Write in short about ecosystem services and their valuation.

Ecosystem Services and Their Economic Valuation:

1. Four Tiers of Ecosystem Services (Millennium Ecosystem Assessment, 2005):
   • 1. Provisioning Services: Harvestable biological goods—freshwater, timber, crops, medicinal biomass.
   • 2. Regulating Services: Carbon sequestration, climatic stabilization, flood buffering by wetlands, and crop pollination.
   • 3. Cultural Services: Ecotourism, recreational, spiritual, and aesthetic enrichment.
   • 4. Supporting Services: Foundational pedogenesis (soil formation), biogeochemical nutrient cycles, and primary photosynthesis.
2. Economic Valuation: Robert Costanza et al. (1997) quantified global ecosystem services at an estimated $33 Trillion annually (nearly double the aggregate Global GNP at the time), underscoring the economic indispensability of nature.