Weather is what you get, climate is what you expect.
Before we can talk about climate change, it’s important to understand the differences between weather and climate. In the cartoon (right), the first two sentences describe the weather, that is, the short-term changesin the atmosphere. How cold it will be, how many inches of snow the storm will bring, whether there is a frost or freeze warning tonight are all weather-related conversations. Weather is measured in minutes to days, using words like temperature, humidity, precipitation, and wind. The weather forecast helps us figure out what to wear to school, whether to carry an umbrella, and what kind of plans to make for the weekend.
In contrast, climate describes the long-term trends or averages in weather conditions for a particular place. Questions like, whether 16” of snow is normal in April, or are trees budding earlier than usual, or is it hotter than average in July are climate-related questions. Climate is measured over tens, hundreds, or even thousands of years and can be analyzed at local to global scales.
Weather forecasts predict short-term changes in the atmosphere.
Scientists use climate data to study how average temperatures and other weather patterns, such as precipitation and storm frequency will change over time. Compared to the daily or weekly weather forecast, longer-term climate projections help people, towns, and countries plan for and respond to extreme storms and climate change.
Climate projections describe longer-term changes or averages in weather conditions.
The 3-Month Temperature Outlook chart illustrates an example of a short-term climate projection prepared by NOAA’s National Weather Service for Philadelphia International Airport. The graph shows the average temperature range that could occur during each three-month period, based on the median (the middle value in the list of recorded temperatures/mouse over definition) temperatures recorded during the past 30 years (1981-2010). For example, in Nov-Dec-Jan (NDJ) data points, the historical median for that three-month period is 39.6°F, but the average temperature could range from 32.9 to 46.3°F.
Regional Changes in US Precipitation. Source: National Climate Assessment 2014 (updated from Kunkel et al, 2013)
On the right, you can see an example of how long-term climate data can be used to study changes in extreme precipitation events. The average number of extreme rainfall events has been calculated by region for each decade since the early 1900’s. While regional trends show a lot of natural variation, the Northeast and Midwest regions of the country are clearly experiencing increases in extreme rainfall events. Scientists can use this type of climate data to predict the frequency of extreme rainfall events and help guide planners and policymakers in their response to these hazardous events.