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Weather is local and short-term. If it rains or is sunny in the town where you live tomorrow, that's the weather; but you probably have a very good idea what type of weather to expect for your town in any given January or August, that’s due to its climate.
Climate tells you what clothes to buy and have in your wardrobe, weather tells you what to wear each day.

Weather is a description of conditions over a short period of time - a snap shot of the atmosphere at a particular time.

Weather can be changeable  day-to-day, hour-to-hour and even minute-to-minute. And weather can be very local. (Have you ever stood in the rain and seen somewhere in the distance still bathed in sunlight?)

If you go on holiday the area’s climate tells you what clothes to pack and what weather to expect for that time of year.

Climate tells farmers what crops they can plant and when to plant and harvest them - or if they can grow crops at all. Climate determines the type of vegetation that will grow in a region and the types of wildlife that will survive there.

Climate is the sum of all the weather recorded over a long period of time. A climate is the description of the average seasonal temperatures, atmospheric pressure and the amounts of precipitation, cloud cover, sunlight, wind, humidity etc.

Climate takes into account altitude, latitude, distance from oceans, the direction of prevailing winds and so on and is usually measured over periods of 30 years or so. The climate of an area or region is the average pattern of weather conditions in a region over a long period of time. So climate is about long-term records, averages and trends.

Climate is what the weather is normally like year to year, decade to decade, even taking into account exceptional blizzards, floods or heat-waves. Climate looks at a number of years, not just one year; weather is the month-to-month, day-to-day variety experienced within that region's climate. See below.

Weather is caused by disturbances within the atmosphere, mostly in the lowest 10-15 kilometres of it; but climate is controlled by external influences, such as latitude, the distribution of oceans and continents, the position of mountain ranges, the distribution of ice and snow-cover, variations in the amount of energy emitted by the sun, changes in the chemical composition of the atmosphere and changes in land-use to mention but some. In earth's deep past major variations in greenhouse gasses have also caused considerable changes to climate.

Climate Zones
We know there are many different climate zones in the world that share common characteristics. These can be characterised by the type of vegetation they support as well as by temperature, seasonal characteristics, precipitation and the like. Many types of plants only thrive in particular conditions. (We also know why there are seasons - due to the earth’s spin and the angle of its axis, not its distance from the sun - and why between the tropics of Cancer and Capricorn there are only two seasons a year; wet and dry.) A region’s weather also changes according to the time of year, the seasons and, less often, because of naturally occurring phenomena such as El Nino/La Nina events, changes to the paths of the jet streams and the like.

You will probably recognise these (general) terms often used to describe various climate zones: (Other terms used for these are given alongside.)
Polar – (or: Arctic.) –  North & South Poles. Very cold and mainly dry all year, temperatures only reach above freezing for around a third of a year.
Sub-arctic (or: Northern Temperate, Boreal, Taiga.) –  Long, very cold winter with much snow, short mild summer; supports coniferous forest.
Temperate – Cold winters and mild summers; supports deciduous forest.
Continental (or: Temperate grassland) – The Prairies,  Pampas etc. Often the interior of a continent far from the oceans.
Mediterranean - Mild winters, hot, dry summers.
Semi-Arid – Semi-arid climates usually have scrub or grass vegetation and often border true deserts. Also known as Steppe climate.
Arid – Deserts. Generally dry all year round, little precipitation, clear skies. Big daily temperature range between day and night.
Savannah (or: Tropical grassland.) –  Has a long dry season and a short wet season, but with heavy rainfall.
Sub-Tropical – A dry season followed by a wet (monsoon) season. Within sub-tropical zones you can find both cloud forests and monsoon forests which have a long dry-season followed by a season of heavy rainfall; the vegetation is adapted to withstand drought and trees are semi-deciduous or evergreen.
Tropical – Generally constant warmth, receives both much sunlight and rainfall. Likely to hold tropical rain forest - with year-round rainfall and warmth.

