When scientists focus on climate from before the past 100-150 years, they use records from physical, chemical and biological materials preserved within the geologic record. Organisms (such as diatoms, forams and coral) can serve as useful climate proxies. Other proxies include ice cores, tree rings, and sediment cores.

Definition. Atmospheric science is the study of the dynamics and chemistry of the layers of gas that surround the Earth, other planets and moons. This encompasses the interactions between various parts of the atmosphere as well as interactions with the oceans and freshwater systems, the biosphere and human activities.

A climatologist studies weather patterns over a period of time.

Scientists who specialize in this field are called climatologists. By studying global warming, climatologists can better understand and predict the long-term impact of human-caused climate change. Climatologists seek to understand three main aspects of climate.

Guy Callendar

It’s important that we understand how the climate is changing, so that we can prepare for the future. Studying the climate helps us predict how much rain the next winter might bring, or how far sea levels will rise due to warmer sea temperatures.

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Physical proxies include characteristics such as sediment composition, texture, structure, color, density, and magnetic properties, among others. Scientists use changes in physical properties of archive materials to infer past climate conditions.

Clues about the past climate are buried in sediments at the bottom of the oceans, locked away in coral reefs, frozen in glaciers and ice caps, and preserved in the rings of trees. Each of these natural recorders provides scientists with information about temperature, precipitation, and more.

In the study of past climates (“paleoclimatology”), climate proxies are preserved physical characteristics of the past that stand in for direct meteorological measurements and enable scientists to reconstruct the climatic conditions over a longer fraction of the Earth’s history.

When the carbon dioxide concentration goes up, temperature goes up. When the carbon dioxide concentration goes down, temperature goes down.

These proxy data are preserved physical characteristics of the environment that can stand in for direct measurements. Paleoclimatologists gather proxy data from natural recorders of climate variability such as tree rings, ice cores, fossil pollen, ocean sediments, corals and historical data.

The light and dark rings of a tree. These rings can tell us how old the tree is, and what the weather was like during each year of the tree’s life. The light-colored rings represent wood that grew in the spring and early summer, while the dark rings represent wood that grew in the late summer and fall.

A tree’s growth rate changes in a predictable pattern throughout the year in response to seasonal climate changes, resulting in visible growth rings. Each ring marks a complete cycle of seasons, or one year, in the tree’s life.

The girth of a tree can be used to estimate its age, as roughly a tree will increase it’s girth by 2.5cm in a year. So, simply measure around the trunk of the tree (the girth) at about 1m from the ground. Make sure you measure to the nearest centimetre. Then divide the girth by 2.5 to give an age in years.

Occasionally, trees will produce more than one ring in a year. The extra ring is called a false ring and it can be the result of drought stress in the middle of a growing season. Other times a tree can go a year without producing a ring.

Andrew. E. Douglass

Climate scientists compare the tree growth records to local weather records. For locations where a good statistical match exists between tree growth and temperature or precipitation during the period of overlap, the ring widths can be used to estimate past temperature or precipitation over the lifetime of the tree.

Maximum Latewood Density (MXD): A parameter that measures peak density of the latewood cells in a given tree ring (Schweingruber, 1988). MXD is sensitive to warm season temperatures and is complementary to ring width.

The study of the growth of tree rings is known as dendrochronology. The study of the relationship between climate and tree growth in an effort to reconstruct past climates is known as dendroclimatology.