50 million years of Earth’s temperature: Are we going back to the future? (2/2)

50 million years of Earth’s temperature: Are we going back to the future? (2/2)

Difficulty Rating: Medium . Academic Discipline: Earth Science, Geology, Social Psychology . Keywords: carbon, climate change

Standards: Science and Society, Models, Scale, Graphs, Systems and Cycles

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Clip Guide

Clip Guide

: Here you will find clear descriptions of what you just saw, how they know what they said they knew, why they know it to be trustworthy information. Finally we will ask the question, "So what!" and explore why the information is important.

WHAT do we know?

In this clip from "Nature Visible and Invisible," Dr. Kiehl describes his perception of how visible and invisible aspects of our world impact on human actions relating to climate. He then uses a graph to display the temperature record of the last 100 million years on Earth, as gathered by studying oxygen isotopes. He explains that in the past Earth was much warmer that is it today, but models suggest that fossil fuel emissions may return our climate to a previous, warmer state at a rate much more rapid than has occurred before in the known history of the planet.


HOW do we know?

Dr. Kiehl’s graph is drawn from models that use current knowledge about carbon output and rates of energy use increase. Using this information, scientists can make educated guesses about how a system, such as Earth’s climate, may behave in the future.

WHY can this be trusted?

Scientists such as Dr. Kiehl are able to use models to make reasonable predictions about the future because there are many physical relationships we understand well enough to represent quantitatively.  For example, carbon dioxide is known to be a greenhouse gas—a type of gas that traps long wave radiation in the atmosphere—and scientists understand pretty well the amount of energy that each amount of greenhouse gas is able to add to the climate system. Therefore, models are able to represent the impact of changing atmospheric concentrations of carbon dioxide on global average temperature.


In this presentation, Dr. Kiehl uses models to indicate that within just a few human generations, the Earth’s average temperature could increase by 2-5 degrees Celsius (a change that would represent a major change in the Earth’s climate). The last known time when such a shift occurred, it took 50 million years to take place. The combined effects of the new, rapid rate of change and the significant amount of change would have major impacts on life as we know it, including: sea-level rise, agricultural impacts, extinction, water availability, and large changes in land and aquatic ecosystems. Avoiding these impacts will depend upon understanding the relationship between greenhouse gas emissions and temperature rise. Graphs such as Dr. Kiehl’s help to explore this relationship.

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Further Reading
Further Reading: 

The complete PowerPoint of this presentation is available on AGCI's website.

Kiehl, J. (2011). Lessons from Earth’s Past. Science. 331: 158-159. Access to this article requires a subscription; however, there is a free summary available at in Science Daily.

M.L. Parry, O.F. Canziani, J.P. Palutikof, P.J. van der Linden and C.E. Hanson (eds). Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA. 976 pp