Planetary Boundaries & Climate Change

Planetary boundaries

Nine continental Earth system limits that define a safe operating space for humanity to maintain a stable planet and avoid abrupt, irreversible environmental change.

Current extinction rate relative to natural background rate

Species are currently becoming extinct at approximately $1{,}000$ times the natural background rate, primarily driven by habitat loss, overexploitation, pollution, and climate change.

Land use change impacts since the 1960s

Approximately $20\%$ of global forest cover has been lost, and about $55\%$ of Earth's ice-free land is now converted for agriculture and human settlements.

Novel entities

A planetary boundary formally assessed in 2022 that encompasses synthetic chemicals, plastics, industrial compounds, and other artificial materials released into the environment.

Atmospheric $\text{CO}_2$ safe boundary vs. current level

The safe operating threshold is proposed at $\sim 350\,\text{ppm}$, whereas current concentrations have reached approximately $420\,\text{ppm}$.

Climate tipping points

Critical thresholds in Earth's climate system that, once crossed, trigger abrupt and irreversible large-scale environmental transitions (such as the collapse of the West Antarctic Ice Sheet).

The Anthropocene

A proposed geological epoch characterized by significant, pervasive human transformation of Earth's climate, ecosystems, and sedimentary systems.

The Great Acceleration (1945)

A post-World War II period marked by exponential increases in human population, industrial activity, carbon emissions, and global resource exploitation.

Doughnut Model (Raworth, 2017)

A sustainable development framework where humanity thrives between an inner social foundation (meeting basic needs) and an outer environmental ceiling (respecting planetary boundaries).

Observed temperature warming in Australia

Australia's national average temperature has increased by approximately $1.47\,^\circ\text{C}$ since records began, lengthening fire seasons and raising extreme heat event frequency.

Ocean heat absorption share

The proportion of excess planetary heat absorbed by the oceans, currently quantified at approximately $91\%$, which accelerates marine heatwaves and coral bleaching.