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Bill Gates today pledged his support for a Washington initiative that could make the state the first in the nation to put a price on carbon emissions in the hopes of slowing climate change.

The Microsoft co-founder and second-richest person on the planet urged others to join him in voting for Initiative 1631 on November’s ballot. While he admitted to initial skepticism, he wrote in a post shared on LinkedIn: “It’s important to remember what is at stake. Climate change may be the toughest problem humanity has ever faced. To avoid the worst scenarios, we need to reduce global net greenhouse gas emissions to essentially zero in the next 50 years.

“Changing how we power our homes and cars won’t be enough,” Gates wrote. “We also need to get to zero in every other major source of greenhouse gases, including manufacturing, transportation, and agriculture.”

On Monday, top scientists warned that the world will experience dire effects from climate change sooner than expected unless we quickly embrace significant cuts to greenhouse gas emissions. The report by the Intergovernmental Panel on Climate Change said that the planet must dramatically curb the release of carbon dioxide and other pollutants over the next dozen years to cap warming at 1.5 C, otherwise risk serious flooding, droughts, and heat waves. They predicted worsening wildfires, food shortages and massive die-offs of coral reefs.

The Washington ballot measure puts a $15 per ton fee on carbon emissions to be paid by the oil industry and power companies using fossil fuels. The money will go toward clean energy investments including renewable power, public transportation, and energy efficiency upgrades for buildings. A portion of the fee is directed toward low-income residents that could be affected by higher fuel prices.

Others in the Northwest tech sector have pledged support for the measure as well. Craig McKibben, co-founder of the software company WRQ, and his wife, Sarah Merner, have given $1 million to the initiative, based on filings with Washington’s Public Disclosure Commission (PDC). Other tops donors include Chris Stolte, co-founder and technical advisor for Tableau, and Nick Hanauer, a venture capitalist and early Amazon investor. Each has given $250,000.

Tomorrow, Seattle-based startup EnergySavvy, a company working with utilities trying to increase energy conservation, is hosting a public event in support of I-1631. Washington-based businesses including Expedia and REI have joined the “yes” camp as well.

In his post, Gates gave three reasons for his decision to support the initiative. He wrote that the measure will help make Washington a hub for clean energy innovation with the potential for job creation, sends a clear market signal to encourage more widespread the adoption of renewable energy available today, and helps keep the state’s nuclear power and hydropower sectors competitive with other energy sources.

“Can innovators in our state solve this global problem on their own? Of course not,” Gates wrote. “But at a time when Congress isn’t focusing on this issue, states can develop their own ideas and explore what works now. This is an opportunity for Washington to lead the way.”

At a time when Congress isn’t focusing on this issue, states can develop their own ideas and explore what works now. This is an opportunity for Washington to lead the way.

Gates also supports Breakthrough Energy Ventures, a $1 billion private fund to help entrepreneurs launch clean energy companies.

Gates said that he would be contributing to the I-1631 campaign, but did not say how much. At this point, those in favor of the carbon fee lag well behind the opposition, which is backed by the oil industry. Committees supporting the measure have raised more than $8.4 million, while the opposition has more than $21.3 million.

Former New York City Mayor Michael Bloomberg announced last week that he would give $1 million in support of I-1631. Other donors include The Nature Conservancy, with $1 million in contributions, and the League of Conservation Voters with $900,000. The committee backing the initiative is Clean Air Clean Energy WA. In addition to environmental groups, labor organizations and groups representing racial minorities are also supporting the measure.

Committees fighting I-1631 include No on 1631 sponsored by the Western States Petroleum Association and an effort backed by the Association of Washington Business. Top donors are fuel refineries and include Phillips 66, BP, Andeavor, American Fuel and Petrochemical Manufacturers, and U.S. Oil and Refining Company.

An opinion piece in the Seattle Times challenging the measure called it an “unfair energy tax that would force Washington families, small businesses and consumers to pay billions more in taxes for gasoline, home heating costs, electricity, natural gas and pretty much anything else that requires energy to be manufactured or shipped here in Washington.”

The election is Nov. 6 and ballots will be mailed out to registered voters on Oct. 19.