When the international negotiations take center stage in Paris this December in the hopes of reaching an agreement to rein in climate change beginning in 2020, negotiators will be able to draw on the lessons learned in the voluntary carbon markets, according to a new report from Forest Trends’ Ecosystem Marketplace. Companies, governments, and individuals voluntarily spent just under $4.5 billion to purchase nearly one billion carbon offsets from projects that halt deforestation, install renewable energy, promote energy efficiency, distribute cleaner-burning cookstoves and more, according to Ecosystem Marketplace’s Ahead of the Curve: State of the Voluntary Carbon Markets 2015 report.