It is impossible to overstate how important this is. On Tuesday, President Obama will lay out a plan for dealing with climate change, and reports indicate it will include regulation of carbon emissions from existing power plants. If those reports are correct, and those Executive Branch regulations take effect after certain ferocious legal opposition by every vested interest hurt by pricing carbon emissions, this could be the single most important step in mitigating anthropogenic climate change the world has ever seen.

     The White House released this video to announce the coming address. Julie Eilperin, former environment beat reporter and now White House correspondent for the Washington Post, reports that the plan will include regulations on greenhouse gas emissions from existing power plants, not just limits that plants built in the future must meet. Adam Restuccia at Politico had an even richer piece suggesting what the plan will include.

     Coal-fired plants emit huge amounts of CO2. They are the obvious first targets. But so do natural gas plants; half as much as coal, but still massively more than nuclear, and renewables. The energy economy in the United States has been turning toward natural gas-powered electricity for the last few years, ever since new recovery technologies like fracking opened massive new supplies and dropped the price of natural gas. It remains to be seen just how tight the Obama limits on greenhouse gas emissions will be, but if they are based on an overall national emissions reductions goal, which Obama has promised in the past, natural gas plants will certainly be impacted. If so, the cost of a kilowatt of natural gas-produced electricity will go up, making carbon-free sources of generation like nuclear and renewables, and energy conservation programs, more cost-competitive, and more attractive to investors and energy companies. What Obama announces on Tuesday, then, promises to dramatically reshape the economics of energy.

     This will also send a huge signal internationally, that the world’s largest economy and second largest CO2 emitter is finally seriously committed to reducing those emissions. Those reductions can’t happen without major changes in the energy economy in the United States. Investment and growth that strengthens the renewables and nuclear industries in the U.S. will have major impacts on the economics of those parts of the energy economy worldwide.

     There is something else in what the White House is planning that may be almost as pivotal, though not as sharply obvious. The plan will include steps to “prepare our country for the impacts of climate change…”  In other words, the debate about climate change IS OVER. It’s time to act to protect public and environmental health and safety, national security, the American agricultural economy, and ever other major sector threatened by the sorts of things that scientists say climate change may already be contributing to and almost certainly will be in the near future. It’s one thing for the mayor of New York to suggest that 'The debate is irrelevant…it’s time to invest in insurance against the risk, and to propose a $20 billion dollar investment to protect the city from future floods.  It is far more profound to hear this from the White House.

    This subtle but important shift essentially says to the ideologues and vested economic interests who continue to promote doubt about climate change in the face of overwhelming evidence from one of the largest research projects in human history; The debate is over. Climate change is real, human activity is a cause, and serious impacts are already happening or likely to happen because of the emissions already in the atmosphere. The White House plan to prepare for the impacts of climate change is a clear statement that at the highest level of government in the United States, the debate is now just political noise. It is time to act. That commitment has long since been made by many countries, states and cities, of course, but it will carry huge significance coming from the federal executive branch.

     As polarized as the political right has made this issue - polarization that began in the early 90’s with campaigns by conservative groups and oil and coal interests to sow doubt -  the political debate will certainly continue, and the media, attracted to such noise as mindlessly as fish are to bright shiny objects in the water, will keep that debate alive. But the White House is saying that as far as policy making to protect the public and the national interest is concerned, it’s over. The time for action has come.

     We will have to wait, of course, to see just what is announced, and longer to see how the proposals play out, against fierce opposition and legal action. But given how serious the impacts of climate change are likely to be, it is hard to overstate the importance of what the President will apparently announce. It may truly be a signal day in the fight over one of the biggest threats humans have ever faced.