Editing IPCC:AR6/SROCC/Chapter-1 (section)

== Box 1.1 Major Components and Characteristics of the Ocean and Cryosphere ==

<div id="article-1-1why-this-special-report-block-1"></div>

'''Ocean'''

The global ocean is the interconnected body of saline water that encompasses polar to equatorial climate zones and covers 71% of the Earth surface. It includes the Arctic, Pacific, Atlantic, Indian and Southern Oceans, as well as their marginal seas. The ocean contains about 97% of the Earth’s water, supplies 99% of the Earth’s biologically habitable space, and provides roughly half of the primary production on Earth.

Coasts are where ocean and land processes interact, and includes coastal cities, deltas, estuaries, and other coastal ecosystems such as mangrove forests. Low elevation coastal zones (less than 10 m above sea level) are densely populated and particularly exposed to hazards from the ocean (Chapters 4 to 6, Cross-Chapter Box 9). Moving into the ocean, the continental shelf represents the shallow ocean areas (depth &lt;200 m) that surround continents and islands, before the seafloor descends at the continental slope into the deep ocean. The edge of the continental shelf is often used to identify the coastal ocean from the open ocean. Ocean depth and distance from the coast may influence the governance and economic access that applies to ocean areas (Cross-Chapter Box 3 in Chapter 1).

The average depth of the global ocean is about 3,700 m, with a maximum depth of more than 10,000 m. The ocean is vertically stratified with less dense water sitting above more dense layers, determined by the seawater temperature, salinity and pressure. The surface of the ocean is in direct contact with the atmosphere, except for sea ice covered regions. Sunlight penetrates the water column and supports primary production (by phytoplankton) down to 50 – 200 m depth (epipelagic zone). Atmospheric-driven mixing occurs from the sea surface and into the mesopelagic zone (200 – 1,000 m). The distinction between the upper ocean and deep ocean depends on the processes being considered.

The ocean is a fundamental climate regulator on seasonal to millennial time scales. Seawater has a heat capacity four times larger than air and holds vast quantities of dissolved carbon. Heat, water, and biogeochemically relevant gases (e.g., O 2 and CO 2 ) exchange at the air-sea interface, and ocean currents and mixing caused by winds, tides, wave dynamics, density differences and turbulence redistribute these throughout the global ocean (Box 1.1, Figure 1).

'''Cryosphere'''

The cryosphere refers to frozen components of the Earth system that are at or below the land and ocean surface. These include snow, glaciers, ice sheets, ice shelves, icebergs, sea ice, lake ice, river ice, permafrost and seasonally frozen ground. Cryosphere is widespread in polar regions (Chapter 3) and high mountains (Chapter 2), and changes in the cryosphere can have far-reaching and even global impacts (Chapters 2 to 6, Cross-Chapter Box 9).

Snow is common in polar and mountain regions. It can ultimately either melt seasonally or transform into ice layers that build glaciers and ice sheets. Snow feeds groundwater and river runoff together with glacier melt causes natural hazards (avalanches, rain-on-snow flood events) and is a critical economic resource for hydropower and tourism. Snow plays a major role in maintaining high mountain and Arctic ecosystems, affects the Earth’s energy budget by reflecting solar radiation (albedo effect), and influences the temperature of underlying permafrost.

Ice sheets and glaciers are land-based ice, built up by accumulating snowfall on their surface. Presently, around 10% of Earth’s land area is covered by glaciers or ice sheets, which in total hold about 69% of Earth’s freshwater (Gleick, 1996 <sup>[[#fn:r28|28]]</sup> ). Ice sheets and glaciers flow, and at their margins ice and/or melt water is discharged into lakes, rivers or the ocean. The largest ice bodies on Earth are the Greenland and Antarctic ice sheets. Marine-based sections of ice sheets (e.g., West Antarctic Ice Sheet) sit upon bedrock that largely lies below sea level and are in contact with ocean heat, making them vulnerable to rapid and irreversible ice loss. Ice sheets and glaciers that lose more ice than they accumulate contribute to global sea level rise.

Ice shelves are extensions of ice sheets and glaciers that float in the surrounding ocean. The transition between the grounded part of an ice sheet and a floating ice shelf is called the grounding line. Changes in ice shelf size do not directly contribute to sea level rise, but buttressing of ice shelves restrict the flow of land-based ice past the grounding line into the ocean.

Sea ice forms from freezing of seawater, and sea ice on the ocean surface is further thickened by snow accumulation. Sea ice may be discontinuous pieces moved on the ocean surface by wind and currents (pack ice), or a motionless sheet attached to the coast or to ice shelves (fast ice). Sea ice provides many critical functions: it provides essential habitat for polar species and supports the livelihoods of people in the Arctic (including Indigenous peoples); regulates climate by reflecting solar radiation; inhibits ocean-atmosphere exchange of heat, momentum and gases (including CO 2 ); supports global deep ocean circulation via dense (cold and salty) water formation; and aids or hinders transportation and travel routes in the polar regions.

Permafrost is ground (soil or rock containing ice and frozen organic material) that remains at or below 0°C for at least two consecutive years. It occurs on land in polar and high mountain areas, and also as submarine permafrost in shallow parts of the Arctic and Southern Oceans. Permafrost thickness ranges from less than 1 m to greater than 1,000 m. It usually occurs beneath an active layer, which thaws and freezes annually. Unlike glaciers and snow, the spatial distribution and temporal changes of permafrost cannot easily be observed. Permafrost thaw can cause hazards, including ground subsidence or landslides, and influence global climate through emissions of greenhouse gases from microbial breakdown of previously frozen organic carbon.

<div id="article-1-1why-this-special-report-block-2"></div>

<span id="box-1.1-figure-1"></span>
<!-- START IMG -->
<!-- IMG TITLE -->
'''Box 1.1, Figure 1'''

<span id="box-1.1-figure-1-climate-change-related-effects-in-the-ocean-include-sea-level-rise-increasing-ocean-heat-n-content-and-marine-heat-waves-ocean-deoxygenation-and-ocean-acidification-section-1.4.1.-changes-in-the-cryosphere-include-the-decline-of-arctic-sea-ice-extent-antarctic-and-greenland-ice-sheet-mass-loss-glacier-mass-loss-permafrost-thaw"></span>
<!-- IMG CAPTION -->
'''Box 1.1, Figure 1 | Climate change-related effects in the ocean include sea level rise, increasing ocean heat n content and marine heat waves, ocean deoxygenation, and ocean acidification (Section 1.4.1). Changes in the cryosphere include the decline of Arctic sea ice extent, Antarctic and Greenland ice sheet mass loss, glacier mass loss, permafrost thaw […]'''
<!-- IMG FILE -->
[[File:e1b17cf8e94756f855586a3a366d8a3b IPCC-SROCC-CB_1_1.jpg]]

Box 1.1, Figure 1 | Climate change-related effects in the ocean include sea level rise, increasing ocean heat n<br />
content and marine heat waves, ocean deoxygenation, and ocean acidification (Section 1.4.1). Changes in the cryosphere include the decline of Arctic sea ice extent, Antarctic and Greenland ice sheet mass loss, glacier mass loss, permafrost thaw and decreasing snow cover extent (Section 1.4.2). For illustration purposes, a few examples of where humans directly interact with ocean and cryosphere are shown.

<!-- END IMG -->
<span id="role-of-the-ocean-and-cryosphere-in-the-earth-system"></span>