e. Based on evidence from tree rings, other natural records, and scientific observations made around the world, Earth's average temperature is now warmer than it has been for at least the past 1,300 years. Average temperatures have increased markedly in the past 50 years, especially in the North Polar Region.

This peer-reviewed educational video explains human-caused climate change including the greenhouse effect. The role that greenhouse gases play in absorbing and re-emitting longwave radiation is illustrated. Information on how scientists know that the observed global warming is a result of human activities that burn fossil fuels is concisely explained.

This unit allows students to investigate past changes in Earth's climate. Students first explore relationships in climate data such as temperature, solar radiation, carbon dioxide, and biodiversity. They then investigate solar radiation in more depth to learn about changes over time such as seasonal shifts. Students then learn about mechanisms for exploring past changes in Earth's climate such as ice cores, tree rings, fossil records, etc.

This visualization shows static and animated images of changes in Arctic sea ice 1984-2016.

This video and accompanying article describe the work of 2 scientists on Greenland's Petermann Glacier, who are attempting to collect data from beneath the glacier to determine if the temperature of the ocean water under the glacier is playing a role in the glacier's rapid retreat.

This video is narrated by climate scientist Richard Alley. It examines studies US Air Force conducted over 50 years ago on the warming effects of CO2 in the atmosphere and how that could impact missile warfare. The video then focuses on the Franz Josef glacier in New Zealand; the glacier is used to demonstrate a glacier's formation, depth of snow fall in the past, and understand atmospheric gases and composition during the last Ice Age. Supplemental resources are available through the website.

An applet about the Milankovitch cycle that relates temperature over the last 400,000 years to changes in the eccentricity, precession, and orbital tilt of Earth's orbit.

This color-coded map displays a progression of changing five-year average global surface temperatures anomalies from 1880 through 2010. The final frame represents global temperature anomalies averaged from 2006 to 2010. The temperature anomalies are computed relative to the base period 1951-1980.

This video features scientists in New Zealand's Southern Alps, examining samples from the rocky landscape once dominated by glaciers. Their research, combined with other climate records, has revealed a link between glacial retreat and rising levels of carbon dioxide in the air.

In this activity, students are guided through graphs of surface air temperature anomaly data and Vostok ice core data to illustrate how scientists use these data to develop the basis for modeling how climate is likely to change in the future.

This activity is a research project in which students explore and synthesize key paleoceanographic evidence for the Paleocene-Eocene Thermal Maximum (PETM) as found in marine sediment cores collected and analyzed during Ocean Drilling Program Leg 208 (Walvis Ridge).