ECVs are required to support the work of the United Nations Framework Convention on Climate Change (UNFCCC) (link is external) and the Intergovernmental Panel on Climate Change (link is external). All Essential Climate Variables are technically and economically feasible for systematic observation. It is these variables for which international exchange is required for both current and historical observations. It is emphasized that the ordering within the table is simply for convenience and is not an indicator of relative priority.