As much a feature of the 1980s as the smiley, acid rain was thought to be a problem that was going away. Now research indicates global warming is exacerbating old acid damage Not only are 1980s garish clothes and synthpop music back in fashion, but it seems the era's environmental problems are also returning to haunt us.
One of the first empirical studies to look at how global warming is affecting ecosystem health has found that the wet winters of recent years have hampered the recovery of streams from damage caused by acid rain decades ago.
We are going to find more and more cases where climate change exacerbates other forms of environmental degradation, says Peter Kareiva of US environment charity The Nature Conservancy.
"Previous achievements in environmental sustainability can be overturned when climate disruption piles on," he says. "There is a good chance that the climate's interactions with other environmental stresses may end up being the greatest risk we face, as opposed to the direct impacts of global warming."
Acid rain was one of the defining environmental issues of the 1980s, causing acid deposition in streams and rivers, making them uninhabitable for many species. But with increasing efforts to clean up sources of acid rain, acidity levels in the water had been steadily dropping.
Wet, wet, wet
Steve Ormerod and colleagues at Cardiff University in the UK have monitored the temperature and acidity levels of 14 Welsh streams - as well as the insects living there - for the past 25 years.
With the reduction in acid rain, they expected to see many insect species recolonising the streams. But their findings revealed that the aquatic ecosystems hadn't recovered as well as expected.
The researchers blame the recent increase in rainfall during the winter months. According to Ormerod, up to 40% of the last 25 years-worth of improvements have been cancelled out as a result of the recent weather changes.
"It looks as though wetter winter conditions are a problem, and given that the prediction is for rainfall volumes to go up by about 30%, there is this potential for knocking out recovery from things like acidification," he says.
Dead or alive
Increased rainfall reduces the buffering capacity of river systems by diluting base ions in the water and increasing acid ion input by increasing run-off from soils. "This is sufficient to push things in the acid direction again," Ormerod says. "So even though we've fixed an awful lot of the acid deposition problem, we still get the kind of acid episodes that are knocking out sensitive organisms."
Other environmental pollutants, such as nitrates are also affected by weather changes. In drought conditions, the flow volumes of rivers go down, and nitrates and other pollutants being discharged into rivers can have a greater ecological impact.
The spread of invasive species, sediment mobilisation, and the management of land use could all potentially be affected by climate change, says Ormerod. "Our work really emphasises that those predictions are being upheld," he says.
Experts told New Scientist that they are concerned that Ormerod's study might be just one example of a wider phenomenon where recent changes to the climate are exacerbating other environmental problems.
Crowded house
Tony Janetos, of the Joint Global Change Research Institute in Baltimore says there are many ways in which climate change can amplify existing environmental stress. For example, the rise in sea levels and the consequent rise in storm surges make the challenge of coastal erosion and property damage much more costly.
Also, "the expected increases in drought frequency in the western US make existing water management challenges more severe, and are already leading to an increase of wildfires and pest infestations in the regions forests - both of which have long-term implications for ecosystem integrity and economic impacts."
Ecologist Tim Seastedt of the University of Colorado says the warmer temperatures, combined with a longer growing season, elevated carbon dioxide concentrations, and higher inorganic nitrogen inputs are boosting the success of invasive species.
"This has expressed itself with the emergence of annual plants as significant cover components in our grasslands, something not seen in the past," he says. "Our native perennial species have not, to date, been able to keep up with these changes."
Seastedt says we need to be proactive in establishing desirable species in the appropriate habitats. "Just treating past problems is no longer sufficient," he says.
