Chapter 5. What is the reality of sea level rise?

HNRS330Hengchun Ye

Hurricane Ike’s damage to Bolivar Peninsula, Texas

Global mean sea-level 1992-2011 measured by satellite detection of the ocean surface

Sea level rise at an average of 3.18mm/yrCauses:Glacier melting, thermal expansion of sea water due to higher temperature

Damages:•Coastal erosion•Marine inundation from storms and tsunamis•raise the groundwater table and causedrainage problems•Salt water intrusion

Altimeter Studies:Using the time it takes for radar to

travel to earth’s surface and back, radar altimeter on satellites can measure the sea surface from space to better than 5cm (2 inch).

Satellites: TOPEX/Poseidon mission (1992), Jason-1 (2001), Jase-2 (2008) have mapped sea surface every 10 days for 2 decades.

Rise is not uniform around the world: fast region at western tropical Pacific; slower region at U.S. coastline; fall sea level found at west coast of U.S.

Map of sea level change 1992-2011.

Pacific Decadal Oscillation (PDO): opposite temperature variation pattern between the western pacific north of 20N and the central and eastern tropical Pacific. Each phase last 20-30 years. Positive phase (warm): western north pacific has cool water and central and eastern tropical has warm water.

Rapid sea-level rise in the western Pacific matches with negative phase of PDO. PDO has been recognized as a major factor controlling sea-level changes in the world’s largest ocean, the pacific.

PDO is thought to have switched to a negative (cool) phase in 2008. Cool phase tend to enhance La Nina conditions and suppress El Nino-like conditions. Higher water in the western tropical Pacific could continue to persists owing to strengthened trade winds.

Tide gauge studiesA water-surface-measurement devices mounted on piers, seawalls, and other coastal infrastructure to monitor the rise and fall of the tides and other changes in the ocean surface.

Water rise at 1.56mm/yr (0.06 inch) during 1962-1990; compared to 3.2mm/yr (0.13inch) between 1990-2000. Acceleration in the rise.

Coastal sediment studiesUses shoreline sediment to reconstruct the past history of sea level. Including beach sands, shallow-water corals, mud deposited on tidal flats, mangrove roots, and other.Plankton called foraminifera that collects on salt marshes that are only flooded by the highest tides. Different species of foraminifera live at different levels of the tide, a survey of the types of remains buried in marsh mud tell research where the level of the tide was in that particular spot at the time sediment layer was laid down.Radiocarbon dating: a method that permits age-dating of organic samples up to an age of about 50,000 years old.

Today’s rate of sea level rise is the most rapid of the past 2000 years. The rise has accelerated over the 20th and 21st centuries and reached more than 3mm/yr (0.13in/yr).

Sea level components1. Ocean warmingOcean stores more than 90% of the heat in Earth’s

climate system (the upper 2.5m of ocean water stores as much heat as entire atmosphere). If the energy released all at once, the atmosphere T would increases by 10C.

a. Over period 1955-2010, the heat content of the world ocean from 0-2000m depth increased by 0.09C; and from 1-700m depth it increased by 0.18C.

b. The ocean-warming component of the sea-level trend is 0.54mm/yr for depths 0-2000m and 0.41mm/yr for depth 0-700m. Deep ocean warming might have contributed 1.1mm/yr to global mean sea-level rise or 1.3 of the altimeter-observed rate of 3.11 +/-0.6mm/yr over 1993-2008.

Sea-surface temperature map from MODIS (moderate resolution imaging spectroradiometer).

2. Melting ice (accelerated melting in glaciers)Combined ice loss from Greenland and Antarctic continue

to mid-century would raises global mean se level by 15cm (5.9in).

Ice shelves: glaciers flowing into the sea can form thick floating platforms of ice

Red and pink is on GRACE satellite gravity measurement of total ice mass

Melting of ice shelves. Red is thicker ice, blue is thinner ice; melting Antarctic ice shelf is dominated by warm ocean currents sweeping along their undersides.

