Endorse a market-based climate solution
Specific ask: Endorse the House and Senate versions of the Energy Innovation and Carbon Dividend Act. They can do so here: energyinnovationact.org
Background, in a nutshell:
The above graphic shows the incredible potential of free energy delivered to us safely and uniformly over the planet.
Renewable on the left, at an annual rate.
Non-renewables on the right--total, for ever.
Energy budgets are shown by relative size. The big yellow circle represents an annual supply of solar energy from the sun: about 14,000 times more than we now use.
All we need is the infrastructure to harness it.
A smart grid, storage, energy efficiency technologies, and that is just the beginning of the clean energy economy. Jobs, national security, less pollution. We have the technology. We lack the policy and predictable market horizon. Otherwise this would have happened 20 years ago.
We will make this transition eventually. The only question is will it be in time.
As a leading voice in the investing and business community, Vanguard can help.
Climate change is detrimental to global economic prosperity. According to Citigroup, GDP lost to climate change may reach $44 T by 2060.  Poorer air quality will harm public health, extreme weather will damage infrastructure, and heat stress will decrease agricultural production. 
Since Vanguard owns stock in all parts of the economy, the long-term success of the world economy is crucial to Vanguard's financial performance. This means that Vanguard has an enormous stake in preventing climate change.
Economists and the Intergovernmental Panel on Climate Change agree that pricing carbon is a concrete and cost-effective way to slow climate change.  Bipartisan carbon pricing legislation is becoming concrete: The Energy Innovation and Carbon Dividend Act of 2018  has been introduced into the House of Representatives, and will help bring climate change under control by enacting a carbon fee and dividend into law. Many of the companies you invest in have already expressed support for the bill, including Gap Inc., General Motors, Schneider Electric, IKEA, and Unilever.
When explaining Vanguard's lack of leadership on climate change, Vanguard's Investment Stewardship Officer said that it "does not hear from many of its 20 million investors on governance."  It is time for us, Vanguard's investors, to let it know that we want it to reduce the risk of its portfolio by supporting climate action.
I ask Vanguard to endorse the Carbon Pricing Principles  to help move the US towards cost-effective climate solutions. The Carbon Pricing Principles endorse policy that:
Enables the US to achieve its 2025 greenhouse gas reduction goals and puts US emissions on the path keep global temperature increases well below 2 degrees Celsius.Establishes an economy-wide system to price carbon emissions.Increases the global competitiveness of US businesses.Provides a price signal strong enough to reduce the need for future regulation of carbon emissions, while preserving the EPA's present Clean Air Act regulatory authority.Provides flexibility to use complementary policies to reinforce effect of carbon pricing.Preserves all families’ access to reliable, affordable energy.Ensures a just transition for affected workers, families, and communities.Incentivizes comparable action by other nations. https://ir.citi.com/hsq32Jl1m4aIzicMqH8sBkPnbsqfnwy4Jgb1J2kIPYWIw5eM8yD3FY9VbGpK%2Baax
I and my wife hold about $1M of Vanguard index funds.
And I suspect Jack Bogle would be proud of them if they do this.