b. Environmental observations are the foundation for understanding the climate system. From the bottom of the ocean to the surface of the Sun, instruments on weather stations, buoys, satellites, and other platforms collect climate data. To learn about past climates, scientists use natural records, such as tree rings, ice cores, and sedimentary layers. Historical observations, such as native knowledge and personal journals, also document past climate change.

This short video, adapted from NOVA, explains how Earth's position relative to the Sun might be responsible for the dramatic shift in the climate of what is now the Saharan nation of Djibouti.

This NBC Learn video features climate scientists doing their research on Mt. Kilimanjaro to study the climate of the past. The scientists put the recently observed changes on the glacier into perspective by comparing past climate fluctuations, stressing that the current observed rate of change is unprecedented.

This video explores the work of environmentalist John Hart, a Professor of Environmental Science at U.C. Berkley. In the Rocky Mountains of Colorado, Dr. Hart has established an experimental laboratory in which he has artificially created and maintained a 3-degree increase in surface temperature of a plot of land, and documented the impact on plant species occupying the plot.

This video, along with a background essay, focuses on impacts of climate change on the lives of Native Alaskans around Barrow, Alaska. Specific changes include the timing of the changes in the formation and breakout of sea ice and the impacts on subsistence living.

This short video from NASA discusses the role that salinity plays in Earth's climate and ocean circulation, focusing on the observations of the Aquarius satellite.

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