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Weather, Climate, Extreme Weather and Chaos Theory

How does climate relate to the weather?

We like to talk about the weather, to complain about its variability and to blame the weather forecasters for getting it wrong. But what is ‘climate’, and how does the weather we experience on a day-to-day basis relate to climate change, a subject which is increasingly dominating our newspapers and television screens? Why is it that we can’t make a perfect weather forecast? And how can we hope to predict the climate of the 21st century, when we can’t say what the weather will be doing in a week’s time?

So, how does the climate relate to the weather we experience on a day-to-day basis? We know from experience that the weather can be very different from one day to the next, let alone from one year to the next, without any change in the climate.

Surprisingly, dice are a good way to think about the difference between weather and climate…

The animation below allows you to choose how many times to roll a dice and then see how often you get each of the six sides. Try a low number of rolls, then try some larger number of rolls and see what happens:

Throw the die a few hundred times. What is the average (mean) of the scores? The more throws, the closer the average gets to 3.5. If you were to throw the die one more time, you would not be able to predict the number that the die would land on, as the probability of throwing each number is the same. However, you could be very confident that the mean would still be 3.5.

But what has this got to do with weather and climate?

What if we associate weather types (for example, cloud cover) with each number on the die?

Try rolling the dice in the animation, again explore what happens as the number of rolls increases.

As when there were numbers on the sides of the die, you can’t predict what the weather will be on the next throw. Climate is defined as being the average of the weather over a long (typically 30 years) period of time. The ‘climate’ of this die is 50% cloud cover. A single throw of 0% or 100% cloud cover won’t affect the climate very much if you are taking the average of 100s of throws. In the same way we can have a very hot summer one year, and a very wet one the next, without the climate, the weather we expect to happen, necessarily changing.

“Climate is what we expect, weather is what we get”

So why do the weather forecasters never get it totally right? Mostly because the weather is a ‘chaotic’ system.

Very small changes to the starting conditions can lead to completely different weather patterns developing. This observation led Ed Lorenz to suggest that the flap of a butterfly’s wings in the Amazon rainforest could lead to a tornado in Texas. It is very unlikely, but it could.

This means that, to make a perfect weather forecast, we need to know what the atmosphere is doing currently, down to the scale of individual butterflies flapping their wings, which is obviously impossible!

So, since tiny changes in the starting conditions of a weather system can make significant differences to the outcome, when making a forecast we have to try to take into account what might be happening now, as well as what might happen in the future to affect the atmosphere. The best we can do is to produce a range of forecasts, with some indication of what is most likely, or least likely, to happen.

To help illustrate this, consider throwing two dice instead of one:

With two dice, the probability of throwing a combined score of a number between 2 and 12 is not the same. There is only one combination of number that would give you a 2 or a 12 (two 1s or two 6s respectively) but, for example, for a combined score of 4 you could throw a 3 and a 1, two 2s or a 1 and a 3 – so you are 3 times as likely to throw 4 as 2 or 12. There are most possible ways of throwing a combined score of 7, and no way at all of throwing a 1 or 13 or more.

Move the slider to pick a number and throw the dice a large number of times. Notice the shape of the graph that is produced – the middle numbers are rolled more often than the smallest or largest numbers.

This sort of shape of ‘bell shaped’ graph is very common. For example, temperature measurements will often show a similar distribution, although temperature can of course take any value, not just the numbers one to twelve.







In this way, the results of many weather and climate forecasts can be combined to show what is most likely to happen, what is unlikely to happen and what almost definitely won’t happen.

But what about extreme events? How will the likelihood of an extreme event change as the climate warms? It is never possible to attribute one particular event to a particular cause. To go back to the dice example, you could load a die so that sixes occur twice as often as normal. But if you were to throw a six using this die, you could not blame it specifically on the fact that the dice had been loaded. Half of the sixes would have occurred anyway, even with a normal die. Loading the die just doubles the odds of throwing a 6.

In general, if the climate warms, the whole bell-shaped curve of temperature for a particular place shifts to warmer temperatures:

Graph 1

Taken from the Synthesis report on Climate Change, 2001, ipcc.ch

Record hot events are more likely in a warmer world, and record cold events are less likely.

So, for example, we can say that the hot summer of 2003, which killed 22,000 – 35,000 people in central Europe, is twice as likely because of the global warming that has resulted from the man-made emissions of greenhouse gases. By 2050, we can expect summers as hot as that every other year.

Similarly, in the U.K., we can expect the number of extremely rainy days, with associated flooding, to increase. Already, the kind of rainfall that you could have expected once every 30 years in the 19th century is happening once every 12 years now. By the end of the century, it could be expected every 4 years.

