Thousands of workers from Amazon, Twitter, Google, Microsoft, Facebook, Square, and other tech companies are expected to walk out today as part of a worldwide climate change strike led by 16-year-old activist Greta Thunberg. After Amazon workers announced they were joining the demonstration last week, employees from other Silicon Valley firms began joining in. The same group of Amazon employees have been pushing the company to reduce its carbon footprint for nearly a year. Now, over 1,700 of them and counting have said they will join Friday’s walkout, which is expected to draw millions of participants in cities around the world.

The tech workers participating in the strike are part of a wider wave of employee activism that has spread across Silicon Valley over the past year. Many of those demonstrations concerned workplace issues at individual companies, such as sexual harassment or controversial government contracts. Friday's walkout represents a broader coalition across different corporations, focused on an issue facing the entire planet. Many of these employees make up one of the most privileged and highly visible labor forces in the world, working for innovative and resource-rich companies. If their efforts on climate change keep gaining momentum, they may have a significant impact, especially as the Trump administration continues to roll back environmental initiatives.

"I think as a business we are supposed to be customer obsessed, and as employees we are supposed to challenge leadership on what we think is best," says Kevin Imrie, a recruiter at Amazon's office in Toronto, where he says dozens of people participated in the strike earlier today. "I’m a shareholder, and a good employee, and this is the right thing for us and our customers."

Ahead of today’s demonstration, both Amazon and Google leadership announced new environmental initiatives. At an event in Washington, DC, on Thursday, Amazon CEO Jeff Bezos unveiled a new “Climate Pledge,” which entails meeting the goals of the Paris climate agreement 10 years early and becoming carbon neutral by 2040. Bezos promised Amazon would order 100,000 electric trucks from Rivian, a startup it invested hundreds of millions of dollars in earlier this year, and have them all on the road by 2030. Also on Thursday, Google CEO Sundar Pichai announced what he called “the biggest corporate purchase of renewable energy in history,” which includes 18 new energy deals.

The Amazon group organizing today’s walkout, Amazon Employees for Climate Justice, said in a statement Thursday that their employer’s new sustainability initiatives are a “huge win,” but ultimately don’t go far enough. Amazon has not dropped its contracts with oil and gas companies for optimizing the discovery and extraction of fossil fuels, and continues to donate to climate-denying politicians and think tanks. Bezos didn’t commit to either of his employees’ asks, and said Amazon would continue working with energy companies. Employees at other tech firms, like Microsoft and Google, have adopted the same demands for their employers.

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Bezos also didn’t address the massive size of Amazon’s carbon footprint, which was revealed for the first time Thursday on a new Amazon sustainability website. There was no mention of the figure in Amazon’s press release announcing the Climate Pledge, but at 44.4 million metric tons, it puts the company in the top 150 to 200 emitters in the world, according to an expert who spoke with The New York Times. The statistic takes into account manufacturing of Amazon devices like Kindles and Echo speakers, gas consumed by delivery trucks and planes, electricity used by its cloud-computing data centers, business travel, packaging, and other purchased goods and services.

Amazon Employees for Climate Justice is pushing for the company to be more forthcoming about how it calculates its impact on the environment, in case it may be underselling its total carbon footprint. “We must also consider: which parts of our supply chain aren’t included when Amazon reports our emissions?” they asked in their statement. “We look forward to working with leadership to understand these questions, and to working to ensure transparency and accountability.”