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    The frozen, snowbound Upper Midwest as seen from space on Jan. 29. Image: CIRA/RAMMB
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    Graph data: The 1980-2015 seasonal cycle anomaly in MERRA2 along with the 95% uncertainties on the estimate of the mean. Figure: NASA/GISS/GISTEMP

Yes, it’s cold. But the earth is still warming.

Scientists agree: we need to differentiate between weather and climate.
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Every winter brings some bitterly cold days, and it thus seems natural that each winter we ask why this one is so cold. Maybe the coldest we’ve had!

And in the summer, it’s the same: isn’t this the worst July ever? Isn’t it hotter than last year?

Most of the time these feelings are just reactions to the freezing cold or blazing heat combined with our painfully short short-term memory. But every once in while, we really do have those record-breaking events. We’ve just had one this week.

Over the last few days, those in the Midwest and upper Plains have experienced dangerously cold wind chills. Some cities have seen temperatures drop close to the lowest ever recorded. Cities like Chicago and Milwaukee had been preparing for the deep freeze, but even so, when the cold arrived, life across the region came to a standstill.

More than 2,000 flights in or out of the frozen Midwest have been canceled so far. Eight deaths have been reported. The US Postal Service stopped deliveries in some states. Workers were sent home, meetings canceled, parties called off.  Some states declared states of emergency.

You may be following the weather channels where meteorologists blame the polar vortex for this cold weather. “Polar vortex” is a fancy name for the large area of low pressure and cold air surrounding the earth's North and South poles. And vortex simply refers to the counter-clockwise flow of air that keeps that frigid air close to the poles.

During some winters—like this one--the polar vortex will become less stable and expand, sending cold Arctic air southward over the United States with the jet stream.

When that happens, super cold air locked around the north pole expands all over the northern plains and Midwest.  Don’t worry; it’s mostly over by now. The polar vortex is a short-term effect.

But given all these frigid nights, one might wonder: Doesn’t all this winter weather around the country mean that climate change is a hoax?

The short answer is: of course not. Just because some of us are suffering through a particularly cold winter doesn’t refute the fact that the earth is warming.

Scientists agree: we need to differentiate between weather and climate.

Weather refers to atmospheric conditions that occur locally over short periods of time—from hours to days or weeks, even seasons. When a neighbor remarks, “It’s been a wet spring, huh?” that’s a conversation about weather.

Climate is the long-term trend of atmospheric conditions across large regions, even the whole planet. Climate change is used to describe a long-term change in global temperatures and weather patterns. Global warming refers to a long-term rise in the average temperature of the earth’s climate system.

The average temperature of Earth’s surface and the atmosphere has varied throughout the earth’s history. Warm spells and cold ones have alternated. However, in recent years a totally new pattern has been observed in scientific research. We can observe that our planet is warming much faster than it ever has before.

This is not a guess or a question of beliefs. The measured mean temperature clearly shows that it is increasing. And it’s not just that the global temperature is increasing. The average temperature in the US also follows the trend of the global average temperature increases.

The obvious question we then must answer is: what’s making our earth warmer?

The major source of heat energy in our planet is the sun. Sunlight shines on the Earth's surface, carrying light and heat. This energy is absorbed by the surface of the earth and then radiates back into our atmosphere. In the atmosphere, molecules know as greenhouse gases, primarily carbon dioxide, trap some of the heat while the rest escapes into space.

The more greenhouse gases concentrate in the atmosphere, the more heat gets locked in the molecules. This heats up our planet and thus increases the global temperature.

The signs of global warming are various and more complex than just an increasing average temperature. Some of the extreme weather events of all kinds—from snowstorms, hurricanes, droughts, and floods—are side effects of it. If the earth heats up much more, it’s possible the impacts on our climate, ecosystems, agriculture—life on Earth as we know it—will be very, very different.

If we’re serious about preventing those catastrophic events to the degree that we can, we’ve got to answer another question: who or what is producing greenhouse gases?

That’s an easy question to answer: humans. We’ve got to look at ways to reduce our contribution of greenhouse gases, especially carbon dioxide, if we don’t want to profoundly alter the earth our grandchildren inherit.

So yes, it’s been a cold winter. But the earth is still warming, and we still have to do something about it.


 (Dr. Yadav Pandit is an experimental nuclear physicist currently working at Allen Community College as a physical science instructor. He writes a column of general interest in science for the Register.)

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