For which of the following planetary boundaries have no quantitative indicators been presented yet?

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When evaluating which planetary boundaries lack presented quantitative indicators, we should assess the status of each option against the knowledge of planetary boundary indicators.
Option a: Chemicalisation of the environment. This choice refers to the broad accumulation of synthetic chemicals and related pollutants in ecosystems. Historically, this boundary has been noted as lacking a comprehensive, globally agreed-upon quantitative indicator set, making it a plausible candidate for having no quantitative indicators presented yet. The complexity and diversity of chemicals, exposure pathways, and effects complicate standardized measurement, which supports why a single universal indicator has not been established.
Option b: Ocean acidification. In contrast, there are well-defined quantitative indicators for ocean acidification, such as the aragonite saturation state (Omega aragonite) and pH levels of seawater, which are tracked globally and used in policy discussions. Thus, this option is not the correct choice for "no quantitative indicators".
Option c: Changes in land use. This boundary has quantitative indicators like net land-use change area, land-system change, and related metrics derived from satellite observations and land-cover classifications. Therefore, there are established quantitative indicators for changes in land use, so this option is unlikely to be the one with no quantitative indicators.
Option d: Climate change. Climate change has abundant quantitative indicators, including global mean surface temperature rise, atmospheric CO2 concentration, radiative forcing, and various emissions metrics. Hence, this option also does have quantitative indicators in place.
In sum, among the listed boundaries, chemicalisation of the environment stands out as the one with the least settled, globally standardized quantitative indicators at present, due to the wide diversity of chemicals, exposure scenarios, and effects that resist simple aggregation into a single metric. The other options are supported by concrete, widely used quantitative measures that track changes over time.

BH60A6801 Sustainable.now - Online teaching (3 cr) 3.3.2025-20.4.2025 QUIZ (English)

For which of the following planetary boundaries have no quantitative indicators been presented yet?

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