12.17: Global Warming

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How can things change so quickly?

Glaciers and ice sheets are melting. This can be seen clearly in photographs. The glaciers advanced during the Pleistocene ice age. They have been melting back since then, except for during the Little Ice Age. However, the rate of melting has increased tremendously in recent decades.

Temperature Variations

Since the end of the Pleistocene, Earth’s temperature has risen. The image below shows how it changed over just the last 1500 years (Figure below). The Medieval Warm Period was a time of somewhat higher average temperatures. The Little Ice Age was a time of somewhat lower average temperatures. But for each time, the anomaly (the difference from average temperature) was less than 1° C (1.8° F). Still, the overall trend is slightly upward.

Earth's temperature over time has increased

Earth’s temperature. Different sets of data all show an increase in temperature since about 1880 (the Industrial Revolution).

Recent Temperature Trends

Since the mid 1800s, Earth has warmed up quickly (Figure below). By end the of 2017, 17 of the 18 hottest years on record have all occurred since 1998! This temperature rise is what is usually meant by global warming.

Graph showing the increase in Earth's temperature over the last 150 years

Earth’s temperature (1850–2007). Earth has really heated up over the last 150 years. Do you know why?

Summary

Average global temperature has been rising since the end of the ice ages.
The largest temperature rise has been in the past two decades.
The rise in Earth's temperature since the late 19th century is referred to as global warming.

Review

What have been the temperature trends in the past 1500 years?
How is the rise in temperatures in the past two decades different from the rise since of the past 1500 years?
What is global warming?

Explore More

Use the resource below to answer the questions that follow.

How much has the global temperature risen in the last century?
What is the major human activity that contributes to global warming and why?
What is the greenhouse effect?
Is average global temperature rising? What is your evidence?
Which greenhouse gases are at their highest levels in history? When was the last time they were as high?
What do researchers predict will happen?
What can we do now to slow the rise in temperatures?