Best path to international environmental career?

Hello everyone! I’m currently a high school senior planning to attend college and major in some sort of engineering, at the moment I’ve been thinking Materials. I want to pursue a career in an environmental field (renewable energy, water resource conservation, env policy) and lately I’ve also been thinking I would love to work for a UN/international agency like UNEP or the IPCC. Does anybody know any tips toward achieving this end? Would any of these organizations even want someone with an engineering background? Any advice is appreciated, thanks!