Qu'est-ce que le climat ?

Latitude determines the angle at which solar radiation reaches Earth's surface. Near the equator, the sun's energy is most direct, absorbing more solar radiation and increasing annual temperatures and rainfall. At the poles, solar rays arrive at a glancing angle, spreading over a larger area and absorbing significantly less energy, resulting in much colder temperatures.

Terrain and bodies of water significantly influence local climate conditions. Mountains can block moisture movement, creating rain shadows with arid climates, as seen with the Andes Mountains and the Atacama Desert in South America. Proximity to water bodies moderates temperature and affects precipitation patterns in surrounding regions.

As Earth rotates on its tilted axis, the amount of solar radiation reaching different latitudes changes throughout the year. This cyclical variation in solar energy distribution creates seasonal temperature and rainfall patterns. The tilt ensures that different hemispheres receive varying amounts of direct solar radiation at different times of year.

Weather describes atmospheric conditions at a specific time and place, while climate represents average weather conditions over extended periods of years, decades, or millennia. Weather forecasts are limited to days, but climate can be modeled and predicted over substantial periods. Climate is what you expect; weather is what you get.

Earth's temperature depends on the balance between absorbed and lost energy. The surface absorbs approximately 49% of solar radiation, while the atmosphere absorbs about 20%. This absorbed radiation warms the planet, which then radiates energy back into space. The ultimate planetary temperature results from this equilibrium between incoming and outgoing energy.

Climate change affects crop yields and food security across regions. Models predict that South Asia and Southern Africa face negative impacts on crops critical to food-insecure populations. Agriculture and food production industries are particularly vulnerable because climate variations directly influence crop growth, water availability, and seasonal patterns essential for farming.

Earth's climate system consists of five interacting subsystems: the atmosphere (gases surrounding Earth), hydrosphere (all water), cryosphere (ice and snow), geosphere or lithosphere (Earth's crust), and biosphere (all ecosystems and living organisms). These subsystems exchange energy, water, and momentum, powered by solar radiation driving all complex climate interactions.