Since the turn of the millennium, devastating heat waves – known as blobs – have repeatedly occurred in the north-eastern Pacific off the west coast of North America. The most recent event to date lasted three years from 2019 to 2021 and cost the lives of tens of thousands of whales, seabirds and seals. A team led by Armineh Barkhordarian from the University of Hamburg has investigated this phenomenon. In »Nature Communications Earth and Environment«, it presents the cause of the increasing warm-water bubbles in the region: human-induced climate change.
The blob, which can be up to three million square kilometers in size, is due to the human-caused increase in greenhouse gases in the atmosphere, which favors extreme heat waves in this part of the sea, the working group writes. The water temperatures are then up to six degrees Celsius above the long-term average, which is fatal for many cold-loving animal species or forces them to migrate. The warm water also promotes toxic algae blooms, which, when they die, also remove oxygen from the water and thus harm or kill many living beings.
According to the analysis by Barkhordarian and Co, the probability that such a heat wave as between 2019 and 2021 would have taken place without human influence is less than one percent. There is a 99 percent probability that the increase in greenhouse gases in the atmosphere and the resulting global warming are responsible. Accordingly, the water temperature in the north-east Pacific has increased by an average of 0.05 degrees Celsius per year over the past 25 years. At the same time, the region cools less in winter due to less cloud formation and the period of summer conditions increased by 37 days. In winter, the high pressure areas over the water have intensified, making cloud formation more difficult. The undisturbed solar radiation can thus warm the sea during the day. This effect is obviously stronger than the nocturnal heat radiation that would otherwise be impeded by the clouds.