The Fourth National Climate Assessment, released Friday by the U.S. government, puts it starkly: “Observations collected around the world provide significant, clear, and compelling evidence that global average temperature is much higher, and is rising more rapidly, than anything modern civilization has experienced, with widespread and growing impacts.” The report notes that “annual average temperatures have increased by 1.8°F across the contiguous United States since the beginning of the 20th century” and that “annual median sea level along the U.S. coast . . . has increased by about 9 inches since the early 20th century as oceans have warmed and land ice has melted.”

The report attributes these changes to man-made greenhouse gases and warns: “High temperature extremes, heavy precipitation events, high tide flooding events along the U.S. coastline, ocean acidification and warming, and forest fires in the western United States and Alaska are all projected to continue to increase, while land and sea ice cover, snowpack, and surface soil moisture are expected to continue to decline in the coming decades.”

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The U.S. government warnings echo the United Nations’ Intergovernmental Panel on Climate Change. In October, it released a report that represented the work of 91 scientists from 60 countries. It describes, in the words of the New York Times, “a world of worsening food shortages and wildfires, and a mass die-off of coral reefs as soon as 2040.”

The wildfires are already here. The Camp Fire blaze this month is the most destructive in California history, charring 153,000 acres, destroying nearly 19,000 structures, and killing at least 85 people. The second-most destructive fire in California history was the one last year in Napa and Sonoma counties. The Yale School of Forestry and Environmental Studies notes that climate change has contributed to these conflagrations by shortening the rainy season, drying out vegetation and whipping up Santa Ana winds. Massive hurricanes are increasing along with wildfires — and they too are influenced by climate change.

It’s time to sound the planetary alarm. This is likely to be the fourth-hottest year on record. The record-holder is 2016, followed by 2015 and 2017. A climate change website notes that “the five warmest years in the global record have all come in the 2010s” and “the 10 warmest years on record have all come since 1998.”

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Imagine if these figures reflected a rise in terrorism — or illegal immigration. Republicans would be freaking out. Yet they are oddly blasé about this climate code red. President Trump, whose minions buried the climate-change report on the day after Thanksgiving, told Axios: “Is there climate change? Yeah. Will it go back like this, I mean will it change back? Probably.” And, amid a recent cold snap, he tweeted: “Brutal and Extended Cold Blast could shatter ALL RECORDS - Whatever happened to Global Warming?”

By this point, no one should be surprised that the president can’t tell the difference between short-term weather fluctuations and long-term climate trends. At least he didn’t repeat his crazy suggestion that climate change is a Chinese hoax. Yet his denialism is echoed by other Republicans who should know better. Sen. Joni Ernst (R-Iowa) told CNN on Sunday: “Our climate always changes and we see those ebb and flows through time. . . . We need to always consider the impact to American industry and jobs.”

We do need to consider the impact on U.S. jobs — but that’s an argument for action rather than, as Ernst suggests, inaction. The National Climate Assessment warns that global warming could cause a 10 percent decline in gross domestic product and that the “potential for losses in some sectors could reach hundreds of billions of dollars per year by the end of this century.” Iowa and other farm states will be particularly hard hit as crops wilt and livestock die.

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Compared with the crushing costs of climate change, the action needed to curb greenhouse-gas emissions is modest and manageable — if we act now. Jerry Taylor, president of the libertarian Niskanen Center, estimates that a carbon tax would increase average electricity rates from 17 cents to 18 cents per kilowatt-hour. The average household, he writes, would see spending on energy rise “only about $35 per month.” That’s not nothing — but it’s better than allowing climate change to continue unabated.

I’ve owned up to the danger. Why haven’t other conservatives? They are captives, first and foremost, of the fossil fuel industry, which outspent green groups 10 to 1 in lobbying on climate change from 2000 to 2016. But they are also captives of their own rigid ideology. It is a tragedy for the entire planet that the United States’ governing party is impervious to science and reason.