Portland, Maine

Chart Interaction

To learn how to interact with our charts, expand the selections below.

Upper Chart

Move your cursor over the chart to reveal individual data values. To hide or show a data trace, click a term in the legend. For further instructions, mouse over the chart, then mouse over the icons that appear in the upper right-hand corner. Double click the chart to restore defaults.

Visit the Plotly© website for additional instructions on how to interact with the upper chart.

Lower Charts

Move your cursor over the chart to reveal individual data values. To move between the two charts, click an index tab.

Chart Terms & Abbreviations

To learn more about the terms and abbreviations in the charts, expand the selections below.

MMSL

Represented in light blue, the Monthly Mean Sea Level (MMSL) shows the height of the water at this tidal gauge averaged over a month of measurements. The sharp ups and downs reflect changes in water level due to storms, tidal variations, and changes in ocean and estuarine circulation. Height is measured relative to a standard elevation defined by the National Oceanic and Atmospheric Administration. See detailed discussion.

Quadratic Trend

The quadratic trend, shown in darker orange, indicates that sea level is not only rising at this tidal station, but that the rate of sea-level rise is accelerating with time. In other words, the rate of sea-level rise is best represented by a quadratic curve rather than a straight line. Comparing the quadratic and linear projections shows an exponential rise in sea level will result in a significantly higher sea level in future years. See detailed discussion.

QHi95 and QLo95

Shown in lighter orange, these confidence intervals encompass 95% of the sea-level observations recorded during each month at this tidal station, whether above (QHi95) or below (QLo95) the mean. Extending these intervals forward implies that sea level could be as much as 0.18 meters (7 inches) higher or lower than the best (quadratic) estimate of sea level during any future month out to 2050. See detailed discussion.

Linear Trend

The linear trend, shown in green, indicates how quickly sea level would rise at this tidal station with no acceleration in the rise rate (our analysis suggests this is not the case). We display the linear trend to help clarify that linear projections result in a significantly lower sea level in future years than we expect given recent observations of an accelerating rate of sea-level rise at this station. See detailed discussion.

Decadal Signal

The decadal signal, shown in dark blue, portrays ups and downs in sea level due to relatively short-term interactions between the oceans and the atmosphere, with El Niño as an example. Projections to 2050 made during an upturn in the decadal signal will be higher than they would be if the decadal signal was nearing or at a low. See detailed discussion.

Annual Linear Rate

Each year when we release our Sea-Level Report Cards, the linear rate of sea-level rise or fall will very likely change due to variations in the decadal signal and the sea-level heights observed during the intervening 12 months. The values in this plot record the linear-rate values at this station for each past year since 2004, with the time-series analysis beginning in 1969 (for a minimum series length of 36 years: 1969-2004). The linear rate is in millimeters per year (mm/yr). See detailed discussion.

Annual Acceleration Rate

Each year when we release our Sea-Level Report Cards, the rate of acceleration or deceleration will very likely change due to variations in the decadal signal and the sea-level heights observed during the intervening 12 months. The values in this plot record the non-linear rate of sea-level change at this station for each year since 2004, with the time-series analysis beginning in 1969 (for a minimum series length of 36 years: 1969-2004). The rate of acceleration or deceleration is in millimeters per year per year (mm/yr2). See detailed discussion.

Station Facts