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

This animation shows the Arctic sea ice September (minimum) extents from 1979-2016. Accessible from http://nsidc.org/cryosphere/sotc/sea_ice.html

This short video clip summarizes NOAA's annual State of the Climate Report for 2009. It presents a comprehensive summary of Earth's climate in 2009 and establishes the last decade as the warmest on record. Reduced extent of Arctic sea ice, glacier volume, and snow cover reflect the effects of rising global temperature.

This is a classroom activity about the forcing mechanisms for the most recent cold period: the Little Ice Age (1350-1850). Students receive data about tree ring records, solar activity, and volcanic eruptions during this time period. By comparing and contrasting time intervals when tree growth was at a minimum, solar activity was low, and major volcanic eruptions occurred, they draw conclusions about possible natural causes of climate change and identify factors that may indicate climate change.

This video is part of the Climate Science in a Nutshell series. This short, animated video looks at evidence of a rapidly warming planet. It discusses how air bubbles in ice cores can be used to estimate Earth's average air temperature for thousands of years and how direct measurements document air temperatures from 1880.

This is an interactive graph that involves records of ice cover in two Wisconsin lakes - Lake Mendota and Lake Monona - from 1855-2010.

In this TED talk, Wall Street Journal science columnist Lee Hotz describes the research of the Western Antarctic Ice Sheet Divide project, in which scientists examine ice core records of climate change in the past to help us understand climate change in the future.

This video, from ClimateCentral, features a team of scientists from the Northern Greenland Eemian Ice Drilling Project who study atmospheric air bubbles trapped in an ice core. This work highlights a period in Greenland's ice sheet which began about 130,000 years ago and lasted about 10,000 years; a period known as the Eemian. The air bubbles from the ancient atmosphere reveal what happened with climate change over that period of time.

This video is part two of a seven-part National Academies series, Climate Change: Lines of Evidence. The video outlines, with the use of recent research and historical data, how we know that the Earth is warming.

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