San Jose Mercury News: Federal researchers warned Thursday that warming temperatures could soon cause California’s beloved giant sequoia trees to die off more quickly, so forest managers must start considering the impacts of climate change and a longer, harsher wildfire season. Hot, dry weather over the last two decades already has helped to kill an unusual number of old-growth pine and fir trees growing in Yosemite and Sequoia national parks, according to recent research from the U.S. Geological …