Within broad climatic zones we can also identify smaller varieties of climate; but which still cover quite large areas, these are known as Macroclimates. e.g. The western coastal areas of Europe have a milder climate than Central Europe (Water holds heat longer than land; because it releases this much more slowly, land close to a sea is warmed by it even in winter.) and the Mediterranean climate of California.

Mesoclimates. These are smaller areas than macroclimates. e.g. areas that may only cover a few square kilometres, but can be larger. An example is the Napa Valley region of California. A smaller example would occur in mountain areas; the side of a mountain that receives most sunlight and is sheltered from prevailing winds has a different climate from the opposite side that is colder and more windswept. In coastal areas or islands the clash of differing land and sea temperatures can produce very localised effects such as thick fogs. (There are various types of coastal climate zones.) You will notice in hilly landscapes that most varieties of plant life are found down in the sheltered valleys. In mountain areas there are three main mountainous climatic zones: alpine, subalpine or montane, depending upon altitude.  Cities also can generate their own climates.

And you can find small Microclimates that refer to a very specific local area. e.g. On a mountainside a gully can be darker, wetter and more sheltered than the rest of the cliff, supporting very different vegetation to the surrounding area. And as gardeners know, north and south facing gardens, on the opposite sides of a house, may be better suited for different types of plants, they each have a microclimate.

Meteorologists now understand many of the factors that determine the climate of a region e.g. its latitude, altitude, its distance from an ocean, the direction of prevailing winds, ocean currents and so on. For example, Oslo in Norway is approximately on the same latitude as the southern tip of Greenland, but has a considerably more temperate climate. There is a reason for that - Oslo has a warmer climate because of an ocean current, the Gulf Stream, that carries warmer waters across the Atlantic ocean towards Scandinavia. They also know the causes of regular regional seasonal winds such as the Chinook, Föhn, Mistral and Shamal; when and where to expect monsoon seasons and where and when in the world to expect hurricanes, typhoons or cyclones and why these occur and much more.

Understanding the earth’s climate system is understanding the processes that cause air or ocean currents to circulate, why winds form, how heat from the sun causes moisture to become part of the atmosphere, why warm air rises and cool air sinks (this also causes winds), why when the air cools the vapour condenses and falls as precipitation and much, much more.

Predicting Changes To Climate
In many ways predicting any changes to a climate can be easier than predicting the weather, providing we can discern a noticeable trend, changes to a climate over a long period of time. Trends tell us what the likely future climate of that area is likely to be (we also have a historical record to compare periods with and helps us recognise when a region’s climate zone changes).

Flora and fauna are often quite sensitive to changes in climate and may expand their range or die off, depending if changes favour them or not.

For example, tropical savannahs are a transitional stage between an arid climate and those of a tropical rainforest. If a savannah receives less and less rainfall then vegetation suffers and it begins to take on the characteristics of an arid area. When its rainfall, over a period of years, matches the amount found in an arid area then the vegetation and landscape will also begin to match those already found in an arid area. If it receives more rainfall than usual over a period of years then vegetation from neighbouring rainforest will take the opportunity to expand and colonise the grassland which is now more able to support forest.

Given it is possible to detect changes to climate we then have to look at the likely causes to try and determine how long and severe they will be, at how any changes will effect other climate mechanisms and what the impacts of those will be? From the trends it's possible to see what  the likely impacts will be and attempt to plan for them. Areas, for example, likely to suffer increased drought - or increases in incidence of flooding.

A few related Weblinks:
Basic introduction to how planet earth works, including atmosphere, climate zones etc.
Good list of education websites to do with forecasting and climate.
Another good list of education websites to do with forecasting and climate.
USA Today has an interesting page about understanding weather forecasting techniques.
The BBC website weather section's page on processes that produce certain types of weather.
An Introduction to the Global Climate System.
How birds can signal a change in climate.

2008