Geoscience Reference
In-Depth Information
●
ocean acidification (mean surface seawater saturation state with respect to
aragonite ≥ 80 per cent of pre-industrial levels);
●
stratospheric ozone (<5 per cent reduction in O
3
concentration from
pre-industrial level of 290 Dobson Units);
●
biogeochemical nitrogen (N) cycle (limit industrial and agricultural fixation
of N
2
to 35 Tg N yr
2
1
) and phosphorus (P) cycle (annual P inflow to oceans
not to exceed 10 times the natural background weathering of P);
●
global freshwater use (<4000 km
3
yr
2
1
of consumptive use of runoff resources);
●
land system change (<15 per cent of the ice-free land surface under cropland);
●
rate at which biological diversity is lost (annual rate of <10 extinctions per
million species);
●
chemical pollution (not yet quantified);
●
atmospheric aerosol loading (not yet quantified).
aries that have been quantified compared to the 'safe operating space', which is
shown in the centre of the Figure as the lightly-shaded circle. It is estimated that
humanity has already transgressed three planetary boundaries: those for climate
change, rate of biodiversity loss, and changes to the global nitrogen cycle.
The important point is that climate change is affecting a planetary life support
system that is already under other stresses, such an excess loading of nitrogen,
and is suffering an erosion of resilience through the loss of biological diversity. In
addition to these environmental stresses, however, it is important to remember
that changes in the socio-economic sphere are just as important for the types of
compounding global crises described in this chapter.
As indicated earlier there is increasing evidence that the natural Earth System
behaves as a single interacting system. However, this is also increasingly the
case for our modern society as a whole. Things that at first glance appear not
to be connected, such as the economic system, population and ageing, ores and
mineral production, conflict and terrorism, energy production and social systems,
at closer inspection are all part of an intricate web where changes in one of these
elements has knock-on effects on another element, which in turn impacts on yet
another element, and so on. To add even further to the complexity, all of these
are also connected to and interact with the natural system.
To give just one example, increases in the frequency and magnitude of extreme
weather events, such as floods, droughts, wind storms, tropical cyclones etc., are
expected as a result of climate change (IPCC, 2007a; 2012). The impacts of these
extreme events will be most severely felt in developing countries (IPCC 2007b;
2012).
There are several reasons why this will be the case. For instance, impacts are
worse - many developing countries are already more flood and drought prone and
a large share of the economy is in climate sensitive sectors. Also, many devel-
oping countries have a high level of vulnerability and a weak ability to adapt to
existing and emerging climate-related pressures because of their lack of financial,
institutional and technological capacity and access to relevant knowledge.
