Two, if they're public servants with a gift for mobilising countries from China to the USA.
The headline-grabbing agreement at the Paris climate conference in December overshadowed another significant international climate deal concluded in the same week. After a whirlwind of last-minute phone calls, Swedish Energy Minister Ibraham Baylan took the stage to announce the Global Lighting Challenge: a commitment by 14 countries, including the USA, India and China, and huge manufacturers like Philips and Osram to ensure the sale of 10 billion energy-efficient LED bulbs in the next few years. The potential reduction in carbon emissions is enormous. With current technology it would be possible to provide 50% more lighting around the world at half the carbon cost. At the time of writing, more than 50 million bulbs have already been sold.
See the rest of the World Economic Forum article here.