Future Increases in Arctic Lightning and Fire Risk for Permafrost Carbon
Lightning is rare in the contemporary Arctic. Human infrastructure and ecosystems are not adapted to withstand the impacts of frequent lightning storms. In August of 2019 when the U.S. National Weather Service recorded lightning strikes within 300 miles of the North Pole, the story made national news headlines. Climate change may have a disproportionate effect on lighting in the far north because air temperatures are rising faster in this region than in any other region of the world. The warmer air also transports more moisture northward, creating the potential for unstable air masses, thunderstorms, and lightning during the summer months.
Our analysis suggests that lighting strikes will more than double in Arctic tundra ecosystems by the end of the century for a business-as-usual projection of climate change, causing the lightning regime to become comparable to what is currently observed in interior boreal forest ecosystems. Wildfires are common in boreal forests today, and our work suggests that the higher levels of lightning near and above the northern treeline will cause wildfires to become more common. The increase in wildfire has the potential to threaten carbon stored in permafrost soils and expedite northward migration of conifer trees, contributing to a well-established positive carbon-climate feedback. The projected changes in lightning flash rate in the Arctic are more than 3-fold larger than previous estimates for the CONUS.
Lightning is an indicator and a driver of climate change. Here, using satellite observations of lightning flash rate and ERA5 reanalysis, we find that the spatial pattern of summer lightning over northern circumpolar regions exhibits a strong positive relationship with the product of convective available potential energy (CAPE) and precipitation. Applying this relationship to Climate Model Intercomparison Project Phase 5 climate projections for a high-emissions scenario (RCP8.5) shows an increase in CAPE (86 ± 22%) and precipitation (17 ± 2%) in areas underlain by permafrost, causing summer lightning to increase by 112 ± 38% by the end of the century (2081–2100). Future flash rates at the northern treeline are comparable to current levels 480 km to the south in boreal forests. We hypothesize that lightning increases may induce a fire–vegetation feedback whereby more burning in Arctic tundra expedites the northward migration of boreal trees, with the potential to accelerate the positive carbon-climate feedback associated with permafrost soil carbon release.