However, more distant climatic history proves that the Earth's climate has been changing for a long time, and will continue to change for a long time no matter what we do. Our contribution is not zero, but there is no evidence to indicate that it is dominant either.

However, the Far Left will blame President Bush for absolutely everything, including the recent tsunami, so why not global climate change? The suspect that Bush probably caused the start of the present ice age some 2 million years ago.

Read this for a brief explanation:
History of Global Warming

The last paragraph of that article is quoted here:
In the period of time that was previously mentioned (0-1850 AD) there were 5 major factors in the changing of the Earth's climate. They were: the orbit of the Earth around the sun, the variations of the sun's energy, the levels of Greenhouse Gases, sparse Volcanic eruptions, and random changes in the atmosphere and oceans.

Here is another perspective:
Global Warming: A Chilling PerspectivePutting things in perspective, geologists tell us our present warm climate is a mere blip in