Full Mixed Practice Test

AThe concept of 'planetary boundaries' — a framework for defining the safe operating space for humanity on Earth — was introduced by a team of scientists led by Johan Rockström in 2009. The framework identifies nine Earth-system processes that regulate the stability and resilience of the planet: climate change, biosphere integrity, land-system change, freshwater use, biogeochemical flows, ocean acidification, atmospheric aerosol loading, stratospheric ozone depletion, and novel entities (such as synthetic chemicals and plastics). The scientists proposed quantitative boundaries for each process, beyond which the risk of abrupt or irreversible environmental change increases significantly.

BThe planetary boundaries framework has been updated several times since its introduction. A 2023 assessment found that six of the nine boundaries had already been transgressed, including climate change, biosphere integrity, land-system change, freshwater use, and biogeochemical flows. The authors expressed particular concern about the boundary for biosphere integrity — which encompasses both the genetic diversity of species and the functional role of organisms in ecosystems — arguing that the current rate of species extinction is so far beyond the safe boundary that it represents an existential threat to the stability of the Earth system.

CCritics of the planetary boundaries framework have raised several objections. Some scientists argue that the boundaries are inherently arbitrary, since the Earth system does not operate according to simple thresholds but rather through complex, non-linear dynamics that make precise boundary-setting impossible. Others contend that the framework is too focused on global averages and fails to capture the highly uneven distribution of environmental pressures across different regions and communities. A further criticism is that the framework does not adequately address the social dimensions of sustainability — in particular, the question of how the benefits and burdens of staying within planetary boundaries should be distributed equitably among different countries and populations.

DDespite these criticisms, the planetary boundaries framework has had a significant influence on international environmental policy. It has been incorporated into the United Nations' Sustainable Development Goals and has informed the development of the Kunming-Montreal Global Biodiversity Framework, which sets a target of protecting 30% of the world's land and ocean areas by 2030. Several national governments have also adopted the framework as a basis for their environmental planning, and it has been widely used by businesses seeking to assess and reduce their environmental impact.

EThe relationship between planetary boundaries and human wellbeing is complex. Staying within planetary boundaries is a necessary condition for long-term human prosperity, but it is not sufficient: even within the safe operating space, billions of people currently lack access to adequate food, clean water, healthcare, and education. Some researchers have proposed the concept of a 'safe and just space for humanity' — sometimes visualised as a 'doughnut' — which combines the planetary boundaries ceiling with a social foundation floor, defining the space within which all people can live well without exceeding the Earth's limits. This framework, developed by economist Kate Raworth, has been adopted by several cities and organisations as a guide for sustainable development.