Large amounts of carbon dioxide emitted by chemicals used increasingly in air conditioners, refrigerators, fire-fighting equipment and insulation foams could undermine efforts to keep global temperature rise under two degrees Celsius this century, according to a report released by the United Nations Environment Programme (UNEP).

The chemicals, collectively known as hydrofluorocarbons (HFCs), are becoming popular as replacements for those phased out or being phased out to protect the ozone layer – Earth’s atmospheric shield that filters out dangerous levels of the sun’s ultraviolet rays.

The UNEP study projects that by 2050 HFCs could be responsible for emissions equivalent to 3.5 to 8.8 gigatonnes (Gt) of carbon dioxide, comparable to total current annual emissions from transport, estimated at around six to seven Gt annually.