But another kind of climate change is also at work. The global political climate is heating up, and the rising geopolitical temperature is likely to hit faster and could wreak more havoc than anything Greenpeace is worried about. Geopolitical climate denialism is a more urgent danger to national security than melting glaciers in Greenland.

President Barack Obama was the Great Denialist in geopolitics, temporizing and tap dancing, appeasing and apologizing as an axis of anti-American revisionist powers consisting of China, Russia, Iran and their satellites stepped up their resistance and began to coordinate policies. Russia invaded Ukraine and re-entered the Middle East, China embarked on the greatest military buildup in the history of the world, and Iran built up a regional empire while Washington dreamed beautiful dreams.

Team Biden came into office knowing that the geopolitical world was getting hotter, but believing that the root cause was Donald Trump’s bull-in-a-China-shop approach to foreign policy. Put the smart people back in charge, restore some nuance and diplomatic finesse to the system, repair the trans-Atlantic relationship, and all would be well. “Park” Russia by reaching an understanding with Vladimir Putin, park Iran by re-entering the nuclear deal, and then firmly but carefully clip China’s wings while inviting Beijing to cooperate on real issues of the day, like global governance and climate change.

It was an elegant, almost Obamian strategy, awash in subtlety and finesse. It had one flaw. It could work only if America’s adversaries went along.

They didn’t. Instead of rolling tamely into the parking lot, Russia invaded Ukraine and doubled down on its efforts to build a sphere of influence in Africa. Iran turned up its nose at Mr. Biden’s offer to relaunch the nuclear deal and intensified its drive toward regional hegemony and nuclear weapons. And China responded to American pressure by deepening its ties to Russia and Iran while stepping up the pressure on Taiwan.

This summer we’ve seen the geopolitical equivalent of a record heat wave. The war in Ukraine escalated as Russia stepped up its missile attacks and withdrew from the grain-shipping deal that limited the cost of the war to poor countries in the Middle East and beyond. Iran’s threats to Gulf oil shipping are so serious that the administration has been forced to plan for Marines to be deployed to protect oil tankers. Russia is deepening its economic ties with North Korea and engaging in joint naval maneuvers with China around both Japan and Alaska. And in the Sahel, the overthrow of the pro-Western president of Niger by an apparently pro-Russian junta has led the Biden administration to back moves by neighboring nations that could lead to armed conflict with American troops at risk.

President Biden’s basic problem is that our adversaries believe their strategy of turning up the heat is working. With the 2024 election approaching and isolationism rising in both political parties, adversaries around the globe hope that America’s commitment to the current world order will crack as it comes under growing strain.

To give credit where it is due, the administration has taken some smart steps as it gradually grasped the gravity of the situation. It walked back the foolish policy of alienating Saudi Arabia and began to rethink its posture in the Middle East. It embraced Indian Prime Minister Narendra Modi. It is engaging in the Sahel. It continues to support Ukraine even if moving too slowly on weapons like F-16s.

But there is one vital thing it is still failing to do. While the Biden administration has discovered that the world is a more dangerous place than it thought back in January 2021, too many Americans still think we are living in Barbie’s world, not Oppenheimer’s. Mr. Biden, backed by responsible leaders in both parties, needs to alert the country to the very real dangers we face around the world.

A united and vigilant America can still deter our adversaries from pressing their challenge to a point of no return. New wars that would dwarf the Ukraine conflict, engage Americans in direct combat, and potentially engulf the entire planet in the most destructive conflict ever waged are not, yet, inevitable.

Mr. Biden’s greatest challenge is geopolitical, not meteorological. His most important job is to prepare the American people to face the rapidly intensifying global crisis.

And he needs to move quickly.

The global temperature continues to rise.