This reply is just to bring a little science to potential causes of climate shifts.
The movie, "The Day After Tomorrow", is a super dramatization that the climate is all of a sudden going to shift, because the Thermohaline circulation in the North Atlantic Ocean all of a sudden breaks down and essentially brings a major shift to the world wide weather patterns...
That was Hollywood of course, and nothing is going to happen overnight. But, it was based on the idea that the oceans play a huge role in our weather and regional climates. Unlike the atmosphere, water stores energy for a much longer time, as we surfers can see in the fall when it takes water temps off the East Coast longer much longer to cool. And, this is the just the surface temperatures... As a whole the ocean, which makes up some 70+% of the earth's surface is a huge storage of energy.
Water temps have large impacts on the regional climate of areas (west coasts see this more easily since weather moves from west to east). Take a look at Europe - England is further north in latitude then Newfoundland, but has a much more moderate climate. This is because the warm gulf stream provides relatively warm water off the west coast of Europe.
The gulf stream is more of a surface current, but the thermohaline is driven by ocean density differences by changes in thermo-temperature and haline-salt the create a huge conveyor belt of ocean circulation from the ocean surface to the ocean floors that are interconnected throughout all of our oceans.
Changes in the thermohaline circulation in the North Atlantic has been claimed as reasons for previous past climate shifts. In the present day "climate change", in the North Atlantic we look at ice melting (less saline = less density) and water temps rising (less density), which can change the sinking motion of the all important North Atlantic Thermohaline circulation.
So, I'm not replying to anyone in particular, I just wanted to offer a science example to how and why climate shifts can occur.
I wish global warming were legit. I mean real numbers, not inaccurate readings that have only risen 1 degree in how ever many years. As a scientist in the field (not in a lecture hall), the margin of error in these temperature readings from around the globe using various instruments are astronomical. So anyway, this sucks. I'm sick of the cold. I vote for a 30 degree above avg winter!!! And a bunch of Nor'Easters.
Yesterday was fun as hell, some serious bombs coming through. The water is getting cold from climate change (summer to winter). Wish I didn't have to work right now!! I should just go occupy wall street!!!
In our lifetime, we've already seen sea level rise. It's being measured by satellite as we speak... about 2 or 3mm/year, on average. That translates into the landward migration of the shoreline over time. I've seen the effects of it myself... in Cape May County, wooded areas adjacent to salt marsh that were once high and dry are now swamps where trees are rotting and falling into the back bays. That in itself is not such a tragedy, but you can assume that this is happening in many coastal plains around the world, where salt water is intruding into fresh water wells... where habitats are changing and endangering species... where agricultural land used to raise food or feed for animals is becoming less productive... where people are being forced to move from their dwellings...
And my guess is... to bring it all back into focus... shoreline ocean currents are changing, and changing the way sand moves and how the waves break. That's not such a big stretch of logic...
Aloha everyone, 1st post.
If I may add my 2 cents to this discussion I'll just suggest this: Someone who's spent years studying for their PhD and then publishing peer-reviewed research is a bit like someone who's put in the time at a competitive break to get it dialed and earn their spot in the lineup. They're not gods, and some may be douchey, but still...
You hit the nail on the head, its all about the thermohaline circulation which at the surface is largesly a response to the overlying atmospheric circulation. However, the circulation of deeper waters is a conseqence of density variations which result from differences in temperature and salinty. In areas where surface waters become denser due to cooling/evaporation (increasing salinity) waters will sink to a level where they equilibriate with surrounding water masses. Additionally areas of sea ice formation produce brine which increase water density casuing water to sink and form dense cold water masses. These dense water masses flow away from their source areas. Much of the world's oceans are filled with Antarctic Bottom Water. In the Atlantic, the deepest waters are characterized by North Atlantic Deep Water (NADW) that form primarliy in the Norweigan and Greenland Seas.
The NADW forms north of 60N and the NADW water mass moves south at depth bringing cooler, saline water to the South Atlantic and other basins (at depth). This "loss" of cooler water in the northern lats is compensated by the poleward movement of warm saline surface waters to the North Atlantic (via Gulf Stream and/or North Atlantic Drift). These waters are responsible for the mild temperatures Western Europe experiences even in winter. The combination of NADW formation in the north and the movement of warm salty water to higher latitudes is considered a linked system, sometimes referred to as the NADW conveyor belt. Disturbances to this system can cause a change in its speed or even shut it down. In particular, the system can be quite sensitive to distrubances from freshwater inflows. Currently the North Atlantic Basin loses slightly more freshwater via evaporation than it gains frome either precipitation or river runoff. This combined with the flux of saline Gulf Stream water and strong cooling (as in winter) leads to NADW formation. However, were the freshwater flux to increase (as it has in the past when ice sheets melted), an upper, lower salinity layer would be created where this NADW formation would be altered, or shut-down. This would in a sense turn the conveyor belt "off" and a reduction in the flux of Gulf Stream water to the northern latitudes. This in turn means less heat transported to the North Atlantic and generally colder climates. Cold climates would continue until eventually salinity would gradually increase to some critical density whereby the conveyor would switch back on.
It has been postulated that this is what brought the last interglacial to a close (Cortijo et al., 1994; Shaffer and Bendstren, 1994). In addition to orbital forcing (reduction in summer insolation and and increase in winter insolation), a higher interglacial sea level would have led to an increased flux of water through the Arctic from the North Pacific bringing more low salinity water to the North Atlantic. Higher temperatures may have increased in evaporation and precipitation rates adding additional freshwater to the North Atlantic. It is thought that these factors would have been enough to lower surface water density and reduce or even eliminate deepwater production, setting the stage for renewed continental glaciation. Once temperatures fall, the evaporation rates would also have decreased allowing salinity levels to remain low. The only caveat to the above scenario is that all these factors are related in a positive feedback loop which makes distinguishing causes and effects, difficult.
So the take home reader's digest version is that the thermohaline circulation is a critical driver of climate but is also very susceptible to changes in freshwater/salinity fluxes. Were the climate to increase in temperatures to unprecedented levels, there would be an increase in freshwater influx to the system (due to higher temps). Over time were the flux of freshwater to become large enough it would trigger the slowdown or cessation of NADW production. The effects of this would reduce ocean circulation of warmer waters to higher latitudes. And turning off the conveyor belt could trigger a return to cooler climates (in the North Atlantic anyway). So in a way mother nature has a solution to changes in climate whether temperatures increase or decrease.