A number of dangerous chemicals that have been frozen in the Arctic ice are being released as rising temperatures cause ice-caps to melt. The chemicals are called Persistent Organic Pollutants (or Pops) and include the industrial chemicals PCBs, and the pesticides DDT, lindane, and chlordane. They have all been banned under the 2004 Stockholm Convention due to the damaging effect they have on the environment and on human health. Studies carried out by Canadian and Norwegian scientists (the former based at Alert weather station in northern Canada and the latter at Zeppelin research station at Svalbaard) have shown that despite a global reduction in Pops emissions, air concentrations of PCBs and HCBs have been on the rise since 2004 due to chemicals being released from melting Arctic ice. Pops are stored in the fatty tissues of organisms that inadvertently consume them and are passed up the food chain because of this. Larger organisms at the top of the food chain, such as dolphins, seals, and orcas, therefore receive dangerously high concentrations of the chemicals that have profound effects on their health. In humans, Pops are related to cancers and physical deformity, among other defects and diseases. There is little scientific knowledge on the scale of Pops stored in high altitude regions.