Water Vulnerability

So we've looked at how the human population affects (and has in the past affected) green house gas concentrations and biodiversity (animals and plants). Now I want to take a quick look at our effect on water, so here's a brief summary of Vörösmarty et al.'s (2000) article where they look at how climate change and population growth affect water stress.

They point out that a lot of focus has been on how global warming contributes to water vulnerability whereas actually direct human impact (i.e. consumption) is a lot more important than we think. They emphasise that future water demand will be based on population growth, economic development and projected changes in water use efficiency and what they find, which I think is interesting, is that water use per capita is expected to decline. So although there will be increased water stress that won't be due to an intensification of use, it will be down to population growth, migration, and development. Couple this with the fact that most of the world's population growth will now take place in cities, and you get all the issues around pollution and water-borne diseases. 

What they also determine (which you can see in the maps below) is that not only is a large portion of the world under water stress (I don't think it's the first time we've heard that though), but rising water demands are more important than greenhouse warming in "defining the state of the global water system until 2025" (p.1). You can see below: (without getting into too much complication), the fact that there is more red colour in the middle diagram than in the first means that population change has more of an effect than simply climate change on water demand and use. Obviously when the two are combined they have the biggest effect. And as climate change gets more significant as time goes on, this effect on water stress will get worse and worse and (judging by what the authors said) I'm assuming climate change may even overtake population change as having the most significant effect (as either population growth is slowing, or the lag between human activities and climate change comes into effect).

Anyhow, it is clear that humans and the growth of the human population are having effects on water vulnerability – directly through use and demand; and indirectly through causing environmental change.

  

source: Vörösmarty et al. (2000)

Biodiversity & Extinction

I would like to focus on some of the impacts the growing human population has had on the environment other than greenhouse gas emissions, or nitrogen addition. This week I want to take a look at how humans have in the past, and are now more than ever, affecting the other living things on our planet. This is important not only because species loss is bad in itself but because biodiversity is crucial to the productivity and sustainability of the Earth's systems (see Hooper et al. 2012 for more info). I don't want to make this post too long and boring so I'm going to concentrate on the role humans played in the past megafaunal extinctions and the evidence for an imminent 6th mass extinction in the Anthropocene as a result of human population growth and resource demands.

We know that humans have played a part in extinctions in the past. Barnosky et al. (2004) examine the evidence for the respective roles of climate and humans in the Pleistocene megafaunal extinctions and find that although there is a strong case backing climate variability, the effects were coupled with, and amplified by human action such as hunting. For example, many of the surviving animals were nocturnal, lived in dense, hight forest or even in the sea, so if climate was the only culprit, why did these habitat-specific species survive?

The authors find while comparing the timelines of the late Quaternary extinctions, human arrivals and climate change, that human arrival coincided with many extinction events and played a very significant role in the extinctions that occurred on the American and Australian continents (see below). Humans don't take all the blame of course, and they conclude that:

"A significant implication for conservation biology is that the coupling of marked climatic change with direct human impacts on fauna is especially pernicious. Both effects are under way today at unprecedented rates."

So I see this as a warning of what humans are capable of, and at that time there weren't very many of us! Think about today, with 7 billion of us! In fact this is exactly the line of reasoning many take to lead to the idea that in the Anthropocene, we could be very well moving towards a 6th mass extinction.







Source: Barnosky et al. (2004)

So given all that we know about the massive growth in human poopulation and activity, and that human populations clearly have an effect on extinction rates - through co-opting resources; fragmenting habitats; introducing non-native species; spreading pathogens; hunting; and changing the global climate - could we be heading towards the Earth's sixth mass extinction? We seem to hear about endangered species every day on the news and there is a general perception that our activities are causing more extinctions than is 'normal' - but what is the evidence? A paper published in 2011 by Barnosky et al. concludes that we aren't currently in a mass extinction (as compared to the previous five) but warns that if no measures are taken to protect endangered species, we could well end up in one.

The study compares the rate and magnitude of current extinctions with those of the past five mass extinctions, using the metric 'extinction per million species years' (E/MSY). They take two approaches: firstly if we assume the 'Big 5' all happened suddenly - say, over 500 years - what extinction rate would have been needed and how does that compare to the present rate? They find that that current rates are slower, but if we were to consider 'threatened' species as inevitably extinct then the rates would be comparable. For the second approach, they ask how long it would take to produce species loss equivalent to 'Big 5' magnitudes at current extinction rates. In fact if all 'threatened' species became extinct within a century and the rate remained constant, such magnitudes would be reached in 240-540 years.

