Why Do We Get Cold Weather When the Climate Should be Warming?

While it’s widely understood that our planet’s climate is warming, there is a lot of confusion about how this influences our weather from year to year. If you kept up with the news at all between June and November of 2017 and 2018 (the time frame that defines the Atlantic hurricane season), you may remember seeing one headline after another with updates on the latest major storm to wreak havoc on the coastal communities of the southeast and Puerto Rico. Perhaps you even saw some heated discussions about whether or not these storms had proven the existence of climate change (click here for the latest evidence). With the cold snaps in the winter of 2018 and the polar vortex of 2019, though, many have publicly questioned why cold weather doesn’t disprove climate change. Despite the confusion in the media, the scientific consensus is clear – the global climate is warming, and the cold weather is part of it.

So if the global climate is warming, why did we get such cold weather during the 2018 winter months?

For those of us who live in the Midwest or on the East Coast, it goes without saying that winter 2018 was very cold – the new year in particular brought a blast of frigid Arctic air along with some of the coldest regional temperatures in decades. In Chicago, even spring got off to a painfully slow start after what already seemed like an endless winter, with continual snow storms into mid-April. In fact, April 2018 had the coldest start that Chicago’s seen in over a century! To many, the cold weather during that year’s winter season may seem to contradict the established warming trend in global temperatures. Just prior to the new year, President Trump facetiously remarked on Twitter that our country could benefit from global warming due to the cold, and that efforts to mitigate its effects are a waste of federal money. While the idea of a warmer climate may seem tantalizing during a particularly excruciating winter, global warming won’t necessarily lead to milder winters. But how on Earth (pun intended), you may ask, is this possible?

To see why, it is important to understand the difference between weather and climate. The frigid cold snaps we get every winter are weather events. For atmospheric scientists, weather describes conditions like temperature, humidity, and precipitation over a short period of time, such as days or weeks. In contrast, climate focuses on long-term trends in weather over the span of years, decades, centuries, or even millennia. So while the weather has been exceptionally cold in the Central and Eastern US these past couple winters, this was just a minor blip that is insignificant in the context of our global climate once we consider that our planet’s 20 warmest years on record have all occurred since 1995.

New Years Eve 2018 temperature anomalies over North America. (Click to expand.)

Weather and climate can even differ between regions. The eastern US can have its own weather patterns and, by extension, climate trends that may deviate from other regions and our planet as a whole. While it has been cold here in winter 2018, it had actually been the warmest winter on record for the Arctic, where temperatures in northern Greenland spent upward of 60 hours above freezing during the month of February!

While counter-intuitive, many researchers have found that extreme regional cold snaps may actually result from climate change, despite the overall warming trend at the global scale. Some scientists hypothesize that a weaker, less stable jet stream caused by climate change could allow cold air from the Arctic to spill into regions at lower latitudes, such as the Midwest (giving us 2019’s polar vortex, for example), only to be replaced by warmer air from further south. Overall, these strange weather patterns demonstrate that global warming is not distributed evenly around the world; while our planet’s average temperatures may be increasing as a whole, this may translate to unusually cold weather in some regions, and extremely warm weather in others. Here in Illinois, we’re often unlucky enough to fall in the cross-hairs of cold, arctic air.

If the global climate is supposed to get warmer by only 2 degrees celcius, why do the changes in weather seem so extreme?

You might be thinking, “It’s difficult to even feel that small of a temperature difference!”

Although our global climate has been steadily warming, regional weather can be more erratic. So while Earth’s average temperature may increase by 2 degrees Celsius by the end of the century, this does not mean that we will experience a future where it’ll be 2 degrees outside instead of 0 on a given day during the winter. During the ice age, our planet’s average temperature was only 5 degrees Celsius colder than it is today! Similarly to other complex systems like the human body, where a difference of only a few degrees in core temperature can mean the difference between life and death, small temperature changes in our planet’s climate can have a large impact on regional conditions.

Destruction left behind by Hurricane Maria in Puerto Rico in September 2017

Scientists are also predicting that we are going to experience more extreme weather events in our future as a result of climate change, costing money and lives. The 2017 Atlantic hurricane season, which was the most active since 2005 and the seventh most active on record dating back to 1851, is one striking example of the resulting impact. While it is difficult to say for certain whether individual storms were a direct result of climate change, it makes logical sense to connect the two given our understanding of hurricane formation: Hurricanes and tropical storms draw their energy from the heat of warm ocean waters; warmer sea surface temperatures create more energy and water vapor for storms to form. As global climate warms, so do the oceans, providing more fuel for catastrophic storms (including snow storms during the winter) once this heat reaches the atmosphere (read more about this here). The increasingly powerful storm surges, heavier rainfall, and higher wind speeds that result from these changes come at a cost: By the numbers, this past hurricane season season produced a total of seventeen named storms (ten of which were hurricanes), costing a total of over $200 billion in damages, making it the most expensive on record.

What does all of this mean?

While we know that our planet’s climate is warming overall, it is difficult for scientists to predict what the weather or climate will be like in specific regions over the decades to come. Meteorologists use computer models to forecast regional weather using real-time data, but these models are not accurate beyond a few weeks. While climate models can be used to make general long-term forecasts, they are less capable of accurately predicting what will happen within individual years or over smaller regions into the distant future. In the meantime, it is important not to make assumptions about global climate change based on the current weather in a specific region, which can change unpredictably from year to year. Nevertheless, it is reasonable to assume that adapting to climate change will become increasingly costly for many of us as our planet continues to warm.

Further Reading:

• Accuweather: Why Snow, Colder Weather Conditions Don’t Debunk Climate Change
• Yale Climate Connections: Why the Atlantic Hurricane Season was So Bad
• XKCD: Earth Temperature Timeline

Nathan Baskin recently graduated from the University of Chicago with a Masters of Science in geophysical sciences. You can learn more about him on his website and by following him on Twitter @NathanJBaskin.