September 2016 was a milestone for the earth’s climate. It was the hottest September on record, nearly a degree Celsius warmer than the average from 1951 to 1980. It also was the first September where the Mauna Loa Observatory — “the gold standard for carbon dioxide monitoring” — measured the monthly average of carbon dioxide at more than 400 parts per million (ppm). Because September is almost always the annual low point for CO2 readings, that means the world has permanently crossed the 400 ppm threshold.

That also means what today we call the hottest September ever will soon be a normal, or even cool, September. Scientists have long forecast that if we could cut emissions enough to limit warming to two degrees Celsius, we could avoid the effects of climate change — including sea rise, crop failure, increased extreme weather — spinning out of control. We’ve already crossed the one-degree threshold and are projected to reach around four degrees. That’s about seven degrees Fahrenheit — imagine how different your state’s weather would be if temperatures averaged seven degrees warmer every day.

Is there any hope for the future? President Obama has made progress in cutting emissions and moving the country to cleaner energy. Facing a fanatically anti-environment GOP Congress, however, he has had to depend largely on executive branch powers. The next president will need to not only preserve those policies — among them limits on power-plant emissions, raised fuel standards and measures to reduce methane emissions — but also expand them.

Only one of the two presidential candidates has a climate policy; luckily, it’s the one holding a commanding lead. Hillary Clinton’s plan isn’t perfect: Her softness on the dangers of fracking and her embrace of the ethanol-boosting Renewable Fuel Standard program — which has done more to help the corn industry than the environment — are troubling. But she would also build on the president’s strengthening of fuel-economy and efficiency standards, include green energy projects in her national infrastructure plan, implement the landmark Paris climate deal and Obama’s Clean Power Plan and spend $60 billion to fund states and cities that want to go beyond White House goals for lower emissions.

If climate change is, in Clinton’s words, “a defining challenge of our time,” it’s disappointing to offer a strategy that can be summed up as “the status quo, but a little more so.” But as long as the Republican Party controls even half of Congress, executive actions will be the only weapons in the armory to fight climate change. More expansive ideas such as a carbon tax will never make it to the president’s desk. Progressively stronger executive actions may be enough, but nobody’s sure — and when the alternative is catastrophe, you’d like to be sure.

During the first Clinton-Trump presidential debate on Sept. 26, Hillary Clinton accused Trump of believing that "climate change is a hoax perpetrated by the Chinese," and Trump interrupted to object. (The Washington Post)

Democrats face steep odds in retaking both houses of Congress; under a Clinton presidency then, environmentalists likely would get more results if they focused on changing the climate debate rather than retaking Capitol Hill. Poll numbers offer some reason for optimism. Gallup reported in March that 64 percent of Americans worry about global warming, the highest percentage in eight years, and a record 65 percent now believe global warming is caused by “human activities.” The public is as receptive as it has been in nearly a decade. But work remains: Only 41 percent believe climate change is a serious threat, and another recent Gallup poll found that independents are split over whether 2015’s record temperatures were the result of “human-caused climate change” or “natural changes.”

Shifting the discussion is one area where, surprisingly, the 2016 campaign could change the climate debate for the better, even though climate change has been absent from the discussion. The contest has altered political journalism in a important way: As CNN’s Dylan Byers writes, “The traditional model of ‘he said, she said’ journalism . . . was thrown out the window in favor of a more aggressive journalism that sought to prioritize accuracy over balance.” More journalists have seen that the sky won’t fall if they treat falsehoods as falsehoods, and climate change is an obvious area to apply this new model. Senators should not be able to bring snowballs onto the Senate floor to “disprove” climate change without every headline fact-checking them. The realities of climate change are as much objective truth as the murder or unemployment rates. Regarding them as such will be an early test of whether political journalism has rededicated itself to the facts.

The debate over climate change is changing, but not as rapidly as it can or should. We have largely squandered decades that could have been spent heading off the danger, and now the consequences are no longer abstract. Climate change is a perilous threat to the country and the world; we must finally treat it that way.