin to Scott's "thin" Anthropocene, with small changes occurring at different times in different places. You would have been unlikely to have anticipated the profound cumulative shift that would eventually accumulate.

Most mass extinctions which form the basis of the big divisions of geologic time unfolded over thousands of years, but their material record is collapsed into a few feet of sediment. We perceive these geologic turnovers as 'sudden' because the preceding and succeeding periods of relative stability lasted tens of  millions of years and the time the 'boundary layer' spans is unresolvable using our current dating methods.

The exception to this is that fateful day 66.03 million years ago, when a large meteorite struck what is now the Yucatan Peninsula. By the time the dust had settled (literally) in a few weeks, the world had irrevocably changed. The Cretaceous-Paleogene boundary layer is in an absolute time sense a truly instantaneous deposit. We interpret it as instantaneous, not by radiometric dating, but by using our understanding of the physical sedimentation processes that would have been triggered by the impact.

The lesson we can draw from the transformational events from deep geological time is not about the debates over the timing of Anthropocene but on its effect. Like those distant ecologic disruptions, we too have set off biological, chemical and physical processes on a different trajectory than they were several thousands of years ago. The Anthropocene will leave a permanent mark on the many future worlds to come.

Articles: Anthropocene, Future Of Science, India's Green Tribunal

Some excellent articles I read recently.

1) What Made Me Reconsider The Anthropocene - Peter Brannen. A lovely essay and one that is really a rethinking of his earlier position wherein he had dismissed the idea of Anthropocene as hubris.

I must share an excerpt:

"For me the essence of a lot of Faulkner is, before you can be something new and different, slavery is always there, the legacy of slavery is not erased, ‘The past is never dead. It’s not even past,’” he said. In Faulkner’s work, memories, the dead, and the inescapable circumstance of ancestry are all as present in the room as the characters who fail to overcome them. Geology similarly destroys this priority of the present moment, and as powerfully as any close reading of Absalom, Absalom! To touch an outcrop of limestone in a highway road cut is to touch a memory, the dead, one’s very heritage, frozen in rock hundreds of millions of years ago—yet still somehow here, present. And because it’s here, it couldn’t have been any other way. This is now our world, whether we like it or not.

The Anthropocene, for Wing, simply states that humans are now a permanent part of this immutable thread of Earth history. What we’ve already done means that there’s no unspoiled Eden to which we could ever return, even if we disappeared from the face of the Earth tomorrow.

2) Science Must Move With The Times: Phillip Ball. How has society shaped the nature of science over the past 150 years and what is the future course. A very thoughtful essay.

3) Woes of the National Green Tribunal: Are the recent appointments unconstitutional?:  The National Green Tribunal was set up to allow people access to environmental justice. Environmental lawyer Ritwick Dutta documents the way in which this institution is being undermined by the appointment of non-experts in the experts tribunal, by leaving zonal benches vacant, and by the subversion of video conferencing.

Read and weep!

"The situation with the zonal benches is even worse. Though touted as a great innovation, the video conference which is followed for hearing cases in Pune, Kolkata, Chennai and Bhopal does not allow the litigants or their lawyers to effectively make submissions. To make matters worse, speakers are frequently put on the ‘mute setting’ when the hearing is going on. Thus, it frequently happens that while advocates in zonal benches are making forceful arguments, they are not aware of the fact that they are not audible to the Judges sitting in Delhi, since the speaker is on mute setting".

Amazonia Before Columbus

This is an interesting article published in the Royal Society's Proceedings B.

During the twentieth century, Amazonia was widely regarded as relatively pristine nature, little impacted by human history. This view remains popular despite mounting evidence of substantial human influence over millennial scales across the region. Here, we review the evidence of an anthropogenic Amazonia in response to claims of sparse populations across broad portions of the region. Amazonia was a major centre of crop domestication, with at least 83 native species containing populations domesticated to some degree. Plant domestication occurs in domesticated landscapes, including highly modified Amazonian dark earths (ADEs) associated with large settled populations and that may cover greater than 0.1% of the region. Populations and food production expanded rapidly within land management systems in the mid-Holocene, and complex societies expanded in resource-rich areas creating domesticated landscapes with profound impacts on local and regional ecology. ADE food production projections support estimates of at least eight million people in 1492. By this time, highly diverse regional systems had developed across Amazonia where subsistence resources were created with plant and landscape domestication, including earthworks. This review argues that the Amazonian anthrome was no less socio-culturally diverse or populous than other tropical forested areas of the world prior to European conquest.

I had read 1491 by Charles Mann so none of this came  as a surprise  to me. I would recommend Mann's book  too.  It is a very well researched richly detailed book on the human landscape of the America's (south and north) before the European conquest. The Amazon basin is covered too and the two things that stuck with me are the "anthrosols" or soils produced or rather enriched in organic matter and nutrients by humans activity like mulching and composting. The map below shows the distribution of these anthropogenic soils.

 Source: Clement C.  et.al. 2015

Their concentrations along the banks of rivers match early European descriptions of farming communities settled along river bluffs, with the interfluvial areas being occupied by semi-nomadic and nomadic hunter gatherers.

The other aspect that fascinated me was the observation of Europeans of the incredibly varied fruit trees from the Amazon jungles. Many true wild fruit are generally small, sour, bitter, thorny, spiky. The native people over millennia had transformed them by selective breeding into the edible fruit smorgasbord that one sees today. Imagine large areas of "virgin" Amazon forests were actually abandoned fruit orchards!

Read this article though.