During the industrial boom of the mid-twentieth century thousands of man-made chemicals were created to make chemical processes and products stronger and more durable.
The substances became useful in pest control and crop production, but it wasn't long before they also proved deadly, causing cancers, birth defects and other health problems.
Known as persistent organic pollutants (or POPs), this group of the world's most toxic compounds takes decades to degrade as they circulate through Earth's oceans and the atmosphere, gradually accumulating in the fatty tissues of humans and wildlife.
Once the connection between POPs and toxicity was scientifically proven, wealthy governments sprang into action to reduce the risks, eventually restricting or banning the use of 12 pollutants, including DDT and polychlorinated biphenyls (PCBs), at the 2001 .
Climatic forces were also helping to limit the chemicals' global reach.
In places like the Arctic, cold temperatures trapped POPs in snow, soil and oceans capped by sea ice, as the long-lived pollutants circled through the region. Between the POPs settling into the Arctic and other sinks — and the international campaign to regulate the chemicals — atmospheric levels of POPs steadily declined during the past decade.
New research, however, suggests that global warming is reversing this downward trend.
Climatologists at , the Canadian environmental agency, found that as climate change heats up oceans and melts sea ice and snow, the buried pollutants, known as legacy POPs, are being re-released back into the atmosphere.
This could undermine international treaties to restrict production and importation of the high-risk toxics and human exposure to them, the scientists say.
The research was published online yesterday in the ahead of print publication.
First to Make Warming Link
Over the years, various studies have indicated that a decrease in production of POPs due to regulation would result in lower levels of the toxics in the environment. This new paper was the first to consider whether climate impacts, like the melting Arctic, might be throwing a wrench into that assumption.
"An annoying feature of contaminant work in the Arctic in the early 2000s was that there was this notion of direct connectivity between the emissions controls [of POPs] and environmental exposure [to them]," said , a systems scientist at the , a division of Fisheries and Oceans Canada, who was not involved in the study.
"If you had a stable world, you could linearize everything," he explained. "But the problem is that the Arctic is changing rapidly. This paper is one of the first times scientists have actually put together a set of coherent data and looked at the trends responsibly in terms of how the [climatic] system is changing."
Macdonald said the research is key to developing more accurate ways to monitor the effectiveness of toxics regulation, such as the Stockholm Convention, especially since most governments and scientists only use linear atmospheric trends to measure whether chemicals policy is working.
The study, which was inspired by recent research, suggests that these trends have to be looked at in the context of changing ecosystems from global warming.