Sea-level rise continues to accelerate as global ice sheets melt

Last year will likely end up as the second-warmest year on record in the Arctic. The Arctic has also been warming at twice the rate of the rest of the world. This warming, along with other factors, is contributing to the loss of land-based ice such as glaciers and ice sheets (Greenland). All of this melt water, including that from the Antarctic Ice Sheet is adding to the rise of global sea level.

Global sea level has risen an average of 21-24 centimeters (8-9 inches) since 1880. A third of that total has occurred over the last 25 years. Global sea level in 2019 was 88 mm (3.4 inches) above the 1993 average.

Global sea level rise has more than doubled from 1.4 mm/year in the 20th century to 3.6 mm/year from 2006-2015, according to NASA.

High-tide flooding in the United States is anywhere from 300 to 900 percent more frequent than it was 50 years ago.

If all of the world's glaciers and ice sheets completely melted out, they would contribute a total of 60 meters (195 feet) to the global sea level.

However, not all of the sea-level rise is due to the melting of land-based ice. Thermal expansion and land water storage are also significant contributors.

As the world's oceans continue to slowly warm due to the increase in greenhouse gases, the water becomes less dense and expands, which adds to the rise in sea level.

Groundwater from non-recharging aquifers that is consumed by humans eventually ends up in the oceans, which also contributes to the rise, but much less so.

From the 1970s to the 1990s, the melting of land-based ice and thermal expansion were almost equal contributors to global sea-level rise. However, from 2005 to 2013, the contribution from the melting of ice was nearly twice as that from thermal expansion.

Looking ahead, global sea level is expected to rise by at least 30 cm (12 inches) by the end of this century, regardless of any reductions in greenhouse gas emissions. That number could be much higher if no actions to reduce global emissions are taken.

Images courtesy NASA and NOAA.