Snow in Cairo – First in 112 years

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If you look at that picture you see the magnificent view of palms in the middle of snow. That is egypt and it’s snowing for the first time in 112 years. Of course didn’t take long for people to wonder if this has anything to do with climate change.

http://instagram.com/p/h26ZA0l3DY

Is it about climate change?

However, there’s a misconception right there. Local weather is dependent on many variables. You can see one variable in the following video:

http://www.npr.org/2013/09/25/225754902/wild-weather-tied-to-unusual-jet-stream-activity

This is the so called jet stream. A strong current of air in the upper troposphere that can persist for days, which is pretty stable for a weather event. With a strong influence on the weather in the US, according to NASA:

When we look at extreme weather events like sudden snow in egypt, you cannot point this to climate change. Nevertheless, the link between these events and climate change is increasingJames Hansen, Makiko Sato, Reto Ruedy, Andrew Lacis, and Valdar Oinas (2000). Global warming in the twenty-first century: An alternative scenario PNAS DOI: 10.1073/pnas.170278997. These changes are measured over the course of at least 30 years. This event will count towards a statistic made over the course of this time and from that we can derive if these anomalies increaseJames Hansen, Makiko Sato, and Reto Ruedy (2012). Perception of climate change PNAS DOI: 10.1073/pnas.1205276109.### Why dows it snow?
Now I was wondering, why everyone was talking about global warming and then snow counts towards that statistic. This one needs a little statistics to understand. The following graphic shows how different variations have different outcomes. The last panel shows an increase in mean and variance, which leaves close to no change in overall cold weather events.

Schematic showing the effect on extreme temperatures when (a) the mean temperature increases, (b) the variance increases, and (c) when both the mean and variance increase for a normal distribution of temperatureIPCC.

Concluding you cannot say if this is really related to climate change. This does neither prove nor disprove global warming (there’s enough scientific evidence to back global warming upScientific Consensus.) and it shouldn’t be used in this context. However, it’s likely that such surprising events happen more often as climate change progresses.

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Jesper Dramsch

PhD Student at The Way of the Geophysicist
... is a geophysicist by heart. He works at the intersection of machine learning and geoscience. He is the founder of The Way of the Geophysicist and a deep learning enthusiast. Writing mostly about computational geoscience and interesting bits and pieces relevant to post-grad life.
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