The Thermo-haline et al

The thermohaline circulation (Fig. 1)  is that part of the ocean circulation which is driven by density differences. Sea water density depends on temperature and salinity, hence the name thermo-haline. The salinity and temperature differences arise from heating/cooling at the sea surface and from the surface freshwater fluxes (evaporation and sea ice formation enhance salinity; precipitation, runoff and ice-melt decrease salinity)... It can be regarded as a big overturning of the world ocean, from top to bottom

But this "conveyor belt", which acts as the world's thermostat, is slowing due to global warming.

The largest source of the coldest water in the world's oceans ceased producing Antarctic Bottom Water in 1976. The surface water around Antarctica, which has be been freshening since the 1950's, formed a lid of low-density water stopping the overturning process in the Weddell sea near the coast of Antarctica. The Weddell Sea polynya, an area of open water the size of New Zealand, was the most productive source of cold Antarctic bottom water in the 1970s. Relatively warm salty water is pushed upwards by ocean currents moving over a ridge in the Weddell sea. Before 1980 this salty water reached the surface releasing large amounts of heat, then cooled and sank to the bottom of the ocean. The heat kept the huge hole in the ice pack called a polynya open, and a massive oceanic convection cell formed in the Antarctic winter. This convection cell cooled the global oceans while warming the air around Antarctica. Antarctic Bottom Water, the most voluminous water mass in the oceans, is now being replaced by warmer, less dense water masses as the deep oceans warm.

Which means...

The strengthened winds have spun up the strong current that rings Antarctica called the Antarctic Circumpolar Current. This ring of fast moving water tends to block the transport of warm subtropical water towards Antarctica. However, the geography of the northern hemisphere has the opposite effect on the poleward transport of warm subtropical water. The Atlantic ocean is aligned to funnel warm subtropical water into the Arctic ocean as the subtropical highs strengthen and the trade winds speed up. Thus, the collapse of the Weddell Sea polynya has lead to increased transport of oceanic and atmospheric heat towards the Arctic. The rapid warming of the Arctic and the extraordinarily rapid decline of Arctic sea ice, which was not predicted by climate models, is a likely consequence of the collapse of the Weddell Sea polynya, which had been the most productive source of Antarctic Bottom Water (ABW). The authors of this report don't discuss the effects of the end of Weddell Sea bottom water formation on the global ocean circulation or the Arctic (the discussion here is based on my extensive review of paleoclimatology research) but they do hint at the importance of the decline in ABW formation.

Which means... the jet stream is weakened as well because when the arctic becomes warmer, the temperature gradient from north to south lessens, thus causing the jet stream to lose strength and move south as a result, which enables such events as the Polar Vortex and intense snow storms to occur with greater frequency.

  

A study in 2001 found that stratospheric circulation can have anomalous effects on the weather regimes.[29] In the same year researchers found a statistical correlation between weak polar vortex and outbreaks of severe cold in the Northern Hemisphere.[30][31] In more recent years scientists identified interactions with Arctic sea ice decline, reduced snow cover, evapotranspiration patterns, NAO anomalies or weather anomalies which are linked to the polar vortex and jet stream configuration.[29][31][32][33][34][35][36][37] However, because the specific observations are considered short-term observations (starting c. 13 years ago) there is considerable uncertainty in the conclusions. Climatology observations require several decades to definitively distinguish natural variability from climate trends.

Summing it up, does global warming exist when taking in all these factors? Yes, particularly if there's an increase in anomalies, the precursors to phase transitions, where one state replaces another due to an environmental change such as heat, the agent that transforms water into a solid, a liquid or to a gas, depending on how hot the environment gets. 

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Earth's Northern Hemisphere over the past 30 years has seen more "hot" (orange), "very hot" (red) and "extremely hot" (brown) summers, compared to a base period defined in this study from 1951 to 1980. This visualization shows how the area experiencing "extremely hot" summers grows from nearly nonexistent during the base period to cover 12 percent of land in the Northern Hemisphere by 2011. Watch for the 2010 heat waves in the Middle East, Western Asia and Eastern Europe, and the 2011 heat waves in Texas, Oklahoma and Mexico. Credit: NASA/Goddard Space Flight Center Scientific Visualization Studio

Addendum, Click 15 Seconds, a short BRT bulb showing just how hot the world has become in the last 60 years. Something for thought if you ask me.