Scientists found climate change hidden in old military air samples

Air sampling in Sweden began in the 1960s as part of efforts to monitor radioactive fallout from nuclear weapons testing. At the time, the goal was strictly related to national security, not ecology. Yet the glass fiber filters used to trap airborne particles also preserved traces of DNA from pollen, spores, and other microscopic biological material. This unexpected scientific resource was identified by Per Stenberg, a researcher at Umeå University.

"The samples have proved to be an unexpected, unique and very exciting archive of DNA from wind-dispersed biological particles," says Nils Cronberg, a botany researcher at Lund University.

Moss spores are appearing weeks earlier than before

Using this archive, the research team tracked changes in airborne moss spores across a 35-year period, focusing on 16 different moss species and groups. Their analysis revealed a striking shift. On average, mosses now begin releasing spores about four weeks earlier than they did in 1990, and the peak of spore dispersal arrives roughly six weeks sooner.

"It's a considerable difference, especially considering that summer is so short in the north," says Nils Cronberg.

Last year's climate matters more than spring weather

The findings point to warmer autumns as a key driver of the shift. When autumn temperatures stay higher for longer, mosses have more time to develop their spore capsules before winter arrives. This extra development time gives the plants a biological kick-start, allowing spores to be released earlier once spring begins. One of the most unexpected results was what did not influence spore timing.

"We had expected that snow thaw or air temperature in the same year as spore dispersal would be crucial, but climate conditions the year before were shown to be the most important factor," says Fia Bengtsson, formerly a researcher in botany at Lund University, who is now at the Norwegian Institute for Nature Research.

A new way to track long-term ecological change

Beyond documenting rapid ecological responses to climate change, the study introduces a powerful new approach for studying how plants and animals have changed over time. The same DNA-based method can be applied to other species that release biological material into the air. Because air samples have been collected from locations across Sweden, researchers can reconstruct ecological shifts over decades and compare trends from north to south.

"We anticipate that our results and knowledge about how nature has changed from the 1970s onwards will be part of the next report by the Intergovernmental Panel on Climate Change (IPCC) on the documented effects of climate change," concludes Nils Cronberg.