बर्फ की चादरों (ice sheets) के पिघलने के कारण प्रत्यक्ष रूप से कौन-सी वैश्विक पर्यावरणीय समस्या उत्पन्न होती है?

Prolonged exposure to extreme cold temperatures may result in tissue damage known as frostbite, which is categorized as a:

In the context of ecosystem energy dynamics, which of the following expressions correctly defines Net Primary Productivity (NPP)?