Earth's Orbit and Climate Change
Scientists have identified quasi-periodic cycles of change in the amount and distribution of solar energy reaching Earth over geologic time scales, that is, over periods of tens to hundreds of thousands of years. These cyclic changes are responsible for the waxing and waning of the Ice Ages during the last three million years. Can these cyclic changes also be responsible for contemporary patterns of climate change?
Orbital Forcing and Climate Cycles
Global climate change is one of the most profound environmental challenges facing humanity today. We have unequivocal evidence that carbon dioxide (CO2) emissions are contributing to a warming climate, but we also know that climate has changed significantly in the past, long before people were pumping CO2 into the atmosphere. What is the relative contribution of what we call "natural climate cycles" and human-caused greenhouse gases to the trajectories of change we see in contemporary climate records?
This module is aligned to the following national learning and curriculum standards:
- Climate Literacy: The Essential Principles of Climate Science
- A Framework for K-12 Science Education
- Common Core State Standards for Mathematical Practices
In this module, you will:
- Analyze the astronomical/orbital forces on the Earth's climate operating on geological timescales.
- Examine data to evaluate the possible influence of natural climate cycles on the trajectory of warming temperatures we are experiencing today in Earth's climate.
The Earth is about 4.6 billion years old, but we have instrumental measurements of temperature extending back less than 300 years. However, through ingenious detective work, scientists have been able to ascertain the history of the Earth's climate back hundreds of thousands of years using indirect means. Taken together, the isotopic composition of ice, microorganisms, and sediment, as well as our understanding of the ecological tolerances of organisms, together provide a rich and varied series of data sets that can tell us much about the climate of the past. Because these data sources do not provide a direct, instrumental record of environmental conditions, as a thermometer does, we call these sources proxy data, or "stand-in" or "surrogate" data sets.
As an analogy, what would you do if you wanted to determine if a child had a fever, and you did not have a thermometer? You would check for what you know to be biological responses to a high temperature—flushed skin, sweating, chills, a warm back or forehead, or listless behavior. If you identify one or more of these symptoms, you would likely ascertain the student had a fever. Similarly, scientists can check for the presence or absence of biological organisms, or look for gases and chemicals from which they can determine past temperatures by applying physical and chemical science principles.
Like forensic scientists in a good TV crime drama, paleoclimatologists have developed a suite of techniques and proxy data sources that allow them to reconstruct past climate with high accuracy. Just as a doctor would do a variety of tests and checks to diagnose a feverish child, scientists never rely on a single data set when piecing together the past climate. Instead, they look at many different lines of evidence, and different kinds of climate proxy sources. They test to see if others can confirm the conclusions from one proxy data source.
Set up a journal to take notes as you participate in this module. Your journal can be an online tool or offline notebook – whichever works for you and your learning style.
NASA and PBS
This professional development experience was funded by NASA's Global Climate Change Education Initiative. This initiative is designed to improve the quality of the nation's STEM (Science, Technology, Engineering, and Mathematics) education and enhance students' and teachers' literacy about global climate and Earth system change from elementary grades to lifelong learners.
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Global Climate Change Modules
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