There is a major difference in the forecasting of daily weather occurrences, and the prediction of a given region’s climate.

Climate describes what the average of weather will be in a specific area or region over a long period of time, usually over a period of 30-35 years. It includes not just the average weather, but also its variability and extremes, as these can have big impacts on the average. Climate encompasses the average measurements of a variety of meteorological factors, such as humidity, atmospheric pressure, wind and rainfall amounts, in addition to temperature. Earth's climate is an entire system, which in addition to the atmosphere, also encompasses its oceans, land masses, topography, the cryosphere and biosphere. All these affect the climate system with their ability to influence long-range weather patterns. Ice for example, is significant to climate because it is reflective, and with current glacial ice measurements covering around 10% of the Earth's surface, it is important in its ability to reflect the sun’s rays back into space.

In contrast, weather is only concerned with short-term events. In most places, weather can change from minute-to-minute, hour-to-hour, day-to-day, and season-to-season. An easy way to remember the difference is that climate is what you expect, like a very hot summer, and weather is what you get, like a hot day with localized storms.

Often, weather experienced in one region (particularly extreme or unusual weather) leads to a somewhat skewed local opinion as to the state of the world’s weather, since people tend to experience their own local conditions and find it hard to envisage differing types of weather being experienced over the rest of the world at that same time.

Climate change refers to a significant change in climate (either global or regional) that lasts several decades or longer. This change may happen for several reasons: it could be due to purely natural changes in the climate system, it could arise from natural factors outside the climate system (for example volcanic eruptions temporarily ejecting aerosols into the atmosphere, or changes in radiation from the sun) or it could be a result of human activity. Although the earth’s climate has changed considerably in the past (and will do so in the future) because of natural factors, it is very likely that most of the global temperature rise observed since the middle of the last century, has been caused by a range of human activities.

This series of short papers is aimed at a general audience with some basic meteorological knowledge and interest. They summarize the science behind the most current topics of interest related to climate and climate change. Questions or comments can be forwarded to me at agajdecki@ametsoc.org.