**5. Discussion and conclusions**

There are marked differences in the thermal properties of water and air. Water has a very high heat capacity (4.187 mJ/m3 K) so that it can store or transport large quantities of heat in a given volume and it absorbs over five times as much solar energy as soil or rock since it is translucent. Currents, convection, and wave action mix the water, whereas transmission of heat energy into a rock or sediments is primarily by conduction. Water also occupies about 70% of the surface of the Earth. Air has a relatively low heat capacity although this depends on the content of water vapor which can vary from under 1% over deserts to over 4% in monsoons and tropical cyclones. Soil and rock absorb only one-fifth of the solar energy absorbed by water, and they also do not reflect back into space nearly as much solar energy as snow. Thus, the distributions of these materials at the surface of the Earth determine what energy flows are needed to produce the thermal equilibrium between the equatorial regions that receive intense solar radiation and the polar regions that receive far less direct solar energy.

The pattern of temperature change in **Figure 1** is not that of global warming. Instead, it suggests that the Northern Hemisphere is receiving more heat than the Southern Hemisphere and this sets up a system of deep saline warm (c. 22°C) water flows to the Antarctic Ocean (THC's). These are replaced by a similar flow of cold (c. 2°C) Antarctic water with more normal salinity that then accumulates in the North Atlantic where it warms up. This is believed to produce a very rapid cooling of Greenland accompanied by the growth of the glaciers there. There would also be rapid cooling of the land to the east of the North Atlantic as occurred during the Younger Dryas event (>18°C cooling, according to Isarin [92]) whereas there would be only slow warming occurring on the Antarctic ice cap. This cold air flowing eastwards would result in greater winter cooling in Siberia, thus resulting in colder air moving into North America from the cold Siberian high-pressure center in winter.

The cause of this situation is the unequal heating of the land and sea coupled with the circular outline of the Antarctic shores compared with the north-south orientated oceans connecting through gateways into the Arctic Ocean. Warm ocean currents (Gulf Stream and the Kuroshio Current) carry large quantities of warm water northwards along the east coasts of continents in the Northern Hemisphere, aided periodically by deluges of warm water from Hurricanes and Typhoons. The North Atlantic stores a great amount of heat in its surface layers, but evaporation of water into the passing westerly winds increases their salinity. This causes the warm water to sink and accumulate in the deeper water channels.

There is evidence that there is a continual loss of THC water along the deep flow route south and a counter flow back to the North Atlantic. These have decreased in volume by 15% over the last 50 years, suggesting that the THC is weakest during the warmer interglacial times. The frequent rather random changes in water temperature indicated by the δ 18O data from marine cores indicate that periodically, abrupt outbursts of THC water occur relatively frequently but do not always indicate the developments of a cold event involving major glacial advances. However, they could well be involved in causing some or all of the relatively minor cold events whose origin is discussed by Warner *et al.* [93]. Deciding whether this is their origin or

whether they are the result of Holocene outbursts of glacial meltwater into the northern oceans may be a problem.

These changes in ocean temperatures are aided by the warm Gulf Stream and Kuroshio currents that flow north along the east coasts of North America and East Asia. The shallow seas in the Bering Strait result in closing off the north Pacific Ocean from the Arctic Ocean when the sea level drops more than 50 m due to sequestering of water on land in the form of glaciers. The North Atlantic remained open to the Arctic Ocean during the last five glacial events, and the latter lost part or all of its ice cover. Cold, dry air flowing across open water picks up large amounts of moisture and heat, thus increasing the salinity and density of the sea surface. This denser water then sinks and becomes the water taking part in the THC.

The eccentricity of the Earth's orbit appears to be involved in causing the major cold events during the last 750 ka B.P., whereas obliquity caused a spacing of 41 ka between 750 ka B.P. and about 2 Ma B.P. There are numerous other cycles and one-time events that influence the day-to-day, week to week and other fluctuations in weather and climate that mask the underlying controls and movement of the plates making up the surface of the Earth slowly changed the overall pattern in terms of geological time.

There is still a lot to be found out about the thermohaline circulation in relation to climate change since the changes in sea temperature after at least 20 ka B.P. is the same for both the northern seas and the Antarctic ones [16]. It does, however, provide a viable mechanism for moving heat back from the Northern Hemisphere to the Southern Hemisphere when the difference in heat energy between the two hemispheres becomes too great.

These processes primarily affect the areas north of the Mediterranean Sea in Europe, the North Atlantic Basin, and Siberia [94]. They do not seem to affect the deserts nor the Sahel on the southern main landmasses [95, 96], while the climatic changes in Monsoon areas depend more on the climate over the source oceans.

There is no evidence to indicate that carbon dioxide is of any special importance in the processes so that the measures taken by governments to alleviate it as a problem are not needed. Society should not need to take special steps that damage or limit the economic health of economies unless it wishes to hurt itself. Data from the measuring devices in the arrays in the oceans and observations from the weather stations involved should make weather forecasting easier in the future.
