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 video describes the role that dendrochronology plays in understanding climate change, especially changes to high elevation environments at an upper tree line. Dendrochronologists from the Big Sky Institute sample living and dead trees, describe how correlations between trees are made, and explain how tree cores record climate changes.

This web-based activity tackles the broad reasons for undertaking ocean exploration - studying the interconnected issues of climate change, ocean health, energy and human health. Students examine the types of technology ocean scientists use to collect important data.

This video is the second of three short videos showcasing the dramatic changes in Alaska's marine ecosystems. The video highlights the marine mammals and birds and how they depend on Arctic sea ice, as well as questions about how these animals will cope in the face of climate change.

This is a figure from the 2007 IPCC Assessment Report 4 on atmospheric concentrations of carbon dioxide, methane and nitrous oxide over the last 10,000 years (large panels) and since 1750 (inset panels).

These graphs show carbon dioxide measurements at the Mauna Loa Observatory, Hawaii. The graphs display recent measurements as well as historical long term measurements. The related website summarizes in graphs the recent monthly CO2, the full CO2 Record, the annual Mean CO2 Growth Rate, and gives links to detailed CO2 data for this location, which is one of the most important CO2 tracking sites in the world.

This video features changes in the land, sea, and animals that are being observed by the residents of Sachs Harbour, Northwest Territories, Canada â many of whom hunt, trap, and fishâbecause of their long-standing and intimate connection with their ecosystem. Scientists interview the residents and record their observations in order to deepen our understanding of climate change in the polar region. Background essay and discussion questions are included.

This video discusses two key signs of global change in the Southern Ocean: changes in Antarctic bottom water and ocean acidification.

In this activity, students investigate how scientists monitor changes in Earth's glaciers, ice caps, and ice sheets. The activity is linked to 2009 PBS Nova program entitled Extreme Ice.

This video follows biologist Gretchen Hofmann as she studies the effects of ocean acidification on sea urchin larvae.

This video segment, from the 'Earth: The Operators' Manual' featuring climate expert Richard Alley, shows how ice cores stored at the National Ice Core Lab provide evidence that ancient ice contains records of Earth's past climate - specifically carbon dioxide and temperature.

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