What do rising sea levels cause

A third, much smaller contributor to sea level rise is a decline in the amount of liquid water on land—aquifers, lakes and reservoirs, rivers, soil moisture. This shift of liquid water from land to ocean is largely due to groundwater pumping. In the early 20th century, the glacier met the water and calved icebergs into a marginal lake near the bay. By , the glacier had retreated, leaving behind sediment allowed the lake to be transformed into a small grassland.

Photos courtesy of Louis H. Pedersen and Bruce F. Large images: From the s up through the last decade or so, melting and heat expansion were contributing roughly equally to observed sea level rise.

But the melting of mountain glaciers and ice sheets has accelerated:. As a result, the amount of sea level rise due to melting with a small addition from groundwater transfer and other water storage shifts from — was nearly twice the amount of sea level rise due to thermal expansion. Melt streams on the Greenland Ice Sheet on July 19, Ice loss from the Greenland and Antarctic Ice Sheets as well as alpine glaciers has accelerated in recent decades.

Sea level is measured by two main methods: tide gauges and satellite altimeters. Tide gauge stations from around the world have measured the daily high and low tides for more than a century, using a variety of manual and automatic sensors.

Using data from scores of stations around the world, scientists can calculate a global average and adjust it for seasonal differences. Since the early s, sea level has been measured from space using radar altimeters, which determine the height of the sea surface by measuring the return speed and intensity of a radar pulse directed at the ocean.

The higher the sea level, the faster and stronger the return signal is. Observed sea level since the start of the satellite altimeter record in black line , plus independent estimates of the different contributions to sea level rise: thermal expansion red and added water, mostly due to glacier melt blue. Added together purple line , these separate estimates match the observed sea level very well. To estimate how much of the observed sea level rise is due to thermal expansion, scientists measure sea surface temperature using moored and drifting buoys , satellites, and water samples collected by ships.

Temperatures in the upper half of the ocean are measured by a global fleet of aquatic robots. Deeper temperatures are measured by instruments lowered from oceanographic research ships.

When water shifts from land to ocean, the increase in mass increases the strength of gravity over oceans by a small amount. From these gravity shifts, scientists estimate the amount of added water. As global temperatures continue to warm, sea level will continue to rise.

How much it will rise depends mostly on the rate of future carbon dioxide emissions and future global warming. How fast it will rise depends mostly on the rate of glacier and ice sheet melting. The pace of sea level rise accelerated beginning in the s, coinciding with acceleration in glacier and ice sheet melting.

In , at the request of the U. Their experts concluded that even with lowest possible greenhouse gas emission pathways, global mean sea level would rise at least 8 inches 0. With high rates of emissions, sea level rise would be much higher, but was unlikely to exceed 6. Interagency Sea Level Rise Taskforce. Based on their new scenarios, global sea level is very likely to rise at least 12 inches 0. On future pathways with the highest greenhouse gas emissions, sea level rise could be as high as 8.

Observed sea level from tide gauges dark gray and satellites light gray from , with future sea level through under six possible future scenarios colored lines. The scenarios differ based on potential future rates of greenhouse gas emissions and differences in the plausible rates of glacier and ice sheet loss. Since the report report, new research has emerged showing that some of the more extreme estimates of how quickly those ice sheets could melt were more plausible than they previously seemed.

Along almost all U. For the densely populated Atlantic seaboard north of Virginia and the western Gulf of Mexico, sea level rise will likely be higher than the global average for all pathways. On the bright side, if future energy choices keep us on one the three lowest pathways, Alaska and the Pacific Northwest are likely to experience local sea level rise that is less than the global average.

In all cases, however, rising sea levels are increasing coastal flood risk. High-tide flooding is already a serious problem in many coastal communities, and it is only expected to get much worse in the future with continued rising seas. These data are for education and communication purposes only.

They are documented in Church and White It is based on a weighted average of global tide gauge records collected by the U.

The weights for each gauge in the global mean are determined by a cluster analysis that groups gauges from locations where sea level tends to vary in the same way. This prevents over-emphasizing regions where there are many tide gauges located in close proximity.

The most recent year of data should be considered preliminary. Cassotta, S. Chapter 3: Polar regions. Roberts, V. Masson-Delmotte, P. Melting has outpaced snowfall, and the loss of ice has been greatest on mountain glaciers in the mid-latitudes and tropics and on the Greenland ice sheet. Melting ice can produce a positive feedback loop - darker areas especially oceans, but also land beneath the high-albedo snow or ice absorb more light than the bright snow or ice had done, and thus warm still further, melting more snow and ice.

This will be further discussed in the next week of the course. Melting ice can alter the salinity of seawater as freshwater is added to the ocean. Changes in salinity alter seawater density, which can change major ocean currents that transport heat through the ocean driven by the currents, stimulating more climate change. Complete melting of glaciers and ice sheets would raise sea levels worldwide almost 70 meters feet above current levels.

Melting glaciers would add another half of a meter. For some perspective on all this melting ice, consider this: sea level has risen about meters since the last glacial maximum approximately 20, years ago when ice covered large parts of the Northern Hemisphere and wooly mammoths roamed the Earth.

Misconception Alert: Not all melting ice causes sea level rise! As ice on land melts, water flows into the ocean, and sea level rises. But sea ice, the stuff that forms a frozen cap floating on top of the water, does not affect sea level. Like ice cubes in a glass of water, the sea ice does not affect the volume in the glass as it melts. Ice is less dense than liquid water; that's why ice floats.

When ice melts, it becomes denser; the same mass fits into a smaller volume. The change in volume exactly offsets the extra bit of the ice that was sticking up above the water's surface. Melting sea ice is a sign of climate change and, in fact, causes more warming through the ice-albedo feedback. Melting sea ice also changes ocean salinity the sea ice only has a little salt in it, so it essentially releases fresh water as it melts and ocean temperature.

These changes can alter ocean currents, which also affect climate. East Coast. Another analysis based on NASA and European data skewed toward the higher end of that range, predicting a rise of 26 inches 65 centimeters by the end of this century if the current trajectory continues. If all the ice that currently exists on Earth in glaciers and sheets melted it would raise sea level by feet. That could cause entire states and even some countries to disappear under the waves, from Florida to Bangladesh.

In the meantime, scientists keep refining their models of sea-level changes. They also point out that the extent to which countries work together to limit release of more greenhouse gases may have a significant impact on how quickly seas rise, and how much. All rights reserved.

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