Stories in Ice

Have you ever wondered how scientists know what earth's climate was like, hundreds or thousands of years ago? After all, they weren't there to observe and record changes. Just like detectives, scientists can reconstruct the climate story by looking for clues and evidence that can help tell them about the past. In some cases, scientists can use ice cores, samples taken from glaciers to help them get an idea of what the climate was like in an area. But what about the ice? Tell scientists what the climate was like so many years ago. What are the important characteristics of climate? It's important to understand the difference between weather and climate. Weather is the day to today changes that we see. Climate is the overall average that occurs in an area over years. Hundreds of years or thousands of years. So climate describes what it's like in a certain place over a long period of time. Things like temperature, precipitation, windiness, cloudiness, and the amount of certain gases found in the atmosphere are important characteristics used to describe climate. How do scientists study climates from hundreds or thousands of years ago? This is where ice cores come in. Scientists can study things that are preserved in the ice in order to piece together the story of how climate has changed over the years. How are stories preserved in ice? To get an idea of what the climate was like, many, many years ago. Scientists use what are called proxies. Proxies are indicators. Things that scientists can study within in this case, the ice cores that help them describe what the climate was like and has been like so many years ago. So, if we think of an ice core as a mystery book, scientists are the detectives looking for the clues in the layers of ice that can help them solve the mystery of earth's climate history. Scientists look for things like dust, pollen, or volcanic ash that are trapped within the ice to help them understand past climates. These things are called proxies, climate scientists use proxies as substitutes for actual observation of conditions, such as temperature, wind, and rainfall. Let's see if you can use your detective skills to solve this proxy case. Imagine that you're given the assignment to describe what the weather is like outside over a period of one month. The problem is that you are stuck in the school coat closet. You do not have access to the outside world, and you can't talk to your classmates. The only information that you have is the items that your classmates are putting into the closet with you each day. Do you think you would get an idea of what the weather is like outside? Items like sunglasses, rain boots, and umbrellas are your proxies. They're indicators that can help you know what the weather is like outside. Let's look at a real example of a proxy from an ice core and see how scientists describe the amount of precipitation in a certain location. Places around the world usually have a wet and a dry season. During the wet season, a layer of snow is laid down on top of the glaciers. During the dry season, not as much snow is laid down, and there's more dust in the air. So what happens is we get this pattern that can be clearly seen of a wet and a dry season. Together, this wet and dry season equals the amount of precipitation in one year. The thickness of that layer can help scientists tell how much precipitation there was in that location. When scientists compare this proxy for precipitation, to other proxies found within the layers of the ice, like volcanic ash, dust, and pollen. They can peach together a more accurate story of what happened in the past. Scientists also examine oxygen atoms of two different weights that are found within the ice to get an idea of what the temperature was like. They also study the air bubbles that are trapped within the ice, these are small samples of what the atmosphere used to be like when that snow fell. Within every layer of ice core, there is a story to investigate. So proxies are the clues found in the ice cores that scientists use to piece together the story of how earth's climate has changed over so many years.