This month, an unexpectedly high 49% of shareholders backed a resolution urging Occidental Petroleum, another American oil firm, to stress-test a two-degree scenario. Some 42% voted for climate-related resolutions at Anadarko, a rival, and AES, a utility. Robert McCormick of Glass Lewis, a proxy advisory firm, says such a large vote suggests that usually placid asset managers, such as mutual funds, may have joined the green revolt alongside pension funds—more established rebels. He notes that the resolutions, even if passed, would be non-binding. But if they are ignored, shareholders can express their frustration in subsequent years by refusing to support a company’s board nominees, he says.

The pressure on the American supermajors follows the “Aiming for A” campaign by institutional investors in Britain that last year forced Royal Dutch Shell and BP, the biggest European oil firms, to agree to reveal how stringent climate-change policies would affect their investment portfolios. Change across the Atlantic has proved harder to effect. Anne Simpson of CalPERS says shareholders have weaker rights in America, which has a more litigious corporate culture and where it is harder to challenge boards than in Britain. She talks of a “shut up or sell up” mentality.

Hence CalPERS is seeking “proxy access” at ExxonMobil that would give large shareholders the right to nominate board members. This is a growing trend in corporate America (a majority supported proxy access at Chevron last year), and Ms Simpson says it is aimed at installing a “climate-competent” board at ExxonMobil. The firm continues to reject it, even though last year the proposal gathered 49.4% of shareholder support. “If we can’t hold boards accountable we may as well sit and whistle,” she says, adding: “If we don’t win this year, we will be back next year.”

Yet even when firms agree to such resolutions, there is no guarantee their level of disclosure will satisfy investors. On May 11th Shell issued two reports on its assessment of climate-change risks in response to last year’s vote. Full of pretty pictures and snazzy charts, they revealed little about how climate policies would alter future plans for developing oil- and gasfields.