AC transmission: Impact on the biosphere

Bird strikes, wildfires and a gas 24,300 times worse than CO2

What this tab covers Effects on human, animal, plant, fungal and microbial life and on whole ecosystems: in the short term (construction and early years), medium term (operating life) and long term (decommissioning and legacy).

Overhead AC lines take land, kill birds by collision, can start wildfires and leak a potent greenhouse gas from switchgear. Any effect of their magnetic fields on human health is uncertain and, if real, weak.

Bird deaths from power-line collisions, US 8 to 57 million a year¹⁶ Camp Fire, California, 2018 85 deaths, 18,804 structures destroyed, 153,336 acres burned¹⁸ Magnetic field level in leukaemia studies Above about 0.3 to 0.4 microtesla (time-averaged); IARC class 2B since 2002¹⁷ SF6 global warming potential 24,300 times CO2¹⁹

Effects over time

Life affected	Short term	Medium term	Long term
Humans¹⁷¹⁸	Construction traffic, noise and land disputes along new corridors	Wildfire risk where lines fail in dry, windy weather (PG&E transmission lines caused the 2018 Camp Fire, which killed 85 people); low-frequency magnetic fields, with a weak, unproven statistical link to childhood leukaemia above about 0.3 to 0.4 microtesla	Corridors constrain land use for decades
Animals¹⁶	Disturbance during tower and access-road building	Power lines of all voltages kill an estimated 8 to 57 million birds a year by collision in the US	Collision risk lasts as long as the line stands; marking lines reduces it
Plants	Clearing of trees along the right of way	Repeated vegetation cutting keeps corridors as grass or shrub	Little evidence of effect
Fungi and soil life	Soil compaction at tower foundations and access tracks	Little evidence of effect	Little evidence of effect
Ecosystems¹⁹	Fragmentation where corridors cut through forest	SF6 leaking from switchgear has a global warming potential of 24,300	Little evidence of effect

How the effects are reduced

Routing lines away from forests and wetlands and reusing existing corridors (reconductoring) reduce land take. Markers on earth wires make lines more visible to birds. Utilities in fire-prone areas clear vegetation, harden equipment and switch lines off in extreme fire weather. The EU is phasing out SF6 in new switchgear by voltage class between 2026 and 2032.

Sources

Refining estimates of bird collision and electrocution mortality at power lines in the United States (Loss, Will and Marra) PLOS ONE (abstract via RePEc/IDEAS), 2014
WHO risk assessment of low-frequency fields German Federal Office for Radiation Protection (BfS), 2024
CAL FIRE investigators determine cause of the Camp Fire (CAL FIRE news release, reproduced by PreventionWeb) CAL FIRE via PreventionWeb (UNDRR), 2019
Transition to SF6-free electrical switchgear will begin in 2026 Finnish Environment Institute (Syke), 2025