oceanic heat storage and exchange

insolation-at-65-north

Figure 2:  June Mid-Month Insolation at 65° North – click for larger image

This figure is derived from M.F.Loutre and A.Berger, 2000, Future Climate Changes: Are we entering an exceptionally long interglacial?, Climatic Change 46, 61-90

Figure 2 shows how that translates to insolation (sunshine) at 65° North.  The recent peak in insolation was 11,000 years ago at the end of the last glacial period.  It has since declined by about 10% to 476 watts per square metre. Insolation will rise from here for the next 30,000 years, but it will still be low enough for the next glaciation to form.  This is shown by Figure 3 of Northern Hemisphere ice volume for the last 200,000 years and a projection for the next 130,000 years.  According to these calculations, the Earth is at the beginning of a 20,000 year plunge into the next ice age.

The reason why the Earth doesn’t respond more rapidly to changes in insolation is due to the retained heat in the oceans, which smoothes the whole process over thousands of years.  Over the short term, the oceans are very responsive to changes in solar activity.  Figure 5 shows the very strong correlation between the annual rate of sea level rise and solar cycles over the 20th century.  The sea level rise of the 20th century can largely be attributed to a more active Sun relative to the 19th century.  About 70% of the sea level rise of the 20th century was due to thermal expansion of the oceans, with the rest due to melting glaciers….

sea-level-rise-and-solar-cycles-of-the-20th-century

Figure 4:  The Correlation between Sea Level Rise and Solar Cycles over the 20th Century. – click for larger image

The sea level data is derived from S.Holgate, Decadal rates of sea level change during the twentieth century, Proudman Oceanic Laboratory, Liverpool, UK….

Heading into a glaciation period?  Berger idea developed from:  A.L.Berger, 1978, Long Term Variations of Daily Insolation and Quaternary Climatic Changes, Journal of the Atmospheric Sciences, volume 35 (12), 2362-2367.

Eccentricity is caused by changes in the shape of the Earth’s orbit due to the gravitational attraction of other planets.  Precession is the change of direction of rotation.  Obliquity is the tilt of the axis.  When these effects aligned, their effect is reinforced….

Guest post by Dr. David Archibald

The Earth is currently in an interglacial period of an ice age that started about two and a half million years ago.  The Earth’s current ice age is primarily caused by Antarctica drifting over the South Pole 30 million years ago.  This meant that a large area of the Earth’s surface changed from being very low-albedo ocean to highly reflective ice and snow.  The first small glaciers were formed in Antarctica perhaps as long ago as 40 million years.  They expanded gradually until, about 20 million years ago, a permanent ice sheet covered the whole Antarctic continent.  About 10 million years later, glaciers appeared on the high mountains of Alaska, and about 3 million years ago, ice sheets developed on lower ground in high northerly latitudes.

Pacific Ocean bottom water temperatures started declining 40 million years ago, falling 10° C to the current 3° C. 

http://wattsupwiththat.com/2009/02/23/ice-ages-and-sea-level/

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oceanic heat storage and exchange

About half the solar energy reaching Earth is absorbed by the ocean and land, where it is temporarily stored near the surface. Only about a fifth of the available solar energy is directly absorbed by the atmosphere. Of the energy absorbed by the ocean, most is released locally to the atmosphere, mostly by evaporation and infrared radiation. The remainder is transported by currents to other areas especially mid latitudes.   -D. Stewart, Texas A & M Oceanography Dept.  http://oceanworld.tamu.edu/resources/ocng_textbook/chapter05/chapter05_01.htm

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From about 7,000 years ago until the start of the Medieval Warm Period in northern Europe, at about 1100, the water cooled gradually, by almost 1 degree C, or almost 2 degrees F. The rate of cooling then picked up during the so-called Little Ice Age that followed, dropping another 1 degree C, or 2 degrees F, until about 1600. The authors attribute the cooling from 7,000 years ago until the Medieval Warm Period to changes in Earth’s orientation toward the sun, which affected how much sunlight fell on both poles. In 1600 or so, temperatures started gradually going back up. Then, over the last 60 years, water column temperatures, averaged from the surface to 2,200 feet, increased 0.18 degrees C, or .32 degrees F. That might seem small in the scheme of things, but it’s a rate of warming 15 times faster than at any period in the last 10,000 years, said Linsley (of Columbia U., 2013).
http://phys.org/news/2013-10-pacific-ocean-absorbing-faster-years.html#jCp

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Oceans not only absorb lots of energy from the sun–they can also store lots of solar energy in the form of heat. AND they can do this with very little change in temperature. Scientists believe the way the oceans store and transport heat is related to climate.  http://oceanworld.tamu.edu/students/weather/weather1.htm

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Earth’s oceans are far more important than the land as a source of the heat energy which drives the weather. Not only do the oceans cover more than 2/3 of the Earth’s surface, they also absorb more sunlight and store more heat. Additionally the oceans retain heat longer. The Sun’s rays also penetrate the oceans to a depth of many meters, but only heat up the top layer of the sand or soil. Water has to lose more energy than the sand (dry land) in order for the temperature to decrease.  http://www.ucmp.berkeley.edu/education/dynamic/session4/sess4_act3.htm

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