People often ask, “What is the difference between climate and weather?” Although climate and weather are closely related, there are some important differences. The simple explanation defines weather as what you get today and climate as what you get over the long-term (typically 30 years or more).
An analogy may help to explain. Most of us have heard of the famous baseball player Babe Ruth. He hit a high percentage of home runs over his career. But when he stepped up to the batter’s box in a game, you didn’t know if he would hit a home run or strike out (for which he was also famous). What happens at that individual “at bat” is weather. The statistics of home runs and strike outs over his career are climate.
If you are too young to remember Babe Ruth, here is another example. Imagine a woman walking her dog on the beach. As they pass by, you can see their tracks in the sand. The woman’s tracks are in a straight line. But the dog’s tracks show an erratic pattern. Depending on the length of the dog’s leash, the dog’s tracks show a pattern of darting back and forth over the woman’s track as it investigates various spots on the beach. The dogs tracks are weather and the woman’s tracks are climate.
If the woman changes direction, the dog’s tracks will also change in that direction. Just like a warmer climate will cause more record high temperatures than record low temperatures. For example, although 2017 ended with a cold spell in the U.S., over the entire year there have been three record high temperatures for every record low.
The variability of weather over time is also evident over geography. Although we suffered from a recent cold spell, the U.S. only makes up two percent of the Earth’s surface. The temperature over the rest of the world can easily more than offset the temperature in the U.S. During the U.S. cold spell, temperatures in much of the rest of the world were above average.
The climate can be tipped in a different direction, often by relatively small external influences. Returning to Babe Ruth, a bit of arthritis in an elbow or a small change in eyesight can greatly impact his batting average.
You may ask, “If scientists have difficulty predicting tomorrow’s weather, how can they predict climate far in the future?" Weather is short term and chaotic, and is determined by current atmospheric systems that may soon be replaced by other systems. So, it is difficult to predict weather more than a few days in advance.
Conversely, climate is the average weather over a long period of time, typically 30 years or more. It is determined by large-scale forces like the level of greenhouse gases in the atmosphere. So it is easier to predict long-term changes in climate than short-term changes in weather.