- The global climate system is made up of 5 parts: the atmosphere, lithosphere, hydrosphere, cryosphere and biosphere.
- Global climate is influenced by many factors, including the sun, Earth’s position in space relative to the sun, and human-made factors such as greenhouse gas emissions.
- Today’s global climate is warming rapidly due to human activities that increase greenhouse gas emissions.
What is the difference between weather and climate?
Weather can be thought of as short-term changes (over hours or days) and climate as long-term changes (over years or even thousands of years).
Weather includes factors such as temperature, wind, rain, clouds, atmospheric pressure and humidity. These are observed or predicted over smaller regions. Weather is influenced by the global climate system.
Climate is defined by long-term weather averages, variations and extremes. Local climates are influenced by their distance from the equator, elevation, distance from water bodies, vegetation, the presence or absence of mountains, and other geographical features. Climate also varies over time through seasons, years, decades and much longer timescales such as the Ice Ages.
The global climate system
The global climate system arises from the interaction of 5 systems interacting together. To understand our climate and how it is changing, we first need to understand these 5 systems:
- The atmosphere (the thin layer of gases surrounding the earth)
- The lithosphere (the land surfaces such as soil and rocks, and human-made surfaces such as roads and buildings)
- The hydrosphere (the Earth’s liquid water in oceans, rivers, lakes and underground)
- The cryosphere (the frozen water in ice and snow)
- The biosphere (the living things such as plants and animals including humans).
The atmosphere is the thin layer of gases surrounding the Earth. The atmosphere is important for regulating the Earth’s temperature.
The types and amounts of gases in the atmosphere can change how much heat and light can pass through. Some gases can trap heat. These gases are called greenhouse gases and include carbon dioxide and methane.
Human activities such as burning fossil fuels are rapidly increasing the amount of greenhouse gases in the atmosphere. This is causing our climate to warm.
The lithosphere is the land surfaces such as soil and rocks, and human-made surfaces such as roads and buildings. The different materials that make up the lithosphere absorb different amounts of energy from the sun, while mountains can slow or redirect winds and affect where rain falls.
A major natural part of the lithosphere in NSW is the Great Dividing Range. This range influences climate by affecting wind and rain patterns across the state.
The hydrosphere is all of the Earth’s liquid water found in oceans, rivers, lakes and underground. Oceans help regulate Earth’s temperature by absorbing and releasing heat from the sun. This heat is transported around the world through ocean currents like the East Australian Current. This influences the NSW climate.
Water evaporates from oceans and waterbodies and collects as water vapour in the atmosphere. The process of evaporation helps keep climate close to these water bodies cooler and the water vapour can also fall as rain.
Important parts of the hydrosphere in NSW include our oceans, rivers and lakes, which we depend on for recreation and industries. Freshwater from rivers, lakes, rainfall and underground (groundwater) is important for our rich agricultural regions.
The cryosphere is the frozen water in ice and snow. The cryosphere is mostly made up of sea ice in the Arctic and Southern oceans, and the land-based ice sheets of Greenland and Antarctica. It also includes the ice and snow in many elevated regions across the globe.
Ice and snow help regulate climate, as their white colour reflects energy from the sun back into space. The seasonal freezing and melting of snow and ice helps ocean water circulate around the world.
Ice and snow are not common in NSW. Some inland regions with higher elevation, such as the Snowy Mountains, regularly experience snowfall in the cooler months. This affects the climate of surrounding areas, as winds that blow across the snow-covered areas tend to be much colder.
The biosphere refers to the livings things that are found on Earth. Life plays an important role in the Earth's climate over short (seasonal) and long time-scales (millions of years). For example, plants absorb carbon dioxide from the atmosphere which helps regulate the global climate and reduces the rate of global warming.
Under the right conditions and over thousands to millions of years, plants lock away carbon dioxide through the formation of peat and coal.
What drives the world’s climate?
The global climate system is driven mostly by energy from the sun. It is also influenced slightly by the gravitational pull of the moon and heat from the Earth’s core.
The sun provides an almost constant source of energy for Earth. About 30% of this energy is reflected back into space by the atmosphere and some surfaces of the Earth. The remaining 70% of the energy is absorbed, mainly by oceans and gases in the atmosphere, with a small amount being released back into space. Different surfaces, greenhouse gases and airborne particles can all affect how much energy is reflected and absorbed.
If Earth is absorbing and reflecting energy in equal amounts, the Earth’s temperature will remain the same. If more energy is absorbed than reflected, then the Earth begins to warm.
The curved surface of the Earth creates different climates across the globe.
Because of the Earth’s round shape, the equator is the closest point to the sun. It receives most of the sun’s energy and the polar regions receive less. This creates the warm tropical regions and cold polar regions. The extra heat at the equator also drives the movement of air up and away from the equator which creates the circulation patterns that form weather systems.
The energy Earth receives from the sun varies over time for a few reasons. We experience short-term changes in climate every year as the Earth orbits the sun causing the seasons. Long-term changes occur slowly over tens of thousands of years, based on changes to the shape of Earth’s orbit and the position of its axis.
Current global climate trends
The global climate is warming much faster than the natural cycles of the Earth. Today’s rising temperatures are caused by greenhouse gases being produced by human activities.
A process known as climate feedback can amplify small changes and make our climate change even faster. For example, as temperatures rise, snow and ice sheets melt. This uncovers land and water surfaces that then absorb more of the Sun’s energy causing more warming, which causes higher temperatures and more melting in a self-reinforcing cycle.
A tipping point in the climate system occurs when a critical threshold is exceeded that then leads larger and often irreversible change. Some examples include large scale thawing of frozen soils in the arctic (permafrost) and melting of the Greenland and West Antarctic ice sheets.