ANY GOOD business executive knows that the world is full of risks, ignored at a company’s peril. Interest rates could spike. China could change its currency policy. Chaos in Iraq could push up gasoline prices. Smart firms account for these possibilities as best they can, adjusting business plans so that they aren’t caught flat-footed. The same can be said of wise societies.

In late June , a bipartisan group of economic leaders argued that the United States must take this approach when facing the risks of climate change. It’s still not perfectly clear how sensitive the climate will be to a given increase in atmospheric greenhouse-gas emissions. Nor is it perfectly clear how ongoing temperature change will affect complicated Earth systems. But these are not excuses for doing nothing, or too little, to reduce carbon dioxide emissions.

To back up its claims, the group — led by, among others, Hank Paulson and Bob Rubin, treasury secretaries for George W. Bush and Bill Clinton, respectively — commissioned an analysis of the risks that climate change poses to the United States. They only attempted to quantify the impact of a few changes that scientists are confident will occur to some degree with unabated warming: sea-level rise, higher storm surges, heat extremes, higher demand for energy and changes in agricultural production. As with a climate assessment the Obama administration published this year, the results should — but probably won’t — snap Congress into action.

Scientists already are observing climate changes in the United States. They will grow worse. Higher seas mean higher storm surges and more at-risk property along heavily populated coasts — $66 billion to $106 billion worth will likely be below sea level by mid-century. The annual national storm cleanup tab will balloon. As the country warms, the average American will likely see a month’s worth — or more — of days over 95 degrees. The South and Southwest will be much hotter than that. The analysis considered how many cold-related deaths further warming would prevent and concluded that heat-related deaths would outweigh the potential benefit. Similarly, farmers in northern latitudes might see longer growing seasons, but those farther south, in what has been prime farming country, will have to make costly adjustments, changing what they grow and developing crops that can adapt to climate extremes. In the long term, uncontrolled warming could even produce days in the United States in which humans literally could not survive long without air conditioning.

“Hope is not a strategy,” Mr. Paulson said to us. But that is the strategy that Congress, in its perpetual inaction, is taking: Hoping that the scientists are dramatically wrong — or at least that the country can deal with the problem later. If Congress were the board of a large company, ignoring such a serious risk would give shareholders ample reason to fire every head-in-the-sand director. Voters might want to contemplate the analogy this November.