AROUND A RECENT backyard bonfire on the outskirts of this small fishing and tourism town in the south-central part of Alaska, local residents debated whether a massive release of spruce pollen, which accumulated on every surface—including car bonnets, picnic tables and the nearby Kachemak Bay—amounted to a “golden sheen” or a “yellow scum”. The fine dust turned the surface of the sea the colour of butter and left a bright, lemony line on shore that marked the extent of high tide and gave off a sickly sweet smell. Eric Clarke manages trails at the nearby Kachemak Bay State Park, a rugged coastal area of dense spruce forests. He has been with the park for 24 years. “I haven’t seen a pollen dump like this in years,” he said. This huge release of pollen might be yet another symptom of a rapidly changing environment. Spruce pollen is made up of microscopic, double-lobed orbs that look a bit like Mickey Mouse heads. The “ears” are minute air sacks that help the pollen grains disperse over hundreds of miles, which in this region of Alaska means across mountains, glaciers and bays. Spruce trees release pollen annually, but every three to five years there is a natural bump in pollen prod...