How a past climate may be determined

Practically on a daily basis, we’re hearing about climate change and weather extremes. Climate scientists are constantly working on new models and methods to get more insights into our planet’s climatological future. Recently, I completed a fascinating course on past climates and in an upcoming series of articles, I will highlight what methods are used to construct past climates, some of the theories of those changes and what periods of ancient times may be indicators of what our future climate may look like.

To understand current and potential conditions, the examination of past climates, which is called paleoclimatology, is crucial for comprehending current and future trends. Paleoclimatologists will use various methods and models to reconstruct past climate conditions. They will use different sources of evidence that span geological, biological and chemical records. These methods include the study of ice cores, tree rings, sediment cores and fossils that often provide unique insights into historical climate patterns.

The examination of ice cores is one of the most widely used indicators of past climates. Scientists will drill cylindrical samples from large ice sheets and glaciers, mainly from Antarctica and Greenland. The longest records are from Antarctica that date back to around 800,000 years ago. Some of the ice core drilling can reach depths of over 2 miles. In Greenland, ice cores have climate records dating back about 115,000 years, so the information is not as extensive when compared to Antarctica.

Paleoclimatologists will analyze each thin layer of ice to determine each year’s snowfall. The ice samples will also trap dust, gas concentrations of carbon dioxide, methane and others to construct past atmospheric compositions and temperatures in that location.

The study of tree ring data, also known as dendrochronology, has become very important in determining a region’s past climate. Trees are sensitive to the area’s local conditions and each year, the tree will grow rings, which also provides an age for the tree. Depending on the weather patterns during a particular year, a tree ring can give scientists a good idea of the local climate. For example, during warm and wet seasons, the tree rings are usually wider, but they are thinner when it’s usually cold and dry. If there are drought conditions, there may be limited growth. Researchers can build a continuous climate timeline by using cross-dating techniques to match ring patterns between different trees.

Many trees can live for hundreds and even thousands of years. One of the oldest living trees in the world, according to nasa.climate.gov, is the Methuselah Tree in White Mountain, Calif. It’s estimated that the bristlecone pine tree is almost 5,000 years old.

Other past climate indicators will include sediment cores from lakes, oceans and other bodies of water. Like ice cores, these sediment layers accumulate over time and will represent specific historical periods.

Some of the sediments will include grains of pollen and by identifying the different types, scientists can determine the type of vegetation that existed, including the changes over time.

Fossils will also be preserved in the sediments and the examination of fossilized organisms will indicate past water temperatures and salinity levels. The distribution of fossilized plants and animals from sediment cores can provide insights and trends of past climates as they can provide an indication of past temperature, precipitation and atmospheric composition over very long periods of time.

There are other climate indicators that are studied including corals, which are sensitive to ocean temperature changes. Because temperature and rainfall vary together in the tropical Pacific Ocean during El Niño and La Niña events, examination of ancient corals can be a very good indicator.

Another past climate indicator that is being further studied is the study of speleothems. Many people may have seen these features in underground limestone caves that have small to large cone-shaped objects from the ceiling to the floor. These are mineral deposits formed from groundwater within the caves and can be dated. The thickness of these layers within the speleothems can be used to determine the area’s past climate conditions over thousands of years.

I’ll have more information on long-term climate trends and theories in future articles. As far as our local weather is concerned, July’s weather will certainly be one of the hottest and driest in recorded history in Coeur d’Alene and surrounding regions. Unless there is some rainfall by Wednesday, July of 2024 many stations will end up with no measurable moisture for the month.

With the dry and hot weather across the West, according to the National Interagency Fire Center, there are nearly 100 fires burning across the western portions of the country as well as Canada. Many have been started from dry lightning. As of the weekend, there are nine major fires in Washington, 10 in Idaho, 14 in California and a whopping 37 in Oregon. Some of these blazes, especially in California, have prompted evacuations and air quality alerts.

More very hot weather is expected late this week as high temperatures will once again be near or over the 100-degree mark. The hot and dry conditions are expected to continue into next week, but the long-range computer models are indicating an increasing chance of rain and cooler temperatures by the weekend of Aug. 10.

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Contact Randy Mann at randy@longrangeweather.com.