Biosphere Tipping Points

In this post, I aim to distinguish between arguments and propositions for global planetary scale ecological tipping points and local, sub-continental/regional tipping points and whether one causes the other.

Local vs Global

In true geography fashion, no issue is resolved without discussing scale. The majority of recent scientific studies have pointed to the presence of global, planetary scale climatic state shifts with catastrophic consequences, as epitomised by the planetary boundaries concept. However, questions have been raised on whether genuinely global tipping points are scientifically probable and whether non-climatic elements (eg. terrestrial and ecological systems) can have global scale tipping points. Listed below are main characteristics for planetary  tipping points:

1) The magnitude, extent and rates of present global forcings (human population growth, energy consumption, climate change) initiated by anthropogenic activities have surpassed global forcings which caused past global state shifts (Barnosky et.al.2012)

2) Planetary scale tipping points originate from the accumulation of local system behaviour where local scale forcings propagate through scales to cause global state shifts (Steffen et.al. 2011)

3) Planetary tipping points may not contain early warning signs or trajectory may be smoothed out despite impending critical thresholds (Scheffer et.al. 2009)

4) Internal evolutionary events causing changes on a global scale (Lenton and Williams 2013)

5) Global tipping points may not be synchronous or sudden. Internal inertia may cause incremental and gradual change relative to human timescales. Speed and abruptness should not be criterion for global tipping points (Hughes et.al. 2013).

While it is established that local ecological and biological systems have had tipping points, there have been substantial arguments against the presence of planetary scale thresholds:

1) Unlikely due to high spatial heterogeneity and low connectivity within regions of the biosphere. Global forcings unlikely to cause synchronous tipping due to spatial heterogeneity of and differing environmental impacts between local regions (Brook et.al. 2013)

• Eg. landscape fragmentation from the building of roads in which current roadless areas are fragmented into >600,000 patches at the expense of terrestrial biodiversity (Ibish et.al. 2016)

2) Most proposed planetary tipping points does not have genuinely global biophysical boundaries Global limits may limit local/regional action (Blomqvist et.al. 2012) 

3) Dichotomy thinking of 'safe' and catastrophic in planetary tipping points may encourage inaction and may distract from fundamental local regime shifts and biological change (Brook et.al. 2013)

In the next post, I will look at the possibility of an Amazon dieback. After that, I will conclude the blog by looking at present-day anthropogenic forcing.