A new study finds that low Arctic sea ice levels during July to October have knock-on impacts in the atmosphere that push the jet stream northwards. This tends to bring hotter and drier conditions in the western US over the following autumn, resulting in more frequent and intense fires in the region.
They say that this mechanism may strengthen over the coming decades as the Arctic melts furthur, making the western US “even more susceptible to destructive fire hazards”.
A separate study finds that extreme wildfire activity has increased globally over 1979 – 2020 mainly driven by decreasing humidity and increasing temperatures.
While arctic sea ice and fire activity in the western US may seem unrelated, a new study – using a range of observations, sensitivity test and targeted model runs – suggests that they are linked through a pattern of large-scale atmospheric pressure and circulation changes called a “teleconnection”.
The study found that low levels of Arctic sea ice in the summer and autumn means the region reflects less of the sun’s incoming radiation, leading to stronger surface warming. A warmer surface means greater heating of the air directly above it, which then rises through the atmosphere.
The “teleconnection”describes the knock-on impact this has in the atmosphere, which shifts the jet stream further poleward and causes “suppressed precipitation and elevated surface air temperature and vapour pressure deficit over the western US”, the authors say.
The jet stream is a current of fast-moving air high up in the troposphere, which separates cold polar air to the north from warm tropical air to the south. A poleward shift in the jet stream changes weather patterns in the western US by suppressing rainfall and bringing in warmer temperatures, the paper says.