Antarctic has warmed at about 0.12C per decade since 1957, for a total average T rise of 0.5C. (Satellite and weather station combined)

Greenland surface melt in 2011: more-orange or fewer-blue days than the 1979-2010 average. 2011 was either the third most extensive or the sixth more extensive melting year since satellite records began in 1979. The melt season lasted up to 30 days longer than average and it affected 31% of the ice sheet surface.

A model simulation of Greenland ice in a warmer world reveals that the T threshold for melting the ice sheet completely is in the range of 0.8C to 0.32C of global warming. Warming already reached the minimum of this range (0.8C).Melting the total ice on Greenland would result in a sea-level rise of about 6.5m and affect many of the world’s major cities, which are located on coastlines because of historical ties to shippingIce losses quickened in 2006-08 to the equivalent of 0.75mm/yr of sea-level rise.

Other components of sear-level rise:Retreating mountain glaciersEarth’s glaciers and ice caps outside of the regions of Greenland and Antarctica are shedding roughly 150 billion tons of ice annual and sufficient to raise global mean sea level approximately 0.4mm/yr.

The GRACE mission consists of two satellites (launched in 2002) that orbit earth together 16 times a day at an altitude of about 482 km. Traveling together, the two satellites sense subtle variations in Earth’s mass and gravitational pull caused by regional changes in the planet’s mass, including ice sheets, oceans, and water stored in the soil and in underground aquifers.

Total sea-level rise from all land-based ice on Earth including Greenland and Antarctica was roughly 1.5mm/yr annually from 2003-2010

Changes in ice thickness (cm/yr) during 2003-2010 as measured by NASA’s Gravity Recovery and Climate Experiment (GRACE) satellites. Blue: ice mass los; red: ice mass gain

Vulnerability of the Honolulu region from sea-level rise of 0.9m. Blue indicates sea level 0.9m above present high tide; red indicates groundwater inundation when se level is 0.9m above present high tide

Sea-level rise will likely cause increased coastal erosion, saltwater intrusion, drainage problems, marine inundation, and flooding when it rains

U.S. approximately 32,000KM2 of land lies within one vertical meter of the high tide line, encompassing 2.1 million housing units where 3.7 million people live.Rise in sea-level will cause coastal water table rise, possibly to the point of breaking through the ground surface and creating new wetlands.

Under 1.2m of sea-level rise, the tourist mecca of Waikiki, Hawaii, would be severely affected by seawater inundation at high tide, and the negative impacts of this would ripple throughout the tourism-based economy of the entire state of Hawaii. Red indicates buildings located at modern high tide. Orange indicates buildings vulnerable to 1ft (0.3m) of sea level rise. Yellow indicates buildings vulnerable to 2ft sea-level rise. Green indicates buildings vulnerable to 3ft sea-level rise. Purple indicates buildings vulnerable to 4ft sea-level rise.

Challenges:Adopting to the unavoidable consequences of present warming and mitigating the worse of future warmingAdopting to sea-level rise is a process unending series of expenses, decisions, and construction projects lasting through this century and into the next.GIS: geographical information system. Is used in develp map layers depicting community assets, including vulnerable ecosystems, social phenomena, transportation assets and other key features of the coastal zone.

Sea-level rise from 1990 to 2011 based on IPCC AR4 temperature projections for three different emission scenarios. Red: observation-based annual global sea-level data

CGCMs mean sea-level anomaly (m) with regard to global mean sea-level change (1.02m) for scenario A1B between 1980-1999 and 2090-2099, for a scenario with adapted ice sheet contributions of 0.22m for the Greenland ice sheet and 0,41 m for the Antarctic ice sheet.There are significant regional differences in sea level rise: North Atlantic, Southern Ocean experiences negative sea level rise; Pacific and Indian oceans positive sea-level rise.

Sea-level Change during 1970-2010. Yellow: tide-gauge data; red: satellite data; blue: high and low projections of the IPCC.The scientific community is converging on a consensus that it is a appropriate to plan for a 1 m rise in mean sea level by the end of the century.