This is global warming?

In Florida, the orange trees are freezing their buds off, and a prolonged, heartless chill has iced innocent iguanas. In Iowa, wind chills dropped to 35 below last week, and in Europe it snowed in Madrid and Paris. Energy prices are inching up, and the cold could put a squeeze on citrus prices.

Around here, a record wet and white December has yielded a premature harvest of potholes, and a poor man's glacier has barnacled the rocky cliffs lining the Schuylkill Expressway.

Granted, as Mike Halpert, deputy director of the government's Climate Prediction Center, observed: "It's winter. You wouldn't expect this in July." And temperatures will moderate this week.

But thanks largely to extraordinary developments in the Arctic, winter in parts of the Northern Hemisphere is off to an unusually vigorous start, and AccuWeather Inc. is on record as saying this could be the coldest winter in 25 years in the United States.

It's not that it's been all that extreme, said Fred Gadomski, a meteorologist at Pennsylvania State University; it just might seem that way because most recent winters have been remarkably gentle.

In fact, in the contiguous United States, 20 of the last 25 winters were warmer than long-term averages, including the last eight, according to the National Climate Data Center. Philadelphia just had its coldest first week of the year since 2001.

So what happened to global warming? "Climategate" notwithstanding, the data suggest that the planet continues to toast subtly - but on the order of tenths of degrees, hardly enough to snuff out winter as we know it, said Gadomski. "No human being on earth experiences the global average temperature," he said. "Even if we're warming, it doesn't cancel the cold."

Tony Cristaldi, a meteorologist in the National Weather Service office in Melbourne, Fla., would concur heartily. Temperatures in Melbourne dropped below freezing on four consecutive days last week. The exceptionally long cold spell has some Floridians muttering through their chattering teeth - and, Cristaldi said, "I'm one of them."

The Florida chill evidently has taken a toll on the state's immense - and largely unwanted - invasive iguana population. Temperatures below 40 can be fatal to the cold-blooded lizards, said Tiffany Snow, a biologist with the Florida Fish and Wildlife Conservation Commission. She said she received several calls from Palm Beach and Boca Raton residents who reported that stiffened iguanas had fallen from trees and branches.

Meanwhile, the commission has removed more than 500 sea turtles from cold waters to safer locations.

Temperatures in the Sunshine State last week were averaging 20 degrees or more below normal, part of a corridor of frigid air that had plunged northwest to southeast across the continent. The Mid-Atlantic and the Northeast have been on the fringe of the cold, Gadomski said.

Montana has been in the icy thick of it for weeks. In most places it was the coldest December since 1983, said Ben Schott, a meteorologist at the Great Falls office.

The cold there was somewhat of a surprise because a strong El Niño, an unusual warming of the tropical Pacific, had erupted in October. Typically, an El Niño winter means relative warmth in Montana. In their winter outlook, Halpert and his Climate Prediction Center colleagues called for all of Montana to be above normal this winter.

"A lot of people are screaming, 'El Niño, where are you now?' " Schott said.

So far, however, El Niño has been upstaged by the so-called Arctic Oscillation, or A.O., an air-pressure pattern that can have profound impacts on winter in the United States and Western Europe. The A.O. index tracks pressure changes between the polar region and the latitudes closer to Philadelphia. When the pressures are higher in the Arctic, cold air can be pushed southward, and the index is said to be negative.

In December, the index was at its lowest level since the historically cold January of 1977. In the first week of January this year, it plunged even further. "There is no doubt that this A.O. component has been extreme," Gadomski said.

Halpert believes that the warming winds from the west generated by El Niño will moderate temperatures this week, dispelling some of the bitter-cold air in the United States.

But WSI Corp., a forecasting company in Massachusetts that serves energy clients, is calling for virtually the entire country to be cold in February. The company said the cold likely would draw down energy supplies and raise prices.

One factor in the frosty outlook is relatively cold water in the North Pacific, said forecaster Todd Crawford of WSI. That was not the case during the El Niño events during the warm run of winters that began in the mid-'80s, Gadomski said.

"Certainly not all El Niños are created equal," he said, "and they are not the only player on the chessboard."

If anything, the winter of '09-10 has underscored the complexities of the atmosphere, he added. Just knowing that the planet is slowly warming isn't much help in figuring out precisely who is going to get hammered with blizzards or heat waves.

"There's no doubt that the planet is warmer than it was 100 years ago," Gadomski said. "The only really important thing at any given time is how the warmth is distributed across the globe.

"This is among the least-well-understood parts of how weather and climate will change in the years ahead."

EndText