Concluding post: land cover change in South America

Dear Readers! 

I hope you have enjoyed this blog as much as I have enjoyed writing it!

South America is a large and diverse continent - and for the purpose of this blog I have mostly concentrated on its northern half, especially the Amazon area and immediate surrounding. I chose this focus due to the global significance of the Amazon rainforest in its share of terrestrial biodiversity, role in the hydrological and carbon cycle and global climate circulations. 

Through this blog, I tried to highlight the current land cover of South America and the pressures that exist on its conversion or amendment for human purposes. Posts discussed different ways in which forest resilience is interrupted or reduced, followed by a detailed assessment of the wider effects of land cover change with a special focus on the most dominant mode: rainforest to pasture conversion. The effects covered were the quite obvious reduction in biodiveristy, the two-fold impact on renewable surface water formation, the complexity of climatic effects (local, regional and global) and the role of forests and deforestation in the carbon cycle.

It is important to assess the way anthropogenic land-cover change is caused, reinforces and also interacts with the effects of global climatic change. Consequences are severe for both natural ecosystem health and the human populations within the suggested area - if I would continue this blog further, I would expand on the socio-economic perspective as well.

I believe that this blog topic has helped me manifest my understanding of the complex manner in which humans are morphing the planet, and has put this knowledge into the context of the 9 planetary boundaries. As shown throughout my blogging, quite interestingly, a spatially limited phenomenon such as land cover change in South America impacts the situation of the whole planet not only within the boundary of 'land-system change' but also in others. Those covered here were mainly influencing 'biogeochemical flows', 'biosphere integrity', 'climate change' and 'atmospheric aerosol loading'. Thus my topic felt well-chosen to highlight the tight interactions of entities within the Earth system contributing to 'Global Environmental Change'. 

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The inclusion of land cover change in future climate projections

Global circulation models all, but to a different extent, include land cover change scenarios when predicting future climates. Feddema et al (2005) analysed how important it is to include these for the outcome of the modelling.

The study shows that the way human will choose to alter the land cover in the future will have important effects on the real impact of climate change on the Earth. While on a global scale, land cover changes are expected to even out in their effects on global mean temperature and the hydrological cycle. The biogeochemical and biogeophysical effects of land cover change will, however, have modulating effects on the regional scale response to climate change. This supports my analysis of the effect of land cover change on climate in my previous posts. 

The characteristics of expected future land cover change is shown in the mapping of the IPCC SRES land-cover projections (Figure). We can see that significant changes are expected to occur in South America in all scenarios by 2050, mostly focused on Western Amazonia, South-Eastern Brazil and the southern tip of the continent. The most common change is the conversion to cool/warm grass land for agricultural purposes and livestock farming. The expected drying of the continent is reflected in the spreading of savannah biomes. What I find interesting is that in the B1 emission scenario, little change is expected in the central Amazon by 2050 and 2100 (see the boxed region on South America) - this may suggest that the rainforest conservation strategies implemented (both national and international along the lines of REDD) are expected to be effective and/or that the rainforest is able to withstand the adverse effects of global climate change.

Figure, (Source)

A new way to make CO2 emission estimates from deforestation more reliable - a step forward for policy implementation?

There are limited studies that exist detailing the emissions arising from a certain land cover changes. So the IPCC shows in their "land-use change" category of SRES category desciptions, that all estimates of emissions from land-use change are calculated based on the obtainable deforestation and afforestation figures. Further, these are based on estimates from the expected carbon storage of a set area of forest. 
In 2012, Harris et al produced a baseline map of carbon emissions in tropical regions, using satellite imagery. Pairing deforested regions of interest with the carbon stock before clearing (using base map) can help with the evaluation of CO2 emissions and the reaching of conservation targets.



The map above is taken from the publication. "Distribution of annual carbon emissions from gross forest cover loss between 2000 and 2005 mapped at a spatial resolution of 18.5 km."

Despite the lowering of deforestation rates (highlighted in my first posts) in South America, it is still high to the extent of emitting 5-200 Gg of Carbon per year between 2000-05. Of course the higher end of this spectrum is only realistic for a few Amazonian regions but should still highlight the importance of tackling this problem. If deforestation effects on the local biodiversity and climate are not enough to power strict management policy implementation, maybe the visualisation of CO2 emissions is!

The uncertain, but changing, potential of the terrestrial biosphere as a future carbon sink

I am aware that the studies used in this post are not directly linked to the South American continent as such but I consider it interesting to cover the topics due to the large proportion of the global terrestrial carbon sink lying within South America.

As described in my previous post, forests have and had the potential to store large amounts of carbon. In fact many studies now agree (e.g. A, B,) that carbon uptake by natural sinks has increased over time. The reason for this is a physiological vegetation response to CO2 fertilization in the atmosphere, that increases plants' primary productivity and thus increases the carbon stored per hectare of intact forest. Ballantyne et al (2012) use a global scale CO2 mass balance analysis to show the evolution of the carbon budget 1959-2010. 

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While fossil fuel emissions have been pumping CO2 in the atmosphere at an alarming rate, there is a clear increase in CO2 from the atmosphere to global sinks over the same course of time. It mirrors the atmospheric concentration - it is a dynamic response, which means that "terrestrial ecosystem carbon fluxes both respond to and strongly influence the atmospheric CO2 increase and climate change". In a modelling study by Cao and Woodward (1998), we can see that we are still in a period in which the CO2 fertilization effect is strong enough to uphold a net positive relationship between emissions and sinks, however in the future as the effect becomes saturated a leveling off of potential terrestrial sinks is expected. Cox et al (2000) even suspect that post 2050 climate change will have such altering effects that terrestrial sinks will turn to sources (and this projection does not even take anthropogenic deforestation into account yet but is purely based on climate change effects!)

Now going back to land cover change directly: a carbon dioxide removal (CDR) technique of geoengineering is the afforestation of previously converted landscapes. This way, carbon is sequestrated from the atmosphere and stored in the new-grown forests. Fellow blogger Maria Christofi has reviewed the potential for this method in elevating dangerous levels of CO2 in the atmosphere at: http://geoengineeringinquiries.blogspot.co.uk/. A question that arises to me now is whether the negative feedback loop that has been described by Cox et al (2000) renders this method useless in the future? The uncertainty regarding the vegetation-climate responses of the future definitely adds to the factors needed to consider before intervening further with land-cover changes.