The Polar Explorer: Sea Level app uses sets of questions to put together groups of interactive maps on similar topics. There are seven main areas, each is described here. Within each main area there are sub-areas. Each main area will have its own 'Overview of the topics' to look through. The small word description that shows when a new map is selected and the one minute audio will help the user interact with the map. The information page adds supporting information.

What is sea level?

This seemingly simple question can be answered in many ways. Here we look at three different considerations used in defining sea level. Shorelines are a marker for locating local sea level on the waterfront throughout the day. 'Elevation beneath the sea' is a measure of ocean depth telling us of both past sea level through the continental shelf, and the depth of the ocean basin. Finally the variation in height of the surface of the sea around the world, referred to as the geoid, lets us look at gravitational pull.

Why does sea level change?

Sea level is affected by many parts of the climate system. The warming of the oceans has a direct effect through 'thermal expansion' or the expansion of water as it warms causing it to take up more space. Our warming atmosphere is warming the ocean as well as melting more snow and ice in the higher elevations which we can measure in the contributions of melting ice towards sea level rise. Finally we look at the role of post-glacial or 'isostatic rebound' defined as sections of land once buried under large amounts of ice slowly rise back up as the weight of the ice is removed.

Where is sea level changing now?

First we start with a map showing tide gages that have been installed around the world to measure local sea level. Then we show a regional map with data recorded from satellites for the period 1993-2008. Our third map focuses on the U.S. coastal regions that are vulnerable to future coastal flooding.

What about the polar regions?

Users might question why an entire section of this app is devoted to the remote polar regions. The answer lies in the sea level rise potential that is tied up in the ice sheets of Greenland and Antarctica, and the neighboring high latitude glaciers. In this section you will see a range of measurements collected by different methods, many from different satellites that show the amount of ice and how it is changing. Each of these independent measures points to warming and melting of ice in the polar regions. In prior warm periods in Earth's history, ice melt from the polar regions has contributed many meters of sea level rise. The record left on the Earth suggests that the melting of ice causing sea level to rise is a much more rapid process than the creation of ice during a cold period. Studying the polar regions can help us understand the timing and extent of this process.

What about climate in the past?

Earth's history has been made up or cycles of warm and cold periods. Over the last 450,000 years cold periods have dominated with four warm periods prior to the present warm period. In this section we look at three past warm periods, about 1000 years ago, 5000 years ago, and 125,000 years ago. For past cold periods we look at the Eurasian (or Fenno-Scandia) ice sheet, the together with the Laurentide ice sheet covered much of the northern latitudes until 20,000 years ago at the end of the most recent past cold periods. The final map moves the user through deglaciation of the northern hemisphere over the last 20,000 years.

What are future predictions along the US coast?

Predictions are not guesses, they are based on a series of measurements that are combined with models to help us plan for the future. Here we look at areas that are vulnerable to a rise of up to 2m (6 ft.) of sea level.

Who is vulnerable

In this section on vulnerability we examine regions around the globe that are the most at risk from the impacts of sea level rise, bringing together science with social science indicators to evaluate human impacts; impacts both from the environment to humans and from humans to the environment. These at risk areas include low lying regions, densely populated sections of the coast, areas geographically located in the pathway of storms, floods and surges.