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Below are notes from a climate change conference on the 18th November 2006 at Sussex University.

My brief notes from the talk are meant to be read alongside the Powerpoint presentation prepared by Dr Paul Williams (Most of the slides are self-explanatory, however there are a few which need a little explanation). I have tried to note down things that were either not mentioned in the Powerpoint presentation or that Paul elaborated on in the talk.

The Gulf Stream Switch Off? - Dr Paul Williams

GLOBAL SURFACE TEMPERATURE 1861-2004

- There has been a 0.7 degree centigrade rise in temperature since 1900

NORTHERN HEMISPHERE SURFACE TEMPERATURE 1000-2000

- Temperatures started rising 50 years after the industrial revolution started because there is a time-lag of several decades between the release of carbon dioxide and the eventual temperature rise it causes. In this way, children really do suffer from their parents emissions.

ATMOSPHERIC CO2 OVER THE PAST 400,000 YEARS

- There is now evidence to show that CO2 emissions are higher now than any time over the last million years ago (not just the 400,000 years shown on the graph)

HOW HOT WILL IT GET?

- The red lines show range of potential temperature increase.
- There is a consensus that a dangerous temperature increase would be around 2 degrees Centigrade. This is the temperature at which serious climatic effects could have widespread impacts.

PROJECTED IMPACTS OF CLIMATE CHANGE

- The purpose of this talk was to look at the "risk of abrupt and major irreversible changes." In particular, the chance of the gulf stream slowing down or switching off.

THE THERMOHALINE CIRCULATION

- Due to the Thermohaline Circulation (or Gulf Stream), Europe is 10 degrees centigrade warmer than if it did not exist. This is equivalent to the heat released from one million power stations.

HOW THE GULF STREAM WORKS - A SIMPLIFIED EXPLANATION

- Water at the equator is warmed and evaporates which makes the water saltier. This warm current moves north. As the water becomes saltier (with more evaporation along the way), it becomes denser and eventually it sinks around Greenland.  
- With the ice caps melting the saltiness of the water is reduced. If the water becomes less dense, it does not sink so easily. If the polar ice cap melts more, the water could potentially not sink at Greenland but further south. The melting sea ice could dilute the saltiness of the sea and shut (or shift) down the gulf stream.
- However, if the Gulf Stream slows down, the water would have more time to evaporate and therefore becomes saltier. There are other impacts which could happen, and hence there is a variety of computer models exploring different possibilities (see below).
- Wikipedia provides a more in-depth discussion as well as links to several papers on the subject: "The evaporation of ocean water in the North Atlantic increases the salinity (relative saltiness) of the water as well as cooling it, both actions increasing the density of water at the surface. The formation of sea ice further increases the salinity. This dense water then sinks and the circulation stream continues in a southerly direction. Global warming could lead to an increase in freshwater in the northern oceans, by melting glaciers in Greenland and by increasing precipitation, especially through Siberian rivers."

IMPACTS ON TEMPERATURE

- If the gulf stream did shut down it would become 8 degrees centigrade cooler over Europe and 1 degree centigrade warmer in some parts of Africa. This 8 degree centigrade cooling over North West Europe would more than cancel out the projected 2 degree centigrade increase in temperature this century due to global warming.
- If the gulf stream did shut down it would 10 years for this cooling to take place. This would also result in the global net production of vegetation decreasing by 5%.

WHAT ARE THE CHANCES OF THE GULF STREAM SHUTTING DOWN?

There are a few ways of trying to figure this out:

1) Observations
2) Computer Models
3) Asking the experts

METHOD 2: COMPUTER MODELS

- There are a multitude of different models which all disagree on what will happen with the gulf stream.
- There is a huge uncertainty with the models BUT if you look at the average of all of the different models, it indicates that the gulf stream will shut or slow down. The models vary widely on the extent to which this will happen.

METHOD 3: ASK THE EXPERTS

- At a recent climate change conference in Swansea, everyone present was handed a questionnaire which asked two questions
- The results of the survey showed that the people who had the most expertise in climate change were the people that thought that the gulf stream shutting down was the least probable.