The difference between weather and climate is time – weather happens daily and climate happens over longer periods.

Weather is the day-to-day state of the atmosphere, and its short-term (minutes to weeks) variation. Popularly, weather is thought of as the combination of temperature, humidity, precipitation, cloudiness, visibility, and wind. We talk about the weather in terms of “What will it be like today?”, “How hot is it right now?”, and “When will that storm hit our section of the country?”

Weather is basically the way the atmosphere is behaving, mainly with respect to its effects upon life and human activities. In most places, weather can change from minute-to-minute, hour-to-hour, day-to-day, and season-to-season. Climate, however, is the average of weather over time and space. 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 pop-up thunderstorms.

Climate is defined as statistical weather information that describes the variation of weather at a given place for a specified interval. In popular usage, it represents the synthesis of weather; more formally it is the weather of a locality averaged over some period (usually 30 years) plus statistics of weather extremes. It is climate at your place on the globe that controls the weather where you live. Climate is the average weather pattern in a place over many years. So, the climate of Antarctica is quite different than the climate of a tropical island.

So in other words, the difference between weather and climate is a measure of time. Weather is the condition of the atmosphere  over a short period of time, and climate is how the atmosphere “behaves” over relatively long periods of time. In other words, climate is what you expect for a given area, and weather is what you get.

In short, climate is the description of the long-term pattern of weather in a particular area.

Some scientists define climate as the average weather for a particular region and time period, usually taken over 30-years. It’s really an average pattern of weather for a particular region.

When scientists talk about climate, they’re looking at averages of precipitation, temperature, humidity, sunshine, wind velocity, phenomena such as fog, frost, and hail storms, and other measures of the weather that occur over a long period in a particular place.

For example, after looking at rain gauge data, lake and reservoir levels, and satellite data, scientists can tell if during a summer, an area was drier than average. If it continues to be drier than normal over the course of many summers, than it would likely indicate a change in the climate.

When we talk about climate change, we talk about changes in long-term averages of daily weather.

Today, children always hear stories from their parents and grandparents about how snow was always piled up to their waists as they trudged off to school. Children today in most areas of the country haven’t experienced those kinds of dreadful snow-packed winters, except for the Northeastern U.S. in January 2005. The change in recent winter snows indicate that the climate has changed since their parents were young.

If summers seem hotter lately, then the recent climate may have changed. In various parts of the world, some people have even noticed that springtime comes earlier now than it did 30 years ago. An earlier springtime is indicative of a possible change in the climate.

IPCC illustration of effects on extreme temperature when (a) the mean increases, leading to more record hot weather, (b) the variance increases, and (c) when both the mean and variance increase, leading to much more record hot weather.

Expected effects of climate change

It is likely that climate change will increase mean temperature in many areas (IPCC). It is also likely that many areas will esperience more climate variability.

The likelihood of more extreme events (particularly drought and heat stress) arises from the distributional impacts of an increase in mean temperature as well as the possible increase in temperature variation (IPCC 2001a).  The effect of global warming on the incidence of extreme heat is illustrated in the figure.

For a normally distributed variable such as temperature, a small increase in its long-term mean, variance or both can produce substantial changes in the probability of occurrence of extreme heat.

For other variables that may not necessarily be well-approximated by normal distributions, like frost or precipitation, the situation is even more complex, especially for dry climates.

For precipitation, changes in the mean total precipitation can be accompanied by other changes like the frequency of precipitation or the shape of the distribution including its variability and therefore the probability of occurrence of precipitation extremes.