Understanding weather and climate

 

The difference between weather and climate is simply time. Climate tells us what the weather is usually like, for example summers are usually hot, and weather is what you get at a particular place and time, for example a hot day with a sudden thunderstorm. When we talk about climate change, we talk about changes in the long-term averages of daily weather.

Just as the weather changes from day-to-day, climate also changes. Global and regional climates are in a constant state of change on time-scales from months to millions of years.

The earth’s climate has seen periods of intense warmth and bitter cold. These historical changes in the climate were caused by natural processes, but there is increasing evidence that human activities have the potential to cause additional changes to the climate.

Natural causes of climate change include changes in the earth’s orbit, the sun’s activity and ocean currents, large volcanic eruptions and meteor impacts. Oceanic and solar influences have a mild to strong influence on year-to-year climate variability. Periods of warming and cooling in history can be attributed to these types of events.

Human activity is also contributing to longer-term climate variability, through increases in the concentrations of some greenhouse gases in the atmosphere. Since the industrial revolution there has been a steep rise in the concentration of greenhouse gases in the atmosphere.

Greenhouse gases include carbon dioxide, methane, nitrous oxide and water vapour. They capture the heat that is given off when the sun’s energy warms the surface of the earth. This direct human contribution to an increase in greenhouse gas concentrations is often referred to as the enhanced greenhouse effect. Contributing activities include burning of fossil fuels, deforestation, farming and landfill sites.