Approximately half of the carbon emitted since the Industrial Revolution persists in the atmosphere today. The balance is presumed to have made its way into the oceans or to have been incorporated into organic matter on land. Uptake of CO2 by the oceans is limited by the supply of carbonate ions, CO32- , in surface waters, so that a chemical reaction takes place whereby CO2 and CO32-, plus water, react together to give bicarbonate ions (HCO3-).

Thus carbon is absorbed into the oceans, and the seas become more acid as this happens...

Carbon dioxide is a weak acid, and inclusion of CO2 in the oceans leads to a reduction in pH, transforming carbon from CO32- to bicarbonate ions, HCO3- , and dissolved neutral carbon. There is a limit, however, to how much the sea will act as a 'sink' in this way.

Alkalinity can be altered only by the addition of salts, which are supplied, for example, by the dissolution of calcite, CaCO3 , in sediments. The CO32- content of waters at the ocean surface is small, and sustained uptake of CO2 requires that CO32- be supplied continuously to the surface. Over a 100-year period about 10 percent of the water in the oceans is exposed at the surface. If such is the case, only 30 percent of the carbon dioxide released to the atmosphere by burning fossil fuels can be incorporated into the sea.

Variations in the Earth's orbit around the Sun can cause variations in the distribution and seasonality of solar radiation, which in turn may result in climatic changes. The orbital variation effect has been identified clearly in the geologic, glaciologic, and biotic record of the past 300,000 years, but it is less successful in explaining climatic conditions dating farther back in time

The geometry of the Earth's orbit around the Sun affects how solar radiation is distributed over the surface of the planet. The latter is determined by three orbital parameters that have cyclic frequencies: (1) the eccentricity of the Earth's orbit i.e. its departure from a circular orbit), with a frequency of about 100,000 years, (2) the obliquity, or tilt, of the Earth's axis away from a vertical drawn to the plane of the planet's orbit, with a frequency of 41,000 years, and (3) the precession, or wobble, of the Earth's axis, with frequencies of 19,000 and 23,000 years. Collectively these parameters determine the amount of radiation received at any latitude during any season; radiation curves have been calculated from them for different latitudes for the past 600,000 years. These curves vary systematically from the poles to the equator, with those in the higher latitudes being dominated by the 41,000-year tilt cycle and those in lower latitudes by the 19,000- and 23,000-year precession cycles. The theory that the changes in the earth's orbit were important in 'recent' climate change places emphasis on summer insolation in the high-latitude areas of the Northern Hemisphere (about 55° N latitude). Glaciations are hypothesized to begin during times of low summer insolation when conditions should be most optimal for winter snow to last through the summer season.

Orbital variations, moreover, can only be used to explain fluctuations on the order of 1,000 years or more, because all three components—precession of the equinoxes, obliquity, and eccentricity—work on long, predictable time scales.

It is generally agreed that the waxing and waning of ice sheets and variations of sea level can be related to these parameters in the past 300,000 years, as can many aspects of Holocene variation, notably the monsoons.

The following extract has been taken from Wikipedia, and indicates that predictions can only be made on time scales of 20,000 years or more:

The seminal paper of Hays, Imbrie and Shackleton 'Variations in the earths orbit: pacemaker of the ice ages' qualified its predictions with "forecasts must be qualified in two ways. First, they apply only to the natural component of future climatic trends - and not to anthropogenic effects such as those due to the burning of fossil fuels. Second, they describe only the long-term trends, because they are linked to orbital variations with of 20,000 years and longer. Climatic oscillations at higher frequencies are not predicted... the results indicate that the long-term trend over the next 20,000 years is towards extensive Northern Hemisphere glaciation and cooler climate". http://environment-agency.resultspage.com/search?p=Q&ts=ev2&w=crc&x=15&y=14

Yes. When there are more sunspots, there is more radiation, and therefore heat, from the sun. (There have been no sunspots for some time now, and therefore the sun is radiating a little bit more than usual.) There are also natural variations in its output over time, and at the moment the average (over the past 20 years or so) is at a relatively high value. See the link to the right for more on this.

www.climate4you.com

Yes. Of course there are no exact values, but estimates can be made from such things as the thickness of rings in trees, from ice that has been laid down at the Poles, etc. The first person to do this (Michael E Mann) came up with a chart that showed slight changes up to about 100 years ago, then a very sharp increase in the last 100 years or so. This graph was termed the 'Hockey Stick' chart because of this. Other contributors have also come up with graphs that looked like this. Since there are no natural variations that could reasonably cause this, then this is very good evidence for man-made climate change causing an increase in average global temperature, in recent times.

See wikipedia's article on the 'Hockey Stick graph' ...

(from one of Iain Stuart's programmes - 'Earth: the Climate Wars' - as seen on the Eden channel, 11/3/11)