The earth periodically cools and warms on a large time scale. What causes this fluctuation?
The Earth's climate is quite the chaotic system, there are an infinitude of factors in the equation. Solar insolation is a big part though.
Sun The 11-year solar cycle has a great influence on space weather, and seems correlates strongly with the Earth's climate. Solar minima tend to be correlated with colder temperatures, and longer than average solar cycles tend to be correlated with hotter temperatures. In the 1600s, the solar cycle appears to have stopped entirely for several decades, with very few sunspots being seen at all, a period known as the Maunder minimum; during this time Europe experienced very cold temperatures in the Little Ice Age. Earlier extended minima have been discovered through analysis of tree rings and also appear to coincide with lower than average global temperatures.
Graph here: http://www2.sunysuffolk.edu/mandias/lia/8.jpg
This paper, "Do Models Underestimate Solar Contribution to the Recent Climate Change" by Stott et al.: http://climate.envsci.rutgers.edu/pdf/StottEtAl.pdf
In the IPCC Third Assessment Report (TAR), it was reported that volcanic and solar forcings might account for half of the temperature variations prior to 1950, but that the net effect of such natural forcings was roughly neutral since then. The change in climate forcing from greenhouse gases since 1750 was estimated to be 8 times larger than the change in forcing due to increasing solar activity over the same period.
We have a recent thread on the sun's affect on climate change: https://www.physicsforums.com/showthread.php?t=95931
Methane Clathrate Another thing that comes to mind is our friend, and local climate expert Andre's theory on the Storegga landslide.
The clathrate he refers to is methane clathrate, a form of water ice that contains a large amount of methane within its crystal structure (a clathrate hydrate).
The inlay shows methane clathrate's chemical structure. It looks sort of like a cage surrounding some methane in the middle.
Forcing Also, forcing... *eyes droop* (I'm tired)! Look at these two pictures:
Finished another paper on the clathrate today:
Dramatic climate changes occurred in the Northern hemisphere at the end of the Pleistocene. Geologic proxies as well as Greenland ice cores suggest that a more relevant change appears to be a widespread increase in precipitation that turned the cold steppe--the Mammoth megafauna habitat--into swamps and marshes in many places, especially Eurasia. Considering the rapid and radical nature of these climate changes, it cannot be attributed entirely to the warming associated with the variation in insolation that is held responsible for stadials and interglacials.
We propose that these events were caused by a massive oceanic clathrate (methane hydrate) destabilization event associated with oceanic continental slope failures of the Amazon Fan causing the excursions of many proxies during the Bolling Allerod interstadial. The destabilization in the Ormen Lange gas field area, preceding the Storegga slide, appears to have caused the excursions in the proxies that are associated with the onset of the Preboreal.
Although the amount of released methane may be limited, if not negligible, as Sowers proposes ( Science Vol 311, 10 Feb 2006 ), the physical effects of gas bubble streams are less clear. Although the released methane may dissolve and oxidize during ascent in the ocean, it may have caused turbulent water flows, disturbing the normal oceanic flow patterns. These effects have not yet been investigated and modeled. We suggest effects such as surface water with unusual temperatures flowing to abnormal areas, causing an increase of effective water surface for evaporation. These changes could have led to abnormal weather patterns generally with an increased moisture content in the atmosphere and ultimately to a substantial increase of precipitation which contributed significantly to the demise of the mammoth megafauna.
We demonstrate that the spikes of many geologic proxies, including oceanic events, appear to support this hypothesis
Not that I know much about Milankovich cycles, but I thought that had too many problems or something.
And not only the Milankovitch cycles. There are problems as well with the ice core isotope being paleo thermometers:
In a nutshell: measurements reveal that when it snows in Antartica the temperatures are above average. Which means that the ice cores, that "measure" the temperature of the snowfall intrinsically "measure" too high. But when it's warmer and it's not snowing the paleo thermometer doesn't work. And then we see an awfull tight correlation between snowfall and isotopes here.
Volcanic Activity or Magmaticity -
Arctic Mid-Ocean Ridge Expedition (AMORE) - Gakkel Ridge
Scientists underestimated the volcanic activity in this region. There is apparently a fair amount of geothermal/hydrothermal activity associated with magma in this region. Could this be partly responsible for melting of the Arctic Ocean?
What is the width of the Bering Strait? What is the depth of the Bering Strait? What is the direction of water movement in the Bering Strait? What is the temperature of the water in the Bering Strait relative to that of the Arctic Ocean? What has been the change in annual water volume through the Bering Strait over the past century?
All good questions, but from I have seen there is some speculation that the Atlantic conveyor would have a stronger influence, but the questions are then, is it stronger than normal? Is the temperature increase of the Atlantic conveyor system sufficient to cause melting of Arctic Ice? And is the increase in the temperature of the Atlantic conveyor natural or an influence of man's contribution of energy from power plants and fossil fuels/greenhouse gases?
Which of the two circulations (conveyor, Bering Strait) is more constricted? Which is more sensitive to sea level?
It would appear that the currents through the Bering Strait is more constricted (depth about 50 m), whereas the conveyor is open ocean (depth 100's-1000's m).
Here is what I found so far on currents in the Northern Pacific and Bering Sea.
North Pacific Metadatabase page
Northern Pacific Ocean Currents
Bering Sea Ocean Currents
Studying the currents of the Bering Sea using the variational data-assimilation technique: possibilities for forecasts and hindcasts of local circulation
Flow is complex and may be seasonally directional.
I am still looking for historic temperature trends.
correlation between volcanic activity and methane emissions
I was wondering if you could tell me how long the volcanos on the Gikkel ridge have been active and if there were other periods of activity in the past. I ask because I wanted to know if there is any correlation between Gikkel activity and methane clathrate emissions. Could they have a cause and effect relation which results in a runaway greenhouse effect?
Globally, volcanic activity can be measured in tenths of km3 to km3 of extruded or ejected material per year; crustal heat flows are measured in mWm-2. Doesn't melt a whole lot of ice. If you happen to be downstream from a melting icefield in Iceland, it's impressive, but not significant globally.
Heaviest snowfalls tend to occur at higher temperatures, so long as air temperature remains below freezing, because the amount of moisture the air can hold increases with air temperature. Having nearby open water, temperature even slightly above freezing, contributes to greater showfall as residents of Buffalo are painfully aware.
Geothermal activity normally doesn't play a role in temperature, but heating under ice or under water in ice covered regions can cause melting the same way putting ice over a source of heat does. An under water volcano has been discovered in the vicinity of the Larson B ice shelf in Antarctica which collapsed recently.
I wish I had found so many information about climate change before my public speaking for school!! Very informative, cool.
Thanks, on behalf of the community. If you think its cool, poke around a bit, we have a lot of really awesome stuff around here, and not just in the "Earth" section.
Methane bubbling to the surface of the water from below would also increase evaporation. Water normally needs to absorb 540 calories per gram of heat energy to evaporate at its boiling point. At normal air temperatures water may need to absorb 580 calories per gram in order to break through the surface tension of the water. If methane were disrupting that surface tension water evaporation would increase.
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