Reconstructing Earth’s past climate

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Our climate is changing on a scale that is global and the time frame long. These changes may be imperceptible on a day to day basis, but by understanding what the weather was like hundreds, thousands, even hundreds of thousands of years ago, we can truly see how much has changed. 

“You have to know the past to understand the present.” 

Carl sagan

Unfortunately, Earth’s past climate hasn’t been written down over millennia in one easy to study book. But by utilizing a variety of methods, climatologists can reconstruct what our weather was like over millennia. Melissa Griffin, Assistant State Climatologist for South Carolina, explains,

“The first dataset we use is direct measurements so those are going to be land based stations, buoys, and to a degree satellites, are going to be a direct measurement.”

Temperature, precipitation, humidity, winds, sea surface temperatures- all measured directly using precise instruments. “(The instrumental record) is a very young data record if you look at it as a whole.”

Earth’s instrumental temperature record, which extends into the 1800s.
Credit: NOAA

Young in terms of Earth’s lifetime, but far exceeding our own!

Widespread weather reporting in the US started in the early 1800s, while some informal direct observations are even older. In fact, Charleston is one of the oldest weather recording sites in the nation thanks to a physician who started taking readings of temperature and rainfall back in 1738.

However, our global temperature record extends much further than the 18th century- as Mother Nature records the weather herself.

The tree rings you studied, or as you put it, the amateur dendrochronology… you were able to line up the really good growth years with the really bad years. So you don’t have a direct measurement, that’s kind of an example of an indirect measurement,” says Griffin.

“Some of the other indirect measurements or proxy data would be the amount of oxygen that’s stored in an ice core which would show the amount of warming in the atmosphere. Another example would be taking a core of sediment from a lake bed or deep ocean and looking at the different structure, composition, you can look at fossils, corrals trapped inside of that. That can give you ideas of the changes that you see in the climate cycle without having that direct measurement.”

Using these various climate proxies, paleoclimatologists have been able to reconstruct a fairly consistent and accurate story of Earth’s climate for the past few thousand years- converging with the direct instrumental record in the 1800s. 

Different reconstructions of global temperatures going back 2000 years. Other research, using the geologic record, has estimated Earth’s climate back millions of years.
Credit: NOAA

There’s invaluable data in this temperature record for climatologists to better understand what a future with a warmer climate may look like. It also generates questions such as, “ Hasn’t our planet warmed before?”

That’s a discussion for another time.  

Storm Team 2 Meteorologist David Dickson

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