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| Freezing weather brings 'warm-ice' warning | Freezing weather brings 'warm-ice' warning |
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| Freezing temperatures across the UK – as low as minus 13ºC was forecast for some parts of the country this week – have caused the usual winter travel chaos for trains, car drivers and pedestrians. But have you ever wondered why the ice on the ground tends to be so slippy, while if you pick up an ice cube from your freezer it sticks to your fingers? It's all in the temperature, says Professor Chris Clark of Sheffield University. | Freezing temperatures across the UK – as low as minus 13ºC was forecast for some parts of the country this week – have caused the usual winter travel chaos for trains, car drivers and pedestrians. But have you ever wondered why the ice on the ground tends to be so slippy, while if you pick up an ice cube from your freezer it sticks to your fingers? It's all in the temperature, says Professor Chris Clark of Sheffield University. |
| "Most people think of ice as cold," explains the glaciologist. "Those who know ice know that some is cold and some is warm. Cold ice, say -5C, is actually fairly grippy." This is the ice that "burns" your hand when you try to put it in the cocktail shaker. But the ice on the street is usually quite different. "Warm ice, say at -1C or nearly 0C, will have a thin film of meltwater on its surface, and it is this that makes it so slippy." The water lubricates the interface with the ice below, reduces friction and is what causes you to fly head-over-heels, to the amusement of passers-by. | "Most people think of ice as cold," explains the glaciologist. "Those who know ice know that some is cold and some is warm. Cold ice, say -5C, is actually fairly grippy." This is the ice that "burns" your hand when you try to put it in the cocktail shaker. But the ice on the street is usually quite different. "Warm ice, say at -1C or nearly 0C, will have a thin film of meltwater on its surface, and it is this that makes it so slippy." The water lubricates the interface with the ice below, reduces friction and is what causes you to fly head-over-heels, to the amusement of passers-by. |
| The only good thing that can be said about recent temperatures is that they have been so low in many places that the ice has remained "grippy" rather than slippy, making it slightly safer to go out on. It is the same principle that keeps glaciers glued to mountainsides. If the bedrock below is not cold enough, relatively warm ice at the bottom can slide over the rocks instead, causing it to flow downhill slightly faster – a symptom of global warming. | The only good thing that can be said about recent temperatures is that they have been so low in many places that the ice has remained "grippy" rather than slippy, making it slightly safer to go out on. It is the same principle that keeps glaciers glued to mountainsides. If the bedrock below is not cold enough, relatively warm ice at the bottom can slide over the rocks instead, causing it to flow downhill slightly faster – a symptom of global warming. |
| Anyone worried about venturing outside in the cold snap should beware the thaw most of all, according to Clark. While the ice retains its grip, pedestrians have less to fear, but when it starts to look "less frosty", beware. But, as a seasoned glaciologist of nearly 30 years' standing, he has some advice. "Take shorter steps." | Anyone worried about venturing outside in the cold snap should beware the thaw most of all, according to Clark. While the ice retains its grip, pedestrians have less to fear, but when it starts to look "less frosty", beware. But, as a seasoned glaciologist of nearly 30 years' standing, he has some advice. "Take shorter steps." |
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