For years, climate contrarians have pointed to snowfall and cold weather to question the scientific reality of human-induced climate change.
Such misinformation obscures the work scientists are doing to figure out just how climate change is affecting weather patterns year-round.
Understanding what scientists know about these effects can help us adapt. And, if we reduce the emissions that are driving climate change, we can dramatically reduce the pace of change and better prepare for the consequences in the future.
What Is the Relationship Between Weather and Climate?
Weather is what’s happening outside the door right now; today a snowstorm or a thunderstorm is approaching. Climate, on the other hand, is the pattern of weather measured over decades.
NASA and NOAA plus research centers around the world track the global average temperature, and all conclude that Earth is warming. In fact, the past decade has been found to be the hottest since scientists started recording reliable data in the 1880s. These rising temperatures are caused primarily by anincrease of heat-trapping emissions in the atmosphere created when we burn coal, oil, and gas to generate electricity, drive our cars, and fuel our businesses.
Hotter air around the globe causes more moisture to be held in the air than in prior seasons. When storms occur, this added moisture can fuel heavier precipitation in the form of more intense rain or snow.
At the same time, because less of a region’s precipitation is falling in light storms and more of it in heavy storms, the risks of drought and wildfire are also greater. Ironically, higher air temperatures tend to produce intense drought periods punctuated by heavy floods, often in the same region.
These kinds of disasters may become a normal pattern in our everyday weather as levels of heat-trapping gases in the atmosphere continue to rise.
The United States is already experiencing more intense rain and snowstorms. The amount of rain or snow falling in the heaviest one percent of storms has risen nearly 20 percent, averaged nationally — almost three times the rate of increase in total precipitation between 1958 and 2007.
Some regions of the country have seen as much as a 67 percent increase in the amount of rain or snow falling in the heaviest storms — and an updated version of this figure from the draft National Climate Assessment suggests this increase may have risen to 74 percent between 1958 and 2011.
Overall, it’s warming, but we still have cold winter weather.
The seasons we experience are a result of the Earth’s tilted axis as it revolves around the Sun. During the North American winter, our hemisphere is tilted away from the Sun and its light hits us at a different angle, making temperatures lower.
While climate change won’t have any impact on Earth’s tilt, it is significantly shifting temperatures and causing spring weather to arrive earlier than it used to. Overall, spring weather arrives 10 days earlier than it used to, on average. “Spring creep" is something scientists projected would happen as the globe continues to warm.
The Arctic Connection: A Look at Recent North American Winters
Winters have generally been warming faster than other seasons in the United States and recent research indicates that climate change is disrupting the Arctic and ice around the North Pole.
The Arctic summer sea ice extent broke all records during the end of the 2012 sea ice melt season. Some researchers are pointing to a complex interplay between Arctic sea ice decline, ocean patterns, upper winds, and the shifting shape of the jet stream that could lead to extreme weather in various portions of northern mid-latitudes — such that some places get tons of snow repeatedly and others are unseasonably warm.
In the Arctic, frigid air is typically trapped in a tight loop known as the polar vortex. This super-chilled air is not only cold, it also tends to have low barometric pressure compared to the air outside the vortex. The surrounding high-pressure zones push in on the vortex from all sides so the cold air is essentially "fenced in" above the Arctic, where it belongs.
As the Arctic region warms faster than most other places, however, the Arctic sea ice melts more rapidly and for longer periods each year, and is unable to replenish itself in the briefer, warmer winter season. This can destabilize the polar vortex and raises the barometric pressure within it.
For two winter seasons (2009/2010 and 2010/2011), the polar vortex was notably unstable. In addition, another measurement of barometric pressure — the North Atlantic Oscillation (NAO) — was in negative mode, weakening part of the barometric pressure "fence" around the polar vortex. This instability allows the cold Artic air to break free and flow southward, where it collides with warmer, moisture-laden air. This collision can produce severe winter weather in some regions and leave milder conditions in other parts of the northern hemisphere.
The winter of 2009/2010 recorded the second lowest negative phase of the NAO since the 1970s, which helps to explain the record snowfalls across the northeastern United States. The 2010/2011 winter also trended toward a strong negative phase.
During the 2011/2012 winter, there was a shift in the position of the jet stream, which separates cold arctic air from warmer air. Typically New England, the Great Lakes, and parts of the Great Plains sit north of the jet stream and remain cold in the winter season. However, the 2011/2012 winter jet stream position meant these regions were south of it for most of the winter, which helped produce the fourth warmest U.S. winter on record.
The lack of snowfall and snowpack for the winter of 2011/2012 and the following spring was a precursor to the large drought episode that impacted two-thirds of the nation during the summer and autumn of 2012.
In the following winter of 2012/2013, the polar vortex was more stable, with the NAO in December and January around neutral, and moderately high in February. The weather systems were not dominated by the polar vortex but equally influenced by several other oceanic and atmospheric drivers, including the Pacific North American pattern and the Arctic Oscillation.
Even though hundreds of monthly precipitation records were broken across the United States in February 2013, the winter of 2012/2013 was characterized by a complex interplay of atmospheric drivers, with no single factor dominating the storm tracks and the broader scale circulation.
The North American winter of 2013/2014 is shaping up to be a complex interplay among the upper atmosphere circulation over North America and the ocean conditions in the East and North Pacific with other factors playing a minor role according to November patterns. December 2013 data are still being analyzed; preliminary indicators suggest that the early season snows that obscured football games played in the Eastern U.S. and caused transportation disruptions in early December were in part linked with a deep penetration of the jet stream over the center of North America.
Scientists are looking into how the jet stream pattern shifts in recent years have influenced where winter sets in hardest in the Northern Hemisphere, though it’s not clear how much impact this trend will have in the future, especially as the Arctic ice continues to lose mass.
It’s Not Too Late
The choices we make today can help determine what our climate will be like in the future. Putting a limit on heat-trapping emissions, encouraging the use of healthier, cleaner energy technologies, and increasing our energy efficiency are all ways to help us to avert the worst potential consequences of global warming, no matter what the season.
This article was originally published on the Union of Concerned Scientists and was republished with permission.