Purpose: the carbon accounting standards library - ISO 14064 series, ISO 14067, ISO 14068-1, GHG Protocol and withdrawn standards such as PAS 2050, each with status, as-of date, issuer and confidence grade. Guidelines: use when a question involves which standard governs an organisation-level inventory, a product carbon footprint, or a verification statement; filter status='withdrawn' to check whether a standard still applies. Limits: standards catalogue only - no interpretation of how a standard applies to a specific company. Ex: get_carbon_standards(), get_carbon_standards(status='withdrawn'), get_carbon_standards(keyword='14067').