So, to summarise:

  • Even with perfect forecasting techniques, we could never say exactly what the climate will do over the next century. This is because:
    • weather is chaotic
    • we don’t know how the world will develop and how much greenhouse gas will be emitted
    • We don’t know what other, natural, factors may affect the climate in the future – volcanic eruptions, changes in solar activity etc.
  • We can, at best, say what the climate is most likely to do, and what it probably won’t do.
  • The longer into the future a forecast is made, the less certain you can be about what will happen.
  • We can expect extreme events – such as abnormally hot seasons and storms, to become more frequent in a warmer world.

The animations were originally developed by climateprediction.net and The University of Oxford Department for Continuing Education (Technology Assisted Life-long Learning Unit).

Categories
Extreme weather Snow

Will it snow?

The best way to find out is to look at the weather forecast charts (in the charts and data menu) at http://www.netweather.tv/index.cgi?action=nwdc;sess= and select ‘HGT 500-1000’ from the ‘select chart type’ menu If the 528dam line is South of where you are, and there is a forecast of precipitation, then that precipitation is likely to be snow.

will it snow isobars
Image of the UK, 5th December 2012

What is the 528dam line?

528dam = 5280m
It is the vertical distance between the 1000mb height (somewhere near the ground) and the 500mb height (somewhere in the middle of the troposphere). As warm air is less dense than cold air, the smaller this distance, the colder the air is.

It is also worth having a look at a cross section through the atmosphere for example at http://www.wetter3.de/ – select ‘Vertikalschnitte’ which gives a longtitude/ height cross section for 50N (move the pointer on the right side of the left hand map to change the latitude of the cross section). The air between the clouds and the ground has to be cold for snow to reach the ground.

When do we get snow in the UK?

More information from the Met Office about Snow in the UK and forecasting snow.

A nice explanation of why we had such a different November in 2011 to the weather in November 2010 from the Met Office and a report on the 2010 snow and its impacts on the UK.

And an article written about some of the work experience students we have had at the Society about whether or not we’ll have a White Christmas with more from the BBC.

Snow inspired science teaching ideas from Science in School.

When will it snow – an article from theWeatherClub

Snow inspired geography teaching ideas from the GA.

How to make a snowflake, from the Institute of Physics

From Brilliant Maps; the probability of a white Christmas across Europe.

Categories
Extreme weather

New Tropical Cyclone Challenge

Use our new online interactive Tropical Cyclone Challenge to discover the recipe for a Tropical Cyclone!

Categories
Extreme weather

Twin Tropical Cyclones in the Indian Ocean

There are two tropical cyclones currently active in the Indian Ocean – one each side of the Equator, and therefore spinning in opposite directions.

You can follow their development on nullschool (which will also let you look back if you missed them), or read more about them at severe weather Europe.
For more on the Coriolis Effect, and why the storms are spinning in opposite directions, have a look at our YouTube video.

https://www.youtube.com/watch?v=zH4nrgozVGk&list=PLxfRaIHcilDfaZlbI5HGNYX1zCOhoKpSq&index=3

For resources designed for teaching about tropical cyclones, covering the processes, hazards, impacts and responses associated with the development of Tropical Cyclones look here. Aimed at KS3 (11-14) and including lesson, homework and assessment resources, the flexible scheme of work uses contemporary case studies

Categories
Extreme weather

Tropical Cyclone Teaching Resources for KS3 (age 11-14)

dorianAs Hurricane Dorian continues to leave a trail of destruction, our new Tropical Cyclones Scheme of Work, covering the processes, hazards, impacts and responses associated with the development of Tropical Cyclones is particularly timely. Aimed at KS3 (11-14) and including lesson, homework and assessment resources, the flexible scheme of work uses contemporary case studies.

Tropical Cyclones Scheme of Work

Categories
Extreme weather Snow

Will it snow?

As the weather gets colder and Christmas approaches, the question of whether or not it will snow, and whether we’ll get a white Christmas becomes important – and a great way to revise some weather processes.

Image courtesy of the Dundee Satellite Receiving Station

Have a look at our resource investigating what weather conditions are required for snow, with some ideas for classroom activities Will it Snow?. You may also like to read the Dreaming of a White Christmas article on theWeather Club site.

 

Categories
Extreme weather Wind

Ophelia: teaching resources

We’ve pulled together some resources about ex-hurricane Ophelia, bringing together information about tropical cyclones, depressions, anticyclones and air masses to explore the extremely unusual weather we experienced in mid-October.

Ophelia PowerPoint

Further information is available in this article from Geography Review.

Categories
Extreme weather

Blown away: the physical facts of hurricanes Harvey and Irma

Philip Monk, a teacher who has worked with the Society on a few projects, has written this useful and timely summary of hurricanes Harvey and Irma for the Geographical Association’s Teaching Geography magazine, which they have kindly let us reproduce here.

Read the article here.

Categories
Extreme weather

The weather of 2013/ 2014

The Geographical Association have put together a useful set of background information and teaching resources focussing on the storms of 2013/ 2014. You can find them at http://geography.org.uk/resources/2014ukfloods/