As United Nations delegates end their mercury treaty talks today, scientists warn that ongoing emissions are more of a threat to food webs than the mercury already in the environment. At the same time, climate change is likely to alter food webs and patterns of mercury transport in places such as the Arctic, which will further complicate efforts to keep the contaminant out of people and their food. The discovery that new mercury seems to be more of a threat than old mercury could add impetus for reducing global emissions. “For ocean fish and people eating them, it may take decades to see the benefits,” said Noelle Selin, a professor at the Massachusetts Institute of Technology. “But without a treaty, things are only going to get worse.” An increase equivalent to about one-quarter of the 2005 human-caused mercury emissions, or about 500 tons per year, is expected by 2020 if there are no major changes.