The causes of global warming and climate change!

There are two competing theories for the recent global warming trend.

	The first is based on a theory which followed the warming trend that occurred between 1975 and 1998.
	The second theory is based on highly correlated data going back thousands of years.

Most agree that the temperature has increased about 0.6 - 0.7 Centigrade over the last century and that the level of CO2 or Carbon Dioxide a greenhouse gas has been increased in the atmosphere by 25-30% from pre industrial values.

	The first theory, which is the generally accepted one, is that the release of greenhouse gases from the burning of fossil fuel and from land use are responsible for the resent temperature increase.
	The second theory is that the sun's magnetic field and the solar wind modulates the amount of high energy cosmic radiation that the earth receives. This in turn affects low altitude cloud cover and how much water vapor there is in the atmosphere and thus regulates the climate.

Lets look at some data!

Fig 1. Changes in C14 concentration during the last 1000 years.

Fig 1 is from "Cosmic Rays and Earth's Climate" by Henrik Svensmark

C14 or Carbon 14 which is created from cosmic radiation is the isotope which is best known as the isotope that archeologists use for dating biological archeological artifacts. The change in the C14 concentration in the atmosphere is dominated by variations in solar activity. When the solar activity is high the production of C14 is low, this is due to the shielding effect of the solar wind against cosmic rays.

Note here that the axis for the C14 concentration has been reversed. What we then can see is that the curve closely correlates to what is historical known about the major climate events from the last 1000 years.

The Maunder minimum refers to the period 1645-1715 when very few sunspots were observed on the sun. In this period the concentration of C14 was higher in agreement with a low solar activity.

The sharp drop for C14 during the 20th century is caused by the Suess effect. This effect is due from the burning of fossil fuels which lack C14. Complicating the picture, Carbon14 was also produced by nuclear bomb tests during the cold war.

Fig 2.Solar proxies Beryllium-10 and Sunspot numbers

Solar proxies credit Global Warming Art

Because of the Suess effect, the ratio of Carbon-14 in relation to other Carbon isotopes becomes contaminated with the Carbon released from burning of fossil fuels after 1900. The C14 variation in the atmosphere as an correct indicator of cosmic radiation is less reliable after the start of industrialization.

However Beryllium-10, another isotope doesn't suffer from this effect and is therefore a better indicator of the variation of cosmic radiation for the 20th century. Here again the graph is reversed and you can also see its correlation to the sunspot numbers. From the graph it becomes clear that the amount of Be-10 have been steadily decreasing during the last hundred years indicating a decrease of the cosmic radiation and a more active Sun. The Berrylium-10 is easily dissolved in water and this record is from Greenland ice cores. The half life time of Be10 is about 1.5 million years.

Fig 3. Climate history according to IPCC 1995

From these graphs it becomes obvious that variations in the Suns solar wind and magnetic activity is a major contributor to variations in the Earth's climate.

Although we have recordings of the variations in the climate from both historical as well as from geological records we don't have an exact measurements of the average temperature with any precision. What we have are rough estimates.

This was the reason that a team led by geophysicist Michael Mann made attempts to recreate a more accurate temperature recording of the earth's climate.

Fig 4. Mann's graph is an estimate from the latest 1000 years temperature variations. Adopted by IPCC 2001

Fig 4. This graph is taken from the UNEP/GRID-Arendal site

This graph is the so called Hockey Stick graph that Michael Mann et.al. created. This graph implies that the temperature variations were relative stable during the period between year 1000 and year 1900. After that time it has increased considerably.

This graph was attacked by global warming skeptics who questioned why they could not find the Medieval Warm period and the Little Ice Age. The reason is that the graph is flawed. The graph corresponds much better to the variation of CO2 than to temperature changes. Learn more on the hockey stick anomalies HERE

Fig 5. Graph which shows the relationship between solar cycle length and the temperature.

Fig 5 The graph is taken From beam Measurement of a CLOUD, Jasper Kirkby, Cern

A stark correlation for the period 1861-1989 between the sunspot cycle length and the temperature anomaly of the Northern Hemisphere was presented by Friis-Christensen and Lassen in 1991. The temperature data comes from 1995 IPCC.

Fig 6. Shows the flux of high energy cosmic rays reaching Earth. Red line - annual averages. The blue line is an 11 yr average

Fig 6. Taken from "Carbon Dioxide or Solar Forcing?", www.sciencebits.com, Nir Shaviv

The cosmic ray flux measured by ion chambers.

The ion chambers at ground level are sensitive to high energy particles. These particles are from cosmic radiation and originate from supernova explosions with several 10's of GeV. These are the particles responsible for the formation of low altitude cover of clouds. The ionization of the upper atmosphere are mainly made from lower energy particles originating from the Sun. Plot redrawn using data from Ahluwalia (1997).

Also, the decrease in high energy cosmic rays since the 1970's are less pronounced from low energy solar activity, which means that changes in Be10 or direct solar activity are less accurate in quantifying the solar -> cosmic ray -> climate link and its contribution to 20th century global warming. This lack of clear correlation from the solar wind and low energy cosmic radiation during the last decades have been used by some climatologists to try debunk the solar climate connection.

Fig 7. Correlation between high energy cosmic radiation and low cloud cover.

Fig 7. Taken from "Cosmic Rays and Climate", www.sciencebits.com, Nir Shaviv

The cosmic ray flux as measured by Neutron count monitors at low magnetic latitudes. The low altitude cloud cover is taken from ISCCP satellite data sets, by Marsh & Svensmark, 2003.