ExxonMobil, a titan of corporate America, faces a pivotal moment this week as restive shareholders have their say on what critics call an inadequate response to seismic shifts brought on by climate change. On Wednesday, the most watched proxy battle in years will end in a vote to decide who sits on ExxonMobil’s board. The company is trying to fend off a challenge from upstart hedge fund Engine No.l, and after a string of recent endorsements the activists think victory is within grasp.

“This will reverberate,” said Anne Simpson, head of board governance and sustainability at Calpers, a US pension fund backing the activists. “Winds of change are blowing through companies that are reluctant, fearful or unsure about how to take action [on climate].” The battle has been under way since December, when Engine No.l nominated four new directors for Exxon’s board and called for “purposefully repositioning the company to succeed in a decarbonising world”.

Exxon, once notoriously aloof to shareholders, has been in listen-and-respond mode since the activist threat emerged, already appointing fresh directors and unveiling new emissions plans. Darren Woods, the chief executive, told the Financial Times that he was ready to lead the board shareholders elected. “We will work with whatever comes out of the annual meeting,” he said.

The vote will cap a contentious proxy season in which Shell, Conoco, BP and other fossil fuel producers have faced investor criticism over their climate strategies. Chevron’s board also faces emissions-related shareholder resolutions at its annual meeting, starting just after Exxon’s on Wednesday.

Calpers, Calstrs, and the New York state retirement fund, the US’s three biggest pension funds, will all back Engine No.l’s proposals, as will Legal & General Investment Management and the Church Commissioners for England.

By contrast, Norway’s huge sovereign wealth fund, which has talked extensively of companies’ climate risk, said it would withhold its vote for Woods but back the rest of the management’s board slate.

The vote will hinge on BlackRock, Vanguard, and State Street — the big three funds together hold more than 20 per cent of Exxon’s stock — and the supermajor’s huge retail investor base, accounting for almost half of its