Winter is Warming: The Symptoms of “Warming Winter Syndrome”
One of the most noticeable indicators of Earth’s changing climate is the fact that winter is warming at a faster rate than other seasons. This phenomenon, which I refer to as “warming winter syndrome,” brings about a cascade of changes, including ice storms and rain in regions that were once consistently below freezing.
Wintertime warming is a clear reflection of the accumulation of global heat. While direct heat from the sun is weak during winter, storms and shifts in the jet stream bring warm air from more southern latitudes into the northern United States and Canada. As global temperatures and the oceans warm, this stored heat has an impact on both temperature and precipitation.
The evidence of this warming can be seen in changes to growing seasons, as reflected in recent updates to plant hardiness zones. These maps depict the northward and, in some cases, westward movement of freezing temperatures in eastern North America.
The shifting freezing line between snow and rain can result in unexpected ice storms in places and at times when communities are unprepared to handle them, as was the case in several parts of the United States in early 2024.
Ice storms and wet snow are becoming more prevalent as freezing temperatures move northward. In regions where historically it was reliably below freezing from early December through February, the transition to freezing temperatures can now extend as far north as Lake Superior and southern Canada. This change in temperature leads to an increase in ice storms in colder regions.
The character of snow also changes near the freezing line. When the temperature is well below freezing, snow is dry and fluffy. However, near freezing temperatures, snow becomes wet and heavy, sticking to tree branches, turning roads into slush, and bringing down power lines.
As the climate continues to warm, individual snowstorms can lead to more intense snowfalls due to the warmer and wetter conditions in which they form. However, as temperatures rise even further in the future, the balance will shift towards rain, resulting in a decrease in the overall amount of snow.
In fact, winter rain is already becoming the dominant type of precipitation on the warmer side of the freezing line, and this trend is expected to continue. With warmer oceans acting as a major source of moisture, the Eastern United States can anticipate increased winter precipitation over the next 30 years. Therefore, wet and soggy winters are more likely in the future.
The rapidly changing climate poses significant challenges for communities when it comes to planning for water supplies and extreme weather events. It is becoming increasingly difficult to rely on current weather patterns as a basis for future planning.
Snow will not persist as late into spring in many regions, affecting water supplies that rely on snowpack throughout the year. Rain falling on snowpack can speed up melting, trigger flooding, and alter the flows of creeks and rivers. This has already been observed in changing runoff patterns in the Great Lakes and flooding on the East Coast in January 2024.
Road planners also face challenges due to the increased rate of freeze-thaw cycles that can damage roads in regions unaccustomed to such rapid shifts in temperature.
Another notable effect occurs in the Great Lakes, where the freezing process is no longer as early or as complete as in the past. This leads to increased lake-effect snow in regions where the wintertime air temperature is still below freezing. However, as the air temperature approaches the freezing line, these events are more likely to be rain and ice rather than snow.
Despite these changes, cold weather will still occur, with Arctic air occasionally dipping down into the United States. This can cause flash freezing and fog when warm, wet air surges back over the frozen surface.
The consequences of warming winters extend beyond the environment and have significant impacts on economies. Many industries and crops rely on cool winter temperatures, and freezing weather is essential for controlling pests. Any changes in temperature and water conditions can disrupt the conditions in which plants and animals thrive.
These changes also affect outdoor sports and recreation, commercial fisheries, and agriculture, leading to enormous consequences for ecosystems and our relationship with them. Traditions such as ice fishing may be lost, and people everywhere will need to adapt to the changing climate.
It is clear that “warming winter syndrome” is a set of consistent and robust symptoms on a planet experiencing a fever. While some may see the benefits of less snow to shovel and lower heating bills, the economic and ecological impacts cannot be ignored. It is essential for communities and individuals to prepare and adapt to the significant changes that come with a warming winter.
Richard B (Ricky) Rood is a professor of Climate and Space Sciences and Engineering at the University of Michigan.
This article was originally published on The Conversation.
