Global warming is caused by man. As man continues to change the composition of the atmosphere, it affects the climate. Although the temperature responds to both natural and man-made influences (known as forcings), recent warming...
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Global warming is caused by man. As man continues to change the composition of the atmosphere, it affects the climate. Although the temperature responds to both natural and man-made influences (known as forcings), recent warming cannot be explained without including the changes in composition of the atmosphere. In particular, the level of CO2 and other greenhouse gasses in the atmosphere (eg. methane) play important roles in the climate which cannot be ignored. * 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. In response to the case against global warming, we would like to point out that: * 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. In conclusion, man is causing a change in the composition of the atmosphere. The observed rise in global temperature cannot be explained without including these changes. Man is causing global warming. Edit this argument.
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