Past Climate Change

Has Earth’s climate always been the same?


Earth has experienced climate change in the past; in fact, these changes seem to cycle over thousands of years. Ice ages lasting 12 000 to 60 000 years have alternated with warm periods called interglacial periods. Earth is currently in an interglacial period that started about 11 500 years ago.

We know about past climate change because of evidence left in different parts of Earth, including but not limited to trees, glaciers, oceans, coral reefs, and rocks.

Glacier ice is layered in years.  Air pockets found in different layers of ice give us a climate record that goes back as much as 800 000 years. By taking samples of the air found in  air pockets, we can get a detailed look at what the atmosphere was like during the time that layer was formed. The different particles found in the ice itself give scientists a clue as to the average global temperature at that time.
We think that data from ice cores is reliable because the findings about climate are confirmed by other data sources.  Varves from sedimentary rock deposited on lake bottoms show the same results.

Climate change in the past has been due to small shifts in how the Earth orbits the sun, shifts in Earth’s tilt, changes in Earth’s atmosphere or surface over time, and variations in the sun’s energy. These are all-natural phenomenon that caused the global temperature of Earth to warm up or cool down. These changes occurred over thousands of years; in fact, evidence suggests that as Earth moved out of ice ages, the global temperature rose 4 to 7 ˚C over 5 000 years. Climate change has always been a natural but very slow process, allowing Earth’s biosphere time to adjust to the changes occurring.

  Digging Deeper

© Mauricio Antón, via Wikimedia Commons
D7.8 Ice age climate

Did you know there is a field of science called paleoclimatology? This is the study of past climates, and it is a relatively new field of science. Scientists hope by understanding past climate changes and how they occurred, we can better predict and understand the current climate changes. Go to the following link for more information on paleoclimatology. https://earthobservatory.nasa.gov/Features/Paleoclimatology/paleoclimatology_intro.php

Learn More

© NASA
D7.4 Earth’s changing tilt
Earth’s tilt wobbles between 22.1˚ and 24.5˚. At Earth’s maximum tilt, the poles receive more solar insolation, creating warmer climates across the globe. At the minimum tilt, the poles receive less insolation, so the climates are colder.

The shape of Earth’s orbit changes over the course of about 100 000 years. It changes from a perfect circle to an oval every 50 000 years. This affects the amount of sun the earth receives during different seasons.
D7.5 Earth’s changing orbit
D7.6 Continental drift
The continental drift theory suggests that the continents have moved over the last 225 million years. At one point, all the contents fit together to form one super continent called Pangea. Pangea then split apart, and the continents drifted to the locations they are currently at. The change in the location of the continents changed the flow of the ocean currents and therefore changed how thermal energy was transferred through the ocean.
D7.7 A feedback loop
Earth’s responses can increase the effects of climate change. For example, as the earth warms, more water evaporates into the atmosphere. This evaporated water results in the formation of more clouds, increasing the cloud cover. The cloud cover will block solar radiation from reaching the earth, cooling the temperature down. The cloud cover will also block thermal energy emitted from Earth from escaping to space, increasing the temperature.

Another natural phenomenon is the amount of snow cover. As the earth cools, more snow and ice are formed on its surface. This increase in snow and ice will increase the albedo, causing more solar radiation to be reflected back into space. This would cause Earth to continue to cool, creating more snow and ice.

Please note: Earthobservatory.nasa.gov was used as a reference for the information on this page.

  Try This

Analyzing Tree Rings



Dendroclimatologists have used the growth rings in trees to gather records of Earth’s past climate data from as far back as 8 000 years. They do this by measuring the width of each of the growth rings on the trees. The wider the growth ring, the wetter the year and the longer the growing season. Tree rings are also affected by a variety of other factors, such as cloud cover, nutrients, and pests. When climatologists study the growth rings, they need to take all of these factors into account.

Click the procedure tab to continue. 
  1. Study the tree rings in image D7.9. Label each of the growth rings with a number, with 1 being the centre growth ring. The oldest part of the tree will be in the centre.
  2. Measure the width of each growth ring with a ruler and record your measurements below. You can use a rule against your screen or use this image with a ruler attached.

    Ring Number
    		Ring Width (cm)
    1
    2
    3
    4
    5
    6
    7
    8
    9
    10
    11
    12
    13
    14
    15
    16
    17

  3. Click the analysis tab to complete the analysis questions
D7.9 Tree cross-section

  1. How did the size of the tree rings change as the tree got older? What does that tell you about the climate as the tree grew?

    The tree rings got smaller as the tree got older. This tells us that the climate became drier as time went on. The growing season may have also gotten shorter due to the climate cooling. Another option is that the number of pests bothering the tree increased due to warmer winters (for example, the pine beetle).
  2. If this tree was from where you live, what do you think could have caused the pattern of these growth rings?

    Your answer will vary with where you live. Most of Alberta has been seeing a reduction in precipitation in both winter and summer over the past few years. This could account for smaller growth rings, as the tree does not have enough water to grow normally. An increase in pests could also account for smaller growth rings in heavily forested areas due to warmer winters. These warmer winters do not kill off the pests as the colder winters would have in the past. As trees get bigger, they require more nutrients to grow, so they generally do not grow as much as they get older. This is especially true of trees in areas where there are lots of other plants, such as other trees or crops.

  Take Notes

Make sure you take notes on your readings to study from later. You should focus on the factors that affected climate change in the past and how scientists study past climates. Remember, if you have any questions or you do not understand something, ask your teacher!

  Practice Questions

Complete the following practice questions to check your understanding of the concept you just learned. Make sure you write complete answers to the practice questions in your notes. After you have checked your answers, make corrections to your responses (where necessary) to study from.

  1. What period of climate does Earth currently have? How long have we been in this stage for?

    Earth currently has an interglacial climate. We have been in this interglacial climate for approximately 11 500 years.
  2. Why does natural climate change occur?

    Climate change occurs naturally through small changes in Earth’s orbit, tilt, surface, and atmosphere. It also changes as a response to previous climate changes, such as the buildup of snow and ice increasing the albedo and causing the formation of more snow and ice.