How much ice has to melt to change the conveyer belt of the atlantic that makes europe warmer than n. america?

Question

how much fresh, cold water would have to be put into the atlantic ocean via the melting of ice to cause a change to the 'conveyer belt of the atlantic' that takes warmer tropical water, brings it up next to the western coast of europe, including the UK to a point whereby the western coast of europe and the UK will experience famine as a result of colder weather?

for example, must all of the north pole melt? how much ice is on greenland that would cause this to happen? wouldn't much of greenland's melted ice just flow as water into the ground?

how many icebergs must melt?

is there change that all of the ice on antarctica would melt? how much climate change would melt all of that ice, and what would the result be down under the equator?

Answer 1

Its not really known exactly how much, so I think we should do the experiment and warm the earth until this happens.  Then we will know for sure.

Answer 2

A lot of questions, I'll see what I can do...

The Gulf Stream is a complicated one and no-one knows what effect, if any, global warming will have.  There is a theory that meltwater runoff from the Arctic and Greenland Ice Caps could interupt the Gulf Stream.  Unfortunately this isn't something that can be tested in practice so a lot of it is based on guess work.

The Gulf Stream is part of the larger Thermohaline Circulation (also called Meridional Overturning Circulation or MOC for short).  The Gulf Stream (also known as the Atlantic Conveyor), is probably the most well known of the ocean currents but there are several other.  These currents are driven by the density of the water which is affected by two things - salinity and temperature (thermo = temperature, haline = salt).  A change in either could impact on the Gulf Stream but the two are in conflict.  I'll explain...

Meltwater is cold and fresh, in comparison the oceans are warm and salty.  Cold water is more dense than warm water so the meltwater would flow UNDER the Gulf Stream but at the same time, freshwater is less dense than saltwater so would flow OVER the Gulf Stream.  What may happen is effectively a head on collision between meltwater and Gulf Stream, this could be enough to knock the Gulf Stream off course and divert it elsewhere or it could push it backwards so that, for example, the warmer waters are only carried as far as the Mid Atlantic.

If the Gulf Stream were 'switched off' or diverted then the coastal regions of northwest Europe would see a temperature drop of up to 10 degrees Celsius. Living conditions would change but there wouldn't be famine.  The countries that would be affected are well developed and have the ability to import food as needs be.  The decline in crop production could partially be offset by an increase in livestock farming.

As for how much melting would be needed - no-one knows, a substantial amount and probably considerably more than there is at present.

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Almost all of Greenland is a frozen mass, the melting that occurs is on the surface and the meltwater can't penetrate the ground because of the ice underneath, instead it forms rivers and streams that flow over the ice and through passages in the ice.  There is also melting around the edges, the meltwater here enters the ocean sraight away.

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There's no chance that all of Antarctica will melt - not for a very long time.  The Antarctic interior is bitterly cold and very substantial temperature rises would be needed to melt the ice in these regions.  Even if we did everything possible to try and melt the ice it would take thousands of years.