Geoscience Reference
In-Depth Information
Planetary limits
Climate change is but one of many global environmental problems that we currently face.
One way to understand the current state of the global environment is by using the idea of
planetary boundaries. This concept was proposed by a group of scientists led by Professor
Johan Rockström from the Stockholm Resilience Centre and Professor Will Steffen from
the Australian National University. In 2009, the group proposed a framework of 'planetary
boundaries' designed to define a 'safe operating space for humanity' for the international
community to understand and engage with. They proposed nine separate boundaries (see
Figure 39
). Humanity has already crossed what scientists feel is the acceptable boundary
for three of these (see
Table 6
). These include climate change as reviewed in this topic,
biodiversity loss which is currently 100-1,000 times the background rate and the disruption
of key biogeochemical cycles. For example, the early 20th century invention of the
Haber-Bosch process allowing the conversion of atmospheric nitrogen to ammonia for use
as fertilizer has altered the global nitrogen cycle so radically that the nearest geological
comparison are events ~2.5 billion years ago.The global phosphorus and sulphur cycles
have seen similar dramatic alterations. Of the other six boundaries, we are not yet at the
proposed boundary for four of them and scientists are unable as yet to define a boundary at
which two of them will become a planetary problem. The latter two include atmospheric
aerosols and chemical pollution. The concept of planetary boundaries has come under criti-
cism as it is very hard to define what a safety zone is within each theme and also there is no
current way to examine the interaction between the boundaries, for example the how cli-
mate change may effect biodiversity. But the concept of planetary boundaries is extremely
useful as it challenges the belief that resources are either limitless or infinitely substitut-
able. It threatens the business-as-usual approach to economic growth. As Professor Will
Steffen pointed out, the fact that reference to planetary boundaries was excluded from the
Rio+20 Earth Summit conference statement (2012) is, counterintuitively, a sign that the
concept is being taken very seriously and has indeed gained enough traction to be threaten-
ing to the status quo.
