The concept of "Planetary boundaries" was introduced by a group of scientists led by Johan Rockstrøm in 2009. It refers to the limits within which human activities can safely operate without causing irreversible damage to the Earth's systems and resources.
The nine planetary boundaries identified by Rockstrøm et al are climate change, biodiversity loss, land use change, freshwater use, ocean acidification, ozone depletion, atmospheric aerosol loading, chemical pollution, and the introduction of novel entities.
The planetary boundaries were determined through a combination of scientific evidence and expert judgment. The scientists analyzed various Earth systems and their interactions to identify the thresholds beyond which irreversible changes could occur. They also considered the potential impacts on human societies and ecosystems.
According to recent research, at least four of the planetary boundaries have been crossed - climate change, biodiversity loss, land use change, and the nitrogen cycle. This means that human activities have exceeded the safe operating limits for these boundaries, and urgent action is needed to prevent further damage.
To stay within the planetary boundaries, there needs to be a global effort to reduce greenhouse gas emissions, protect and restore biodiversity, reduce the use of land and water resources, and reduce pollution. This will require changes in individual behaviors, as well as systemic changes in our economic and political systems.