The last time I saw Rebecca Tarbotton, one of the few women leaders of a major US environmental organisation, deliver a speech was on a cold San Francisco night in October in the African Hall of the California Academy of Sciences.

The executive director of the Rainforest Action Network (RAN) since 2010, Becky, as she was known, held the roomful of friends, donors, and colleagues enraptured as she shared her vision for RAN and announced how she and her staff had helped the giant Disney corporation create the most environmentally sound paper purchasing policy in the industry. I just watched the speech again – you can view it here – and seeing her so vibrant, it's still hard to believe that Becky died on 26 December, 2012 after being overcome by rough waves while on vacation in Mexico. She was 39.

As a board member of the Rainforest Action Network and a friend, I was devastated. But this is more than just a personal loss. Becky's death is a loss for all of us. The speed at which we're destroying rainforests and heating the planet is a reminder of the urgency to address the fundamental crises of our time: forest destruction and climate change. And we have no surplus of graceful, visionary, strategic leaders.

The first woman to lead RAN in its 25-year history, Becky was a brilliant campaigner and a deep thinker. She was, as her friend and co-conspirator Bill McKibben said, "a hero among heroes".

Before becoming RAN's executive director, Becky served as the organisation's finance campaign director, tackling one of the biggest sources of greenhouse gas emissions: coal.

"She spent much of her time focused on the science of change-making," explained Nell Greenberg, who worked hand-in-hand with Becky as the organisation's communications director. "Becky wanted to create campaigns that achieve what she called 'transformational change' – change that fundamentally addresses environmental destruction and human rights abuses."

Out of this thinking came a strategy to take on the institutions financing fossil fuel projects. With partners around the country, Becky created the first ever sector-wide bank policy, known as the Carbon Principles, to limit the financing of fossil fuel projects and coal plants. Using a combination of direct action, negotiation, and consumer pressure – a trademark RAN trifecta – Becky helped push the country's top eight banks, including Bank of America and Wells Fargo, to limit their financing of companies that practice mountain top removal coal mining.

In 2010, Becky became acting director at RAN when Mike Brune left to take over at the Sierra Club. Under Becky's leadership, RAN continued to work towards transformational change by drawing the connections between forests and climate ever more clearly. "She believed that to protect forests and our communities we must protect our climate, and to protect our climate we must protect the forests," said Greenberg.

During her talk at the Academy of Sciences Becky announced, to thunderous applause, perhaps her biggest achievement: the Disney corporation had worked with RAN to develop the most far-reaching paper procurement policy in the industry, agreeing to no longer source its paper from rainforests or conflict zones.

The success was a classic example of Becky, and RAN, at work: 18 months earlier, RAN had lab tested children's books and discovered that 60% were made from fibres that could be traced back to Indonesia's rainforests. Deforestation there had made that country one of the world's leading greenhouse gas emitters and was devastating the last remaining habitat for the endangered orangutan.

Armed with the facts, RAN called on the world's biggest publishers to change their paper buying practices. Most did, but not Disney – the world's largest publisher – at least not at first.

Frustrated by Disney's dismissal of these concerns, RAN organised a direct action on the company's doorstep. They dropped a banner over the executive headquarters that said: "Disney: Destroying Indonesia's Rainforests" while a cute Mickey and Minnie Mouse chained themselves to the gates, chainsaws in hand. The police making the Mickey and Minnie arrests, Becky said, were doubled up in laughter. The local media loved it; the story blanketed Los Angeles.

Within a week, six executives were at RAN's office, talking about what it would take to develop a policy that would truly protect forests. Disney wanted a policy that would apply not just to their children's books, but to all 1,700 subsidiaries and all paper products, from the napkins on cruise ships to the cardboard inserts in toys.

Many months later that's just what they did. On 11 October 2012, Becky announced the Disney policy, calling it "one of the most far-reaching paper policies ever - one that included groundbreaking safeguards for the climate and human rights […] What excites me most about Disney's commitment," Becky said, "is its depth, affirming that the company will avoid not only tropical deforestation, but also go above and beyond to protect human rights and to recognise the high carbon value of rainforests – two things rarely seen in policies of this kind."

Becky was a natural leader: in her orbit, you were stirred to shine brighter, work harder, think more strategically. In her presence, you felt instantly motivated, inspired, activated.

But she also actively cultivated her leadership skills, reflecting as much on what it takes to be a great leader as what it took her to be a great campaigner.

Under her tenure, Becky constantly sought out fresh ideas and alternative perspectives. She had an open door policy and would always welcome new ideas in all her interactions, whether with the CEO of a bank or one of her staff. "She wasn't dogmatic about problems – or solutions," said Greenberg.

In 1972, Yale psychologist Irving Janis coined the term "Groupthink" to explain how really smart people can collectively make really dumb decisions. Janis found Groupthink happens when leaders create organisational cultures where conflict or dissent is feared, where alternative ideas or viewpoints are not welcomed. Janis didn't have a term for the opposite of Groupthink, but through her leadership style that's exactly what Becky fostered.

I also loved what she proved about the essence of power; she showed power is not zero-sum, she was powerful without being power hungry. She knew that sharing power, and with it sharing ownership of success, creates stronger organisations and more effective campaigns. When she announced the Disney campaign achievements that night at the Academy of Sciences she called on the forest campaigners to stand. Amidst the loud applause Becky publicly thanked these four people for helping transform the purchasing decisions of a $40bn company.

As she closed the evening that night, Becky said: "We don't always know exactly what it is that creates social change. It takes everything from science all the way to faith, and it's that fertile place right in the middle where really exceptional campaigning happens – and that is where I strive to be."

It's more than difficult to begin 2013 without Becky, but it is made a little less painful knowing that so many people around the world were inspired by her vision and are committed to carrying it on.

Anna Lappé is a board member of the Rainforest Action Network and the author most recently of Diet for a Hot Planet: The Climate Crisis at the End of Your Fork and What You Can Do About It and the co-founder of the Small Planet Institute.

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