 Prior to 1952, if you wanted to fly from Tokyo to Honolulu, it took you around 18 hours. But in 1952, airlines figured out a way to make the same flight in just 11 hours. How did they do it? Did they discover a new type of fuel or develop a sleeker jet? No, they simply used something that had been there all along, the jet stream. The jet stream is a narrow band of strong winds near the top of the troposphere, about 10 kilometers above the Earth's surface. It's like a fast-moving river of air. The wavy shape and the location of the jet stream changes constantly with the weather. Under the ridges formed by the jet stream are warm, dry conditions. Sometimes the ridges can take on such a shape that it opens the door to the poles and allows for cold, arctic air to blow down through the trough. It's like leaving the refrigerator door open, letting cold air leak into the kitchen. This cold air streams down from the pole and pools in the area north of the trough. This weather pattern, sometimes called a blocking pattern, is usually slow to move. So the cold air persists in what we call the cold air outbreak. Something to note is that this cold air was previously sitting comfortably over the traditionally cold areas, the poles. The weather pattern brings the cold air down to lower latitudes, which usually means the poles get unusually warm. In other words, when we experience cold temperatures at low latitudes, it's a bit like a balancing act. The warm air doesn't just disappear, it just moves to other places. So that's how the jet stream and cold air outbreaks work. However, one myth distorts the science of global warming, and I'm sure this is one you've heard quite a few times. Every winter, when conditions set in, people say it's cold out, so much for global warming, implying that record cold winters disprove global warming. This uses the technique of cherry picking, a weather event in a local region instead of looking at the global picture. When cold air leaks down from the poles into your region, it doesn't change the fact that global warming is happening. It usually means your area has just exchanged air masses with another place on earth. It's important to remember that the definition for global warming is the global average temperature change, not the temperature you feel at your local area. One of the hot topics in climate science right now asked the question, is climate change causing these events to take place more often? Scientists are digging into the observations, as well as computer simulations of future climate to try to find the answer to this question. One hypothesis is that climate change is creating the conditions for a slower, wavier jet stream. Here's why. The strength of the jet stream is based on a force called the pressure gradient force. This force's strength depends on the difference in temperature across the polar front, the area of tight contrast between the warm tropical air and the cold polar air. One of the most interesting pieces to the global warming story is that not everywhere on earth is warming at the same rate. The Arctic is warming faster than any other region on earth. We call this Arctic amplification. There are several reasons for it. The biggest contributor is a positive feedback or self-reinforcing cycle involving the melting of Arctic snow and ice. Global warming has caused less snow and ice cover in the Arctic. This replaces white reflective surfaces with dark absorptive surfaces that absorb more sunlight and get warmer. This melts even more snow and ice, causing more absorption and causing even further warming. This cycle has caused the Arctic to warm up twice as fast as the global average. Because the Arctic is warming faster, the cold side of the jet stream is a few degrees warmer than usual while the warm side hasn't warmed up as much. This means the strength of the difference in temperature becomes smaller, weakening the pressure gradient force. Therefore, the winds up in the jet stream could become slower. Occasionally, a consequence of this slowing is that the jet stream takes on a really large amplitude wave pattern, which can lead to more of these blocking patterns or so the hypothesis goes. Now, it's worth noting that these cold events can take place with or without Arctic amplification and global warming, but climate scientists are exploring whether we might have more of these blocking pattern events leading to cold air outbreaks than before. In time, the answer might become more obvious. Time will tell. The winter of 2013-14 in the United States was a great example of a blocking pattern in the jet stream. The eastern half of the United States experienced one of the harshest, coldest winters on record. At the same time, the western US experienced one of the warmest and driest on record, leading to an extensive drought in the California region. It's a great example of that balancing act with one region colder while another region is warmer. Meanwhile, looking at the whole planet, we set the record for the warmest year on record in 2014. This can be confusing for people in the eastern US who had weeks of school canceled due to low wind chill values as the door to the Arctic refrigerator stayed open for weeks. But we have to remember the big picture, the global picture when we think about global warming. A cold winter in one region doesn't disprove global warming. You have to look at the big picture.