Mitigating climate change is not just a good idea, it’s the law—at least it is in the Netherlands, and other countries may soon follow suit. In a landmark ruling last month, a court in The Hague ordered the Dutch government to cut its greenhouse gas emissions by at least 25% within five years in the first climate liability suit brought under human rights and tort law. The court found the government’s current pledge—a 14% to 17% reduction—unlawful given the threat of climate change and asserted that the government had an independent legal obligation to its citizens apart from any international pacts. The ruling is poised to create a ripple effect, inspiring activists in other countries; indeed, there is already a nearly identical case in Belgium. Even more importantly, this victory can offer key momentum in the lead-up to the climate negotiations in Paris this December. It shows governments around the world that activists have a new tool to hold them accountable to their promises—and to make those promises even bolder.