Exxon Mobil is wielding its public relations might against the fossil-fuel divestment movement, signaling that climate-change activists have struck a nerve at the world's biggest publicly traded oil and gas company. Exxon Mobil's blog, titled "Perspectives," posted a lengthy attack Friday about the divestment movement, which urges universities, churches, pension funds, and other big institutional investors to dump their shares of oil and coal companies as part of the fight against global warming.