extreme events
Conservation of Energy in Systems
The law of conservation states that the total energy of an isolated system remains constant. In other words, the energy in a system cannot be created or destroyed, but it can change forms. This concept is important for understanding how weather becomes extreme as explained below.
Energy in a system cannot be created or destroyed, but what is a system?
Our bodies are systems. Our Universe is a system. A thunder storm is a system. In all of these examples, different things work together to form a whole; in other words, they are a system.
In a system, you’ll often find a number of characteristics such as cause and effect relationships, structure, boundaries, smaller systems, and the flow of energy. Within these systems, energy cannot be created or destroyed, but it can take different forms and pass through boundaries. It is often useful to draw an imaginary boundary around a system so you can easily account for any stuff that enters or leaves the system. By monitoring the amount of energy that enters or leaves the system, we can predict what might happen within the system (e.g., a hurricane or thunderstorm).
What is energy?
Energy is the ability to do work. When something expends energy – a person runs, lightening happens, or a car moves – it is doing work.
There are two main classifications of energy – Kinetic (moving) energy, and potential (stored) energy. A plant growing, a person clapping, and a hurricane forming are all examples of kinetic energy. Examples of potential energy include a pencil sitting on a desk and a spring that has been pushed – both have energy but are not using it.
Within these two classes are many different types of energy such as chemical energy (contained in food, for example), mechanical energy (objects that are moving, like a ball rolling down a hill), electrical energy (electricity we get from a battery, for example), thermal energy (the energy of motion, which we call “temperature”), and sound energy (vibrations in air, water, or some other matter that we can hear with our ears).
Energy can change forms too. For example, the electrical energy in an oven is changed to thermal energy to cook your dinner.
Where does energy in weather come from?
In addition to changing forms, energy can also cross system boundaries, and this helps explain a lot of extreme weather.
The energy in weather can come from many different sources, depending on the type of weather. In a Nor’Easter, the energy can come from the heat of the Gulf Stream and the movement of air in the jet stream. In a heat wave, energy comes from the sun, heat trapped in humidity, and the movement of air and pressure systems. In a thunder storm, energy comes from the sun and from rain, which is energy when it is cooled and condenses.
What happens to the energy in extreme weather?
Often times, the energy that fuels extreme weather exists in forms we can observe. For example, strong winds associated with hurricanes, nor’easters, and tornadoes, lightning, and precipitation are all examples of energy changing form.
Different aspects of weather have different amounts of energy. Energy is sometimes measured in Joules (J) but can also be measured in gallons of gasoline, M&Ms, or sticks of dynamite. On average, the energy of a lightening bolt is similar to the amount of energy in 7.5 gallons of gasoline, while a tornado may contain as much energy as 273 gallons of gasoline!
Some people have thought about ways to use the energy found in weather systems (not just extreme weather) to create electricity that we can use – like in our homes, schools, and places of work. Wind turbines and solar panels are great examples of tools used for that purpose.
Where does energy on Earth come from?
Most of the energy on Earth comes from the sun but there are also geothermal sources. Some of the sun’s energy is absorbed by the surface of the Earth. Clouds and atmospheric gasses and particles reflect a portion of the sun’s energy back into space, and some of the energy is absorbed by clouds and the atmosphere. This idea of where the earth’s energy comes from and how it is absorbed and reflected is the Earth’s Energy Balance. Globally, weather, winds, and ocean circulation are the result of differential heating of the Earth (e.g., more sunlight at the equator than at the poles).