The 18th Annual Chatham House Conference on Climate Change being held today in London is, for better or worse, sponsored by Shell. As one of the world’s leading oil and gas companies, Shell hasn’t exactly been a friend to the environment, though the company would point out that it encourages sustainable designs like this football field powered by human energy in Brazil. Environmentalist Bill McKibben, the conference’s keynote speaker, used his time at the podium to ream out the event’s unlikely corporate sponsors:

I didn’t know Shell was sponsoring this conference when I agreed to do it, but I’m glad for the chance to say in public that Shell is among the most irresponsible companies on earth. When they write the history of our time, the fact that Shell executives watched the Arctic melt and then led the rush to go drill for oil in that thawing north will provide the iconic example of the shortsighted greed that marks the richest people on our planet.

Well then. Since the conference is being held at the Chatham House, its attendees must follow the renowned Chatham House Rule: The identity of speakers isn’t disclosed to the public in order to encourage open and free debate. Despite the rules, however, McKibben’s speech quickly became a matter of public record when his own organization 350.org posted it and conference attendees tweeted highlights.

Unswayed by the promise of anonymity, fossil fuel reps declined to counter McKibben’s takedown, apparently.

Environmentalists were clued into the discord before the conference had even started: In the lead-up to the event, Shell displayed ads and billboards around London touting its commitment to climate action. Protesters outside the conference echoed McKibben’s sentiments about Shell’s sponsorship.

A spokeswoman from Shell declined to comment directly on what McKibben said, but referred Quartz to a speech on energy policy that Shell CEO Ben van Beurden gave at Columbia University in September.