How has the temperature changed in the last 140 years?

How has the temperature changed in the last 140 years?

Difficulty Rating: Medium . Academic Discipline: Earth Science . Keywords: Public lecture, carbon, Keeling Curve, climate change, CO2

Standards: Scale, weather and climate, Constancy and Change

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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 the 2006 public lecture "Will the Living Climate Save Us From Climate Change?", Peter Cox explains how basic measurements of the Earth's average climate show a warming trend over the last 140 years. Dr. Cox points out the cooling during the 1940's through the 1960's and a resumption of warming from the mid 1970's until the present. He attributes the cooling period to the effect of aerosols, such as sulfate aerosols, temporarily countering the warming effect of carbon dioxide. The overall trend, however, reveals a warming of the global average atmosphere, warming that is occurring at an unprecedented rate.

To veiw the complete video of the lecture, click here.

HOW do we know?

As evidence that the Earth is warming, Dr. Cox shows the global temperature record from thermometers at weather stations and ships from all over the world dating back into the mid-19th century. The red bars are individual years. The black lines that look a bit like whiskers in each bar represent the uncertainty in the measurements for each year. The heavy blue line is a running average which shows the general trend of the data. The change in temperature is about 0.7 deg C and is shown as a departure, or anomaly, from the 1961-1990 average. The associated image shows a more recent version of the same graph that Dr. Cox shows from the Met Office Hadley Centre.


WHY can this be trusted?

The graph displayed by Dr. Cox is iconic and has been supported since its creation by additional data and research. It represents temperature records gathered from teams of scientists in different countries, pooling together data to create a world-view of changing temperature, and it provides an example of climate change detection. Its upward trend depicts recent warming of the past several decades that do not follow the natural variability in the Earth's temperature, either in magnitude of the change in temperature or the rate at which it is occurring. See the attached graph from NASA for a recent example of a similar diagram.


The research of Dr. Cox and his colleagues offers a clear, evidenced-based representation of how the planet is changing. An increase in the average global temperature could lead to drastic changes in local climates, shifts in weather patterns, or even changes in biodiversity. Research on how temperatures have changed over the last few centuries help scientists to infer potential human impacts and project how global temperatures might shift in the future, allowing for an opportunity to plan and prepare for potential changes.

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Further Reading
Further Reading: 

To watch the complete public lecture from Peter Cox, visit the AGCI website.

To learn more about temperatures graphs and their construction, visit NASA's webpage