New Delhi, Aug. 21 -- One way to be climate-friendly: Shop sustainably. But figuring out which products count as "sustainable" can be hard, especially when buying online.

As ordering with a computer or phone becomes more ubiquitous, the number of online products labeled sustainable is also increasing. Yet there is no single seal of approval across e-commerce platforms that verifies whether something is climate-friendly, partly because there are multiple ways to define sustainability.

Third-party nonprofit organizations study manufacturers and sellers' practices and offer certifications that are displayed online. Government programs such as the Agriculture Department's organic certification or Environmental Protection Agency's Energy Sta...