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Opacity

Freeze-Thaw Days

Key messages:

  • Number of freeze-thaw days decreases almost everywhere at +2°C global warming
  • Exceptions are modest increases at high altitudes and latitudes
  • Generally impacts are positive as crossing below zero degrees creates hazardous conditions

Why is the content of this map important?

Freeze-thaw days are days during which temperatures cross below the zero degree threshold. These can have serious and costly impacts on aviation, roadways and railways. This is largely due to the expansion/contraction of materials, which leads to cracking and deformation. On roadways and runways the most dangerous ice conditions also occur around the zero degree threshold.

Which sectors are affected by this result?

The results are important for the transportation sector, especially transport infrastructure design and maintenance; particularly road, rail and air.  The projected changes are actually good news for most of Europe where zero-degree crossings are problematic under present conditions.

What is shown on the maps?

The current map shows that freeze-thaw days are most common in northern Europe with anywhere from 30-60 freeze-thaw days per year. The +2°C period already shows decreases, on average, of over 15 days per year in northern Europe and the near disappearance of the phenomenon at lower latitudes. The few areas that do show an increase are modest, only being a handful of days.

Details and further information:

We have defined freeze-thaw days following the description given by Schmidlin et al. (1986). A day is considered a freeze-thaw day if the daily minimum temperature is less than or equal to -2.2°C and the maximum temperature is above zero. Then the number of these days is calculated over each year. There are many alternative definitions. The argument for our approach is that temperatures between zero and -2°C do no constitute a hard freeze and impacts on vegetation and infrastructure are modest. Adoption of alternative definitions does not change the results or key messages.

Additional information:

Author:

Stefan Sobolowski

Uni Research AS (UniRes), Norway