Johan Rockström's Planetary Boundaries Model is a valuable tool to assess the state of nine earth systems. According to their most recent analysis in 2015, which two systems are in the danger zone?

According to the 2015 analysis of Johan Rockström's Planetary Boundaries Model, four Earth systems were identified as being in the "danger zone" (transgressed boundaries):

• Climate Change
• Biosphere Integrity (both genetic and functional diversity)
• Biogeochemical Flows (nitrogen and phosphorus cycles)
• Land-system Change

Let's evaluate the given options:

• Biogeochemical Flows and Biosphere Integrity: Both of these systems were transgressed in 2015.
• Climate Change and Biogeochemical Flows: Both of these systems were also transgressed in 2015.
• Climate Change and Ocean Acidification: While Climate Change was transgressed, Ocean Acidification was identified as approaching the boundary, not yet in the danger zone, in 2015.
• Freshwater Use and Sea Level Rise: Freshwater Use was approaching the boundary, and Sea Level Rise is a consequence of climate change, not one of the nine primary planetary boundaries itself.

Both "Biogeochemical Flows and Biosphere Integrity" and "Climate Change and Biogeochemical Flows" contain two systems that were in the danger zone in 2015. However, Climate Change is consistently highlighted as one of the most critical and widely recognized transgressed boundaries. Therefore, the option including Climate Change is often considered a primary correct answer.

The correct option is B.

B) Climate Change and Biogeochemical Flows