People gather to protest President Trump’s announcement that the United States will pull out of the Paris climate agreement on June 1, 2017, in Washington. (Salwan Georges/The Washington Post)

ONE BYPRODUCT of the day-to-day chaos of the Trump presidency is that the nation's biggest, long-term challenges are often forgotten. While Washington spent last this week agonizing over the prospect of a totally unnecessary government shutdown, what should have been far bigger news went nearly unremarked.

According to NASA and the National Oceanic and Atmospheric Administration, last year was one of the warmest years on record — second or third, depending on which agency's records you examine, because each has its own method for its calculations. One reason it may not have topped 2016, the warmest year ever, was the presence then of a warming El Niño, a regular phenomenon the lack of which does not indicate that the planet is coping with radical, human-induced changes in the atmosphere's chemistry.

One warm year is not necessarily cause for concern. The trend, however, is. The past three years were the warmest three ever recorded. The five warmest years in the record all came since 2010. Seventeen of the 18 warmest years in the data came since 2001. This decade is on track to be warmer than the 2000s, which were warmer than the 1990s, and so on. The heating of the Earth is unmistakable.

Some climate doubters insist that while the warming trend is established, humans' responsibility is not. This assertion is nearly as absurd as denying the warming in the first place. It is not coincidence that breakneck warming occurred just as humans began pumping increasing amounts of heat-trapping gases into the atmosphere. Scientists have spent more time than necessary examining other offered causes — such as solar activity — only to conclude that those supposed causes cannot account for the patterns of warming clear in the data.

Others argue that the country should not get lost in an unsolvable disagreement on the science but rather just talk about solutions. But without a clear sense of the problem, policymakers will waste time and money on the wrong responses. If global warming were a totally natural phenomenon, the task would be simply to build a society more resilient to temperature extremes, crazy weather, droughts, floods and scrambled-up ecosystems. But because humans are warming the planet, the top priority must be to remove the underlying cause by cutting greenhouse gas emissions.

Last year also marked a recent low in the federal government's response to climate change. President Trump installed a climate-change denier, Scott Pruitt, at the Environmental Protection Agency, signaling the end of landmark climate rules on power companies. Mr. Trump's energy secretary, Rick Perry, pushed for a pro-coal policy so absurd that the independent Federal Energy Regulatory Commission rejected it out of hand. The president also announced he would pull out of the Paris climate agreement, an accord that the United States spend years fine-tuning to ensure it was a fair deal.

In 50 years, many of the unnecessary distractions that Mr. Trump packed into his presidency will be forgotten. But no one will forget how selfishness and purposeful ignorance reigned in the United States as the world began to cook.