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Hydrosphere

Overview of Climate Change Research > Hydrosphere

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 glossary glossary terms  

Click for definitions of words used on this page:

heat capacity
coral bleaching
El Niño
La Niña
positive feedback
negative feedback


View the full, printable version of the glossary.

Overview of Climate Change Research Hydrosphere
hat We Know: Underlying Processes

The oceans play a key role in regulating the earth’s climate—and yet they remain mysterious, because so many of the basic processes underlying ocean dynamics are still poorly understood. Their fundamental role in climate is based largely on their storage and transport of heat around the globe. The oceans store vast amounts of heat, much more than the heat stored by the atmosphere,because water is 1000 times more dense and has a heatholding capacity four times that of air. Ocean currents are primary highways for the transport of heat around the globe.

The global thermohaline ocean circulation

Differences in water density drive ocean currents. The density of seawater is controlled by the water’s temperature and salinity, a combination summed up in the term thermohaline (thermo refers to temperature, haline to salinity).


The North Atlantic showing Gulf Stream

The warm ocean current known as the Gulf Stream, shown in this satellite image of sea surface temperatures, transports heat from the Gulf of Mexico to northwestern Europe. In this image, yellow indicates a temperature of 23C (73F, green is about 14C (57F), and blue is about 5C (41F).


The Gulf Stream, for example, is a wind-driven surface ocean current originating in the Gulf of Mexico and terminating in northwest Europe. When water from this warm current evaporates, it warms the air—which is why northwestern Europe enjoys a milder climate than Canada at the same latitude.

The driving force behind the Gulf Stream and other ocean currents is simple physics: In the waters west of Europe, the evaporation of water makes the sea saltier and colder, which makes the water more dense.

The denser water sinks and warmer surface water streams in to replace it, providing the current’s sustaining pull.
Since this simple physical process is based on the interaction of warmer and colder masses of water, global climate change could seriously disrupt that interaction.
Evidences and Uncertainties
Changes in water temperature could disrupt ocean currents, slowing or even shutting them down. A shutdown of the Gulf Stream would drastically change the climate of the countries ringing the North Atlantic Ocean, leading to significant cooling in these areas. Some fossil evidence suggests that past shutdowns in the Gulf Stream were associated with previous ice ages. For this reason, some researchers argue that a small increase in global temperatures could actually initiate a sudden cooling trend—a negative feedback loop in which changes in one direction spark larger shifts in the opposite direction. Another possible effect of continued warming on the oceans is a significant rise in sea levels. Some of this would result from the melting of polar ice, but the largest proportion of the increase would be caused by thermal expansion. (Water, like all things, expands as its temperature rises.)

Evidence suggests that sea levels have risen by 10 to 15 cm (about the width of your fist) over the past one hundred years. Continued rises in sea levels could have devastating effects on islands whose entire living space lies only a few meters or less above sea level. The Indian Ocean’s Maldive Islands, for example, have a mean height of 1 m above sea level; even small increases in sea levels could completely devastate tiny nations like this. But forecasting the amount of sea level rises must allow for a wide range of uncertainty: One recent estimate, drawn from a report by the Intergovernmental Panel on Climate Change (IPCC), suggests a possible range of between .09 and .88 meters of increase over the next century. (See “Average Annual Global Number of People Flooded under Three Emissions Scenarios” on this site for information on the consequences of rising sea level.)
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Global Climate Change: Research Explorer: Primer: Overview of Climate Change Research : Hydrosphere
Global Climate Change The Exploratorium
home atmosphere hydrosphere cryosphere biosphere global effects
   
Hydrosphere

Overview of Climate Change Research > Hydrosphere

Page 3 of 6

 glossary glossary terms  

Click for definitions of words used on this page:

heat capacity
coral bleaching
El Niño
La Niña
positive feedback
negative feedback


View the full, printable version of the glossary.

Overview of Climate Change Research Hydrosphere
hat We Know: Underlying Processes

The oceans play a key role in regulating the earth’s climate—and yet they remain mysterious, because so many of the basic processes underlying ocean dynamics are still poorly understood. Their fundamental role in climate is based largely on their storage and transport of heat around the globe. The oceans store vast amounts of heat, much more than the heat stored by the atmosphere,because water is 1000 times more dense and has a heatholding capacity four times that of air. Ocean currents are primary highways for the transport of heat around the globe.

The global thermohaline ocean circulation

Differences in water density drive ocean currents. The density of seawater is controlled by the water’s temperature and salinity, a combination summed up in the term thermohaline (thermo refers to temperature, haline to salinity).


The North Atlantic showing Gulf Stream

The warm ocean current known as the Gulf Stream, shown in this satellite image of sea surface temperatures, transports heat from the Gulf of Mexico to northwestern Europe. In this image, yellow indicates a temperature of 23C (73F, green is about 14C (57F), and blue is about 5C (41F).


The Gulf Stream, for example, is a wind-driven surface ocean current originating in the Gulf of Mexico and terminating in northwest Europe. When water from this warm current evaporates, it warms the air—which is why northwestern Europe enjoys a milder climate than Canada at the same latitude.

The driving force behind the Gulf Stream and other ocean currents is simple physics: In the waters west of Europe, the evaporation of water makes the sea saltier and colder, which makes the water more dense.

The denser water sinks and warmer surface water streams in to replace it, providing the current’s sustaining pull.
Since this simple physical process is based on the interaction of warmer and colder masses of water, global climate change could seriously disrupt that interaction.
Evidences and Uncertainties
Changes in water temperature could disrupt ocean currents, slowing or even shutting them down. A shutdown of the Gulf Stream would drastically change the climate of the countries ringing the North Atlantic Ocean, leading to significant cooling in these areas. Some fossil evidence suggests that past shutdowns in the Gulf Stream were associated with previous ice ages. For this reason, some researchers argue that a small increase in global temperatures could actually initiate a sudden cooling trend—a negative feedback loop in which changes in one direction spark larger shifts in the opposite direction. Another possible effect of continued warming on the oceans is a significant rise in sea levels. Some of this would result from the melting of polar ice, but the largest proportion of the increase would be caused by thermal expansion. (Water, like all things, expands as its temperature rises.)

Evidence suggests that sea levels have risen by 10 to 15 cm (about the width of your fist) over the past one hundred years. Continued rises in sea levels could have devastating effects on islands whose entire living space lies only a few meters or less above sea level. The Indian Ocean’s Maldive Islands, for example, have a mean height of 1 m above sea level; even small increases in sea levels could completely devastate tiny nations like this. But forecasting the amount of sea level rises must allow for a wide range of uncertainty: One recent estimate, drawn from a report by the Intergovernmental Panel on Climate Change (IPCC), suggests a possible range of between .09 and .88 meters of increase over the next century. (See “Average Annual Global Number of People Flooded under Three Emissions Scenarios” on this site for information on the consequences of rising sea level.)
Page 3 of 6
next


home | atmosphere | hydrosphere | cryosphere | biosphere | global effects

about this site - © 2002 The Exploratorium