This seems like a long time, but who is to say that extinction rates won't increase? The human population is growing, but also becoming wealthier. The rapid development of many Asian countries, especially China, means that there are way more people demanding the kind of lifestyle that requires activities that are harmful to biodiversity. Of course, you could argue the other way, that there is a lot of uncertainty about what 'normal' rates are and whether the results for the particular taxa they studied (due to better fossil records) can be extrapolated to other species in other places. 
Nevertheless, the authors stress that fossil records show that species richness and evenness today are low compared to pre-Anthropogenic conditions, and I stress that one of the principal differences between present day and the pre-Anthropocene era is the size of the human population. Gaston (2005) writes that:

"The most important agent of change in the spatial patterns of much of biodiversity at present is ultimately the size, growth and resource demands of the human population. This is giving rise to [...] levels of species extinction largely unprecedented outside periods of mass extinction" 

Source: http://www.biologicaldiversity.org/campaigns/overpopulation/index.html

I obviously only touched on the issues of extinction and biodiversity as the main focus of this blog is overpopulation, but if you'd like the read more about them, here are some links to blogs on the topics:

http://at-the-edge-of-extinction.blogspot.co.uk/

http://holoextinction.blogspot.co.uk/

http://bdchanges.blogspot.co.uk/2013/10/invasive-species-not-all-that-bad.html

http://anthropocenebiodiversity.blogspot.co.uk/

http://thefinalcountdown-biodiversity.blogspot.co.uk/



From the Media

Here are a few links to news stories from the past week and a 'Kal's cartoon' from The Economist archives:

• China decides to relax its one-child policy in the future

• Hans Rosling appears on BBC2 and tells us not to panic about population explosion and that measured approaches are doing the trick

• French study parallels the UN by predicting world population will rise to 9.7 billion by 2050

Source: www.economist.com

The Early Anthropogenic Hypothesis

Before I continue any further, I feel I have to mention Ruddiman's 2003 paper in which he argues that the Anthropocene began much earlier than the Industrial Revolution: about 8000 years ago. I know it's not directly about population growth, but in my eyes his hypothesis shows what impact even a tiny, 'non-consumer' human population can have (and possibly did have) on the environment and its systems.

He compares the Holocene with previous interglacials and forms three main arguments:

1. That Earth-orbital-driven cyclic variations (phew!) in CO2 and CH4 (methane) during the past 350,000 years would predict a decline in those gas concentrations throughout the Holocene but they began anomalous increases, 8000 years ago for CO2 and 5000 years ago for CH4
2. Possible explanations for those rises based on natural forcing can be refuted by paleoclimatic evidence
3. Archaeological, cultural, historical and geological evidence leads to anthropogenic explanations linked to early agriculture in Eurasia (forest clearance 8000 years ago; rice irrigation 5000 years ago)

source: Ruddiman (2007)

He looks at CH4 concentrations in Vostok ice, which show that they followed the 23,000 year orbital insolation cycle. This supports the orbital-monsoon theory that higher CH4 concentrations had their root cause in orbital precession-dominated summer insolation changes which meant monsoons were more extreme and there was more flooding. However, 5000 years ago, the CH4 signal started to increase, departing from the continued decrease expected from orbital monsoon theory (see figure A above). This risks getting very dry and technical so I'm just going to say that by the industrial era the methane concentration 'should' have been 250 ppb lower than it actually was.

As for CO2 concentration, he compares with previous interglacials and finds that in the last 3, CO2 increase reached a maximum and then dropped steadily for around 10,000 years, whereas in the Holocene CO2 concentrations did peak and start to decline around 10,000 years ago, but then started to rise 8000 years ago (see figure B above). He goes on to prove his point through examining trends at each of the 3 major orbital cycles but I'm not going to go into all of that otherwise this will turn into an essay! If you fancy reading the article (which I recommend), just click on the link above.

He continues by refuting other possible explanations: that natural loss of terrestrial biomass or changes in ocean carbonate chemistry could explain the CO2 rises. They could explain part of the rise, but not nearly enough.

He then proposes his 'famous' idea: that pre-industrial land clearance and rice irrigation are responsible. He points to the domestication of horses and the invention of the ox-drawn plow 6000 years ago, and shows that the pollen sequences in central Europe younger than 6-5000 years are altered enough that pollen analysts view them as unrepresentative of 'natural vegetation'. There was also rapid sediment accumulation in central European lakes between 5000 and 3000 years ago – backing up the claim of forest clearance. Finally the brief periods of CO2 decline could be matched with periods of human pandemics like the bubonic plague. This also backs up the deforestation idea as killing off vast portions of the human population would have meant a halt (or at least significant slowing!) to human activities such as deforestation and as many 'infected' areas were abandoned – a regrowth of forests!

Ruddiman published a response article in 2007, where he addresses the (many) challenges his work has faced. However, he still finds the CO2 and CH4 gas trends anomalous, despite having reviewed the ice timescale used. He still finds that extreme biomass burning (forest clearing) and rice irrigation can explain the anomaly. However, only about 25% of the 'excess' CO2 could come from carbon from deforestation but he proposes that the climate system feedback is responsible e.g. the ocean remained warm because of anthropogenic intervention. Finally pandemics can explain only half the CO2 decreases, but they obviously still had some effect.

Although being precise about these claims is very difficult, there is no doubt that humans did have some effect on their environment, even when they did not possess the technology (or demand) for resource exploitation. It is clear then that humans today have an even greater impact on their environment, and there are many many more of them.

UCL Lunch Hour Lecture

Last month, UCL's Judith Stephenson gave a lunch hour lecture titled 'Global Growth vs Human Health: Finding the Balance'. She is from the Institute for Women's Health so not an environmentalist but the talk was interesting as it explored some of the policy side (e.g. family planning) of the population debate. Here is the video (Blogger wouldn't let me embed the video in the post for some reason so you'll have to do with the link!):

YouTube Video

Are Humans Overwhelming the Great Forces of Nature?

The above title is taken from an article by Steffen et al. (2007) where they discuss the existence of the Anthropocene as a new epoch characterised by human-driven changes to the Earth System. The authors of the study use atmospheric CO2 concentrations to track the ‘Anthropocene’ and determine whether humans have indeed had enough impact to “overwhelm the great forces of nature”.

What they found is that concentrations of CO2 in the atmosphere have risen from 279ppm (during the pre-industrial era) to 379ppm in 2005 (now the value is estimated to be 393ppm - co2now.org). This is significant due to the fact that concentrations had only been between 260 and 285ppm throughout the Holocene. Thus, they take the beginning of the Anthropocene to be the beginning of the 1800s. Others disagree, which we will look at another time, but anyhow the results show that humans have indeed had a significant impact on the Earth System. What we want to know now is the story behind it and how it links to the notion of overpopulation.

The story that is told is that we have always affected our surroundings, but this has evolved from localised impacts as hunter-gatherers (for example with the use of fire) to having impact on a global scale after the industrial revolution. During the late Pleistocene megafaunal extinction, although there are debates about the effect of climate, it is clear that humans had a role to play, through predation. When humans began domesticating, this was affecting their environment on a larger scale, although Steffen et al. maintain it wasn’t on a large-enough scale to alter the ‘great forces of nature’. The turning point, though, was the onset of industrialisation in the post-Enlightenment era.

Previously, economic and population growth were constrained by energy limitations. This was because wind and water power are only available in certain locations and under certain conditions; the energy from plants was limited by land area and also the inefficient conversion of light energy into chemical energy through photosynthesis (less than 1%). However, the invention of the steam engine in the 1770s and 1780s by Watt, coupled with the increased usage of fossil fuels shattered this bottleneck. The Haber-Bosch synthesis – which allowed for the synthesis of fertiliser out of atmospheric nitrogen) along with improved medical care meant that the population began to grow exponentially and along with it all the activities that increased CO2 production (refer to the graphs above). This trend has continued, unabated except for the Great Depression and the World Wars, until present day.

The main point I wanted to take from this article was that humans do have an impact on the environment; there is no doubt that, and the larger the human population, the larger the impact. Although Steffen et al. are implying that it is energy consumption, and economic growth that cause CO2 concentrations to rise, it follows logically that with less humans around, there would simply be less of the activities that impact the Earth System.

Sources: first and last set of diagrams; Haber-Bosch diagram