The increase in lightning strikes in the Arctic, a source of climatic excesses?

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While the north polar zone is warming two to three times faster than the global average, transformations as rapid as they are varied are affecting the region. In this regard, the evolution of thunderstorm phenomena raises growing concerns. Among them, the risk of seeing lightning triggering amplification loops, as detailed in a study published in Nature’s climate change on April 5.

In a recent article, we discussed the significant increase in lightning strikes beyond the 60th parallel north over the past ten years. Observations testifying to an eight-fold increase in the number of electric shocks, which rose from 18,000 in 2010 to more than 150,000 in 2020. However, this observation based on the study of a period that is all in all quite short and very recent work is now supplemented by work on future developments.

A future change in the continuity of recent observations

By assessing climate projections at the scale of the century, the new study makes it possible to better isolate the share of increase due to global warming. Indeed, from decade to decade, trends can be significantly modulated by natural variability. Let us cite in particular the fluctuations which bring into play the ocean-atmosphere couple (ENSO, I LIKE, etc.).

We projected how lightning will change in North America and Eurasia in the high latitude boreal forests and arctic tundra regions. “, Reports Yang Chen, lead author of the paper. ” The magnitude of the lightning response surprised us as the expected changes at mid-latitudes are much smaller “.

Variation (in%) of the number of lightning in 2080-2100 compared to 1986-2005. The percentage is calculated over May-August, where most of the thunderstorms are concentrated. Credits: Yang Chen et al. 2021.

Although the models do not represent lightning as such, it is possible to infer the statistic by evaluating other variables actually represented. Thus, by combining satellite measurements, reanalyses and numerical simulations in the case of a laissez-faire scenario, the researchers show that the number of lightning strikes would increase by 112% at high northern latitudes by the end of the century. The arctic region becoming an area more conducive to thunderstorm convection. In particular at the level of the Russian and Scandinavian continental margins.

Lightning-influenced amplification loops

The results obtained are far from being anecdotal. Specifically, the authors argue that an increased number of arctic lightning discharges could feed positive climate feedback loops (amplifiers). Indeed, once burned, the grasses, mosses and other shrubs of the tundra no longer play their role of barrier which prevents the seeds of trees coming from the south to take root. In fact, southern species would gain ground while limiting the amount of solar radiation reflected back to space – their albedo being lower than that of the steppes – which would warm the region even more.

In addition, the soil being less isolated, carbon could escape more easily into the atmosphere. In summary, by increasing the wildland fires they allow, lightning has the ability to induce a northward expansion of boreal forests and increased release of carbon from permafrost.

arctic lightning
Schematic representation of the described feedback loops. The dotted lines mark the indirect influence of lightning on the feedback loop between carbon, permafrost and warming. Credits: Yang Chen et al. 2021.

In Alaska, 2015 was an exceptional year of fires due to a record number of fires ”, Notes James Randerson, co-author of the study. ” One thing that got us thinking is that lightning was responsible for the record number of wildfires.“. A set of processes so far little studied in the context of Arctic warming and which will undoubtedly focus new research efforts in the years to come.

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