Is global warming manmade?

Global warming is caused by man

• Average global temperature has increased since the industrial revolution (with the highest average temperatures on record being the past few decades). In the past century, the temperature has increased 0.6 +/- 0.2C. This has happened in both northern and southern hemispheres.

• Greenhouse gasses have risen substantially since the industrial revolution. Carbon Dioxide (CO2) is now at its highest level in the past 800,000 years. This rise has not been a gradual one, but rises sharply after the industrial revolution (see for example data from the CSIRO). If man didn't cause this increase in CO2 then what did?

• CO2 is now around 380ppm which is around 1/3 higher than the normal maximum of 280ppm for the last half a million years. Although it does oscillate naturally (typically changing over a period of around 100,000 years) the recent changes of a similar size have happened over only a few hundred years.

• We know what the major forcings are, and how they have changed relative to 1750. There are many factors affecting the climate, but without including the affect of greenhouse gasses it is not possible to account for the increases in temperate we have seen.

• The Medieval Warm period did increase temperatures in Europe and North America. It was most probably caused by increase solar activity, and a change in "thermal-haline circulation" - ie. the gulf stream. However, in other parts of the world (eg. Antartica) temperatures decreased.

• 50 million years ago, yes, the world did have a higher CO2 concentration and what happened then should serve a warning to us today. This period is known as Paleocene-Eocene Thermal Maximum. During that time the temperature increased - the temperature of the sea rose some 5-8°C. In fact, during this time the Artic may have been ice-free. Increased CO2 in the atmosphere (from volcanoes, not man who would not evolve for tens of millions of years), and the melting of methane on the sea floor led to high levels of greenhouse gasses. The corresponding temperature increase killed off much of the existing sea life, and large numbers of our ancestors, the mammals.

• When taking a number of independant readings, the the standard error in the readings goes down. So although an individual reading may not be accurate to more than a degree, taking the average of thousands of readings gives an much smaller standard error. Therefore, it is statistically significant to talk of an error of +/- 0.2°C.

• The hockey stick graph is valid.

Global warming is not caused by man

• The average global temperature has been rising since the "Little Ice Age" that occured around the 1400s. Disregarding that dip, the average temperature has been rising for nearly 6,000 years. Medieval Warm Period

• The global warming trend graph shows that there is a change of about one degree Fahrenheit over the last 100 years. We know thermometers were not accurate to less than a degree at the beginning of the last century. The US, which generally had the best thermometers, shows less warming than the average worldwide temperature change. [1]
  
  

• If carbon dioxide is the cause for global warming, what is the cause for Mars warming?

• It has been shown that CO2 levels in the past (70 million years ago) have been as high as ten times the current amount. Also, the coldest time period in the Earth's history coincided with the highest concentration of carbon dioxide in our atmosphere ever.
  
  

• Only 3.4% of CO2 introduced every year to atmosphere is produced by man [2].
  

• In the 70s scientists panicked over a temperature shift that would cause "drastic climate change" and "destroy life as we know it." The problem was global cooling.

• Arctic ice may be receding in certain locations, but antarctic ice is increasing. The southern hemisphere is much colder. Which is consisent with the effects that would be expected to be caused by fluctuations in solar activity - more intense sunlight, as well as warming the Earth, blocks out cosmic rays. Cosmic rays have the effect of increasing cloud, so blocking them reduces cloud cover and exacerbates the warming effect, except in Antarctica where the ice is whiter, and a better reflector, than the clouds would be.
  

• The only piece of data that correlates a global rise in temperature with carbon dioxide is the "hockey stick" graph, which has been proven to be invalid. No computer model has ever been accurate for a time period as short as 4 years (El nino) even on a macroscopic scale.
  

• Over the past several million years, for as long as there has been a large land mass (Antarctica) over one polar region, the climate has followed a cycle of 100 thousand year ice ages, interspersed with 15-20 thousand year warm periods. Cycles within this cycle caused the "little ice age" amongst other effects. "Global Warming" has been ongoing since the end of the last ice age, 18 thousand years ago and current temperatures are approximately the same as those reached at the peak of the previous warm period - shortly before it returned to a state of ice age for 100 thousand years.

• Satellite-based temperature readings are more accurate than ground-based readings as they are not affected by local weather or the heatsink created by urban sprawl. These readings have shown a slight warming, then cooling, then warming again in America in recent times with no discernible, overall trend.

• Water vapour, often omitted from charts intended to show the evil of man's CO2 production, is a far greater contributor to the greenhouse effect than any other gas in the atmosphere

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