ARI SHAPIRO, HOST:
Storms this year have caused massive blackouts, showing just how challenging and dangerous life can get when people lose electricity. It's not just big storms driving outages. Hotter temperatures are also damaging trees, making them more likely to fall on power lines. Julia Simon reports.
IGOR LACAN: I have my hat because the sun is bright.
JULIA SIMON, BYLINE: On a hill in Oakland, Calif., horticulture adviser Igor Lacan looks out from under his Stetson hat at the neighborhood below - a bunch of trees amidst a web of power lines.
LACAN: Maples, to birches, to plums, to liquid amber. And you've got a monkey puzzle up here. And look; it's growing cones. Look...
SIMON: These trees are flourishing, but not some nearby acacias. Lacan points out an eye-shaped hole in one trunk.
LACAN: It's sort of a wound that doesn't heal. That's a good indication that there's something going on.
SIMON: Lacan says a fungus is killing these trees. California's climate-change-fueled drought left them vulnerable. Lacan works at University of California Cooperative Extension. He says dying trees like this can topple onto power lines and cause fires or outages. He works with utilities to spot sick trees before that happens. He points up at a branch.
LACAN: The bark coming off - if you can see the wood underneath, which in this case you can, that's typically a sign that that part of the tree is dead, which is why we didn't stand under that branch.
SIMON: More than a dozen of the country's largest utilities told NPR that falling trees are a leading cause of outages. A patchwork of national and state regulations require utilities to trim around their power lines. But as more trees suffer from climate-related stresses...
SEAN REDDING: There are more than we can manage in a timely manner.
SIMON: Sean Redding is vegetation manager for Eversource Utility in Connecticut. More than a million people lost power in a heat wave there after last summer's Tropical Storm Isaias. He says researchers found areas with drought-weakened trees experienced more outages.
REDDING: Because of the cumulative effect of climate change, the damage was worse. More trees came down, resulting in more outages and more broken poles.
SIMON: David MacFarlane at Michigan State University sees another climate threat - increased rainfall intensity. In a summer deluge, the softened soil plus branches full of wet leaves make trees more susceptible to falling over, especially in wind.
DAVID MACFARLANE: The combination of both water and wind working together against the trees - and those are direct climate effects.
SIMON: Jamie Kryscynski is tree trim manager for Michigan's largest utility, DTE Energy. When he ventured out near Detroit after a severe July storm, he was in awe of the storm's power. Some of the largest trees were all over the power lines.
JAMIE KRYSCYNSKI: Trees like oaks - oaks, they're very strong trees. Like, they're one of the strongest trees out there. And we had oaks that just snapped.
SIMON: It's not just fungi, drought and storms. Shorter and warmer winters lead to all kinds of insects and diseases. California utility PG&E has cut down more than half a million trees suffering from bark beetle infestation and drought. The cost of that, plus the risk that downed trees will cause fires, has changed the calculus. This summer, PG&E said it will spend $15 billion to bury 10,000 miles of new power lines. Daniel Tait of the Energy and Policy Institute says it's important to remember the wider context. Sixty percent of U.S. electricity still comes from fossil fuels, whose emissions heat up the planet.
DANIEL TAIT: Utilities are culpable in fueling climate change. And now we're looking at it. And utilities are having to adapt the very way that they do business down to vegetation management because of climate change.
SIMON: Even though more trees are dying from climate stresses, Igor Lacan in Oakland says the solution is not fewer trees. It's different ones.
LACAN: Planting a tree, they say, is a 50-year decision. And that's true.
SIMON: So, he says, we need to plant more trees that can thrive in hotter temperatures.
For NPR News, I'm Julia Simon in Oakland.
(SOUNDBITE OF MICROPHONES SONG, "I WANT WIND TO BLOW") Transcript provided by NPR, Copyright NPR.