Lead pollution may have kept climate cooler, study suggests
Lead particles in the atmosphere have been boosting cloud formation, a new EU-funded study reveals. Writing in the journal Nature Geoscience, the researchers suggest that atmospheric lead pollution may have dampened the effects of climate change in recent decades. EU support for the research came from the 'Atmospheric composition change' Network of Excellence, which is financed under the 'Sustainable development, global change and ecosystems' Thematic area of the Sixth Framework Programme (FP6). Most of the lead in the atmosphere comes from human activities; top sources are coal burning, leaded petrol, small planes flying at the altitude where clouds form, and construction work that frees lead from the ground. While greenhouse gas emissions cause global warming, the emission of small particles of substances like lead can have the opposite effect by interacting with water vapour in the atmosphere to trigger the formation of clouds. Depending on their altitude and thickness, clouds can either reflect sunlight back into space or trap warmth from the Earth. The aim of this latest study was to determine the impact of this lead on cloud formation. To do this, scientists in Germany, Switzerland and the US 'captured' real clouds from mountaintops on either side of the Atlantic and studied clouds created artificially in special cloud chambers in the laboratory. Their investigations revealed that lead changed the conditions needed for clouds to appear: when lead is present, the air does not have to be as cold or humid for clouds to form. Furthermore, computer models demonstrated that lead-containing particles change the properties of clouds enough to influence the amount of long-wave radiation that escapes from the Earth. During the 1970s and 1980s, before the widespread introduction of lead-free petrol, most of the dust particles floating in the atmosphere were probably contaminated with lead, allowing more heat to escape from the Earth. 'This probably led to a global inhibition of rises in temperature to some extent, whereas today almost the full greenhouse effect is kicking in,' explained Professor Joachim Curtius of Goethe University Frankfurt in Germany. Few would advocate pumping more lead into the atmosphere to counter the effects of global warming, as it is a highly toxic metal that is harmful to human health. 'However, with the benefit of hindsight we can now explain why there has been a trend towards more rapid temperature rises in recent years; it is because mankind has cut back its emissions of lead and sulphates,' said Professor Stephen Borrmann of Johannes Gutenberg University of Mainz, Germany. 'We know that the vast majority of lead in the atmosphere comes from man-made sources,' commented lead author Dan Cziczo of the US Department of Energy's Pacific Northwest National Laboratory. 'And now we show that the lead is changing the properties of clouds and therefore the balance of the sun's energy that affects our atmosphere.'
Countries
Switzerland, Germany, United States