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The Climate of the UK WHAT IS CLIMATE? Some say that climate is what you want, but weather is what you get! If you go on holiday to Majorca in August, you expect it to be hot and sunny – that’s climate. If it rains, you’ve got weather. WEATHER & CLIMATE Weather is the short-term day-to-day state of the atmosphere. It relates to changes in conditions such as temperature, wind and sunshine. Climate is the average of those weather conditions, measured over thirty years. MILD AND WET The UK’s climate is generally mild and wet. They generally have a temperate maritime climate, which is influenced by the sea surrounding the UK. In summer the sea cools the climate, and in winter the sea insulates the UK – keeping it warmer than other places at the same latitude. However, the UK’s climate is not the same everywhere! EXPLAINING CLIMATE Why is the UK’s climate mild and wet? There are a number of factors that help to explain it, but the most important one is latitude. The further you go from the equator, the cooler it gets. Why? Because the Earth’s surface is curved, which means that the sun’s energy isn’t evenly distributed. LATITUDE The diagram shows how the sun’s energy is much more direct and concentrated than at the Poles. This means that the earth is hottest here. At the North and South Poles, the greater curvature of the Earth. means that the sun’s energy is spread over a larger area. This means colder temperatures. Ice forms there and reflects heat back into space, making it even colder. DISTANCE FROM THE SEA The sea is cooler than the land in summer – but warmer in winter – because it takes longer to heat up than the land, but is slower to cool down. The sea moderates the UK’s climate, making temperatures more even throughout the year. The interior of countries with large land masses, like the USA, have a continental climate. It is too far from the sea to be influenced by it, and so they have very cold snowy winters, and hot dry summers. Ocean Currents The North Atlantic Drift is a current of warm water that flows across the Atlantic from the Gulf of Mexico. It keeps the coasts of western UK much warmer than areas inland. ALTITUDE Temperature decreases by 1°C for every 100m of altitude (height above sea level [ASL]). So, mountainous areas are always cooler. These also tend to get more rain (because of relief rainfall), so they are wetter too. Prevailing Winds A prevailing wind is the direction from which the wind blows most often. The prevailing winds for Europe are from the south-west. The temperature of a prevailing wind is affected by the area it blows over Theses winds bring more rain to western parts of UK. WET, WET, WET It’s always raining in the UK – or at least that’s how it feels. In the UK we get 3 types of rainfall: relief rainfall (sometimes called orographic) convectional rainfall frontal rainfall (we will learn about this next lesson) RELIEF RAINFALL Warm moist air arrives from the Atlantic Ocean and rises over the mountains on the western side of Britain – the Cambrians, Pennines and Grampians. When it rises, it cools, condenses into a cloud and starts raining. The mountain peaks can receive a lot of rain – up to 2000 mm a year. Once the air has passed over the mountains, it descends and gradually warms as it reaches lower ground. This creates drier conditions and is called the rain shadow. Therefore, mountains in the UK tend to be wetter in their windward, western sides and drier on their leeward, eastern sides. RELIEF RAINFALL RELIEF RAINFALL CONVECTIONAL RAINFALL During the summer, strong sunshine causes the ground to heat up rapidly. This sets up rising pockets of warm air, known as convection currents. The warm air rises rapidly to a high altitude, where it cools and its water vapour condenses to form clouds. With time, particularly late afternoon, thick cumulonimbus clouds can form. These can produce heavy rainfall and sometimes thunderstorms. Therefore, some places like Cambridge have their wettest months in July or August. CONVECTIONAL RAINFALL PRESSURE AND WINDS Around the world some areas have high pressure and some have low pressure. 1. The UK is in a low-pressure zone. Air is rising here. 2. Air cools, condenses and forms clouds – then it rains and the UK gets its wet weather. QUESTIONS 1. Explain how latitude affects the climate of the UK. 2. Explain how distance from the sea affects the climate of the UK.