With unusually frigid weather gripping much of the Eastern United States this week, President Donald Trump took to Twitter on Thursday to cast doubt on the reality of climate change, but he appeared unaware of the distinction between weather and climate.

In his post, Trump wrote: “In the East, it could be the COLDEST New Year’s Eve on record. Perhaps we could use a little bit of that good old Global Warming that our Country, but not other countries, was going to pay TRILLIONS OF DOLLARS to protect against. Bundle up!”

Indeed, parts of the East Coast are bracing for record-breaking New Year’s Eve temperatures. New York City, for example, is forecast to experience its coldest New Year’s temperatures since the 1960s. But Trump’s tweet made the common mistake of looking at local weather and making broader assumptions about climate.

Climate refers to how the atmosphere acts over a long period of time, while weather describes what’s happening on a much shorter time scale. The climate can be thought of, in a way, as the sum of long periods of weather.

Or, to use an analogy Trump might appreciate, weather is how much money you have in your pocket today, whereas climate is your net worth. A billionaire who has forgotten his wallet one day is not poor, anymore than a poor person who lands a windfall of several hundred dollars is suddenly rich. What matters is what happens over the long term.

On Thursday, parts of the United States were roughly 15 to 30 degrees Fahrenheit colder than average for this time of year. But the world as a whole was about 0.9 degrees Fahrenheit warmer than the average from 1979 to 2000.

And while climate scientists expect that the world could warm, on average, roughly 2 to 7 degrees Fahrenheit by the end of the century — depending on how fast greenhouse-gas emissions rise — they don’t expect that to mean the end of winter altogether. Record low temperatures will still occur, they’ll just become rarer over time.

Indeed, that’s already been happening. One 2009 study found that the United States saw roughly as many record highs as record lows in the 1950s. By the 2000s, there were twice as many record highs as record lows. Severe cold snaps were still happening, but they were becoming less common.

The tweet also took an implicit swipe at the Paris climate accord, which Trump has vowed to abandon. In announcing that the United States would withdraw from the agreement among almost 200 nations to collectively rein in greenhouse gas emissions, Trump lobbed a similar charge that the deal put a burden only on the United States.

The United States under President Barack Obama pledged $3 billion over four years to the Green Climate Fund, aimed at helping countries build resilience to extreme weather and develop clean energy. Japan has paid about $1.5 billion into the fund, Britain $1.2 billion and France and Germany about $1 billion each. Developing countries like Mexico, Chile and Indonesia have also contributed.

Trump has made a habit of airing his climate skepticism on Twitter, posting comments on “climate change” or “global warming” more than 100 times since 2011. Thursday’s tweet appeared to be the first time he addressed the issue head-on since becoming president, however. The last time he fired off a tweet on global warming was more than two years ago, when he declared: “It’s really cold outside, they are calling it a major freeze, weeks ahead of normal. Man, we could use a big fat dose of global warming!”

The climate may be changing, but some jokes stay the same.

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