TOO MUCH, TOO SOON

Forget autumn: Winter is coming for the slopes of United States.

It’s only November, and half the U.S. is blanketed in snow—six feet deep and counting in and around Buffalo, New York—while parts of the Deep South have been waking up to temperatures that are just above freezing.

For years, climate contrarians have pointed to snowfall and cold weather to question the scientific reality of human-induced climate change.

At first glance, asking whether global warming results in more snow may seem like a silly question because obviously if it gets warm enough, there is no snow. Consequently, deniers of climate change have used recent snow dumps to cast doubt on a warming climate from human influences. Yet they could not be more wrong.

To understand the connection, we need to look at the conditions that make the heaviest snowfalls.

There is a saying, “too cold to snow”! Of course, this is a myth but it has a basis in fact because the atmosphere gets freeze dried when it is very cold. That’s because the amount of moisture the atmosphere can hold depends very strongly on temperature. Under cold conditions, the snow is likely to consist of very small crystals and sometimes is very light and fluffy and like “diamond dust”.

The physics behind this phenomenon is governed by a basic law that tells us the maximum amount of moisture in the atmosphere increases exponentially with temperature – that is, the warmer the atmosphere, the more moisture the air can hold and thus, the more potential for precipitation.

For most conditions at sea level, there’s a rule of thumb that says the atmosphere can hold 4% more moisture per one degree Fahrenheit increase in temperature. Some complications come in as the ice phase enters, but we set those aside for now. That translates into a big difference in moisture across temperature differences: At 50°F (10°C) the water-holding capacity of air is double that at 32°F (0°C) and at 14°F (-10°C) the value is only 24% that at 50°F.

Some recent research has shown that increasing surface temperatures and reductions in Arctic sea ice may produce atmospheric circulation patterns that are favorable for winter storm development in the eastern United States. Most notably, a greater prevalence of high pressure blocking patterns over the North Atlantic that result in cold outbreaks in the eastern United States along with slower moving systems can further exacerbate the persistence and severity of a storm.

Global warming is also causing warmer spring weather to arrive earlier than it used to. Overall, spring weather is already arriving 10 days earlier than it used to.  A recent study estimated that the median onset of plant growth in spring will happen three weeks earlier over the next century, as a result of rising global temperatures.

Put another way: whether warming causes more or less precipitation varies by region, but it changes the balance between snow and rain. As long as it stays below freezing, the snow dumps are bigger, but the snow season shrinks at both ends of winter. So more time is spent raining: skiers in some regions benefit in mid-winter but with a shorter ski season.

Because the increased moisture in the storm can also feedback and amplify the storm itself, the extra snow can easily be order 10% or more from the climate change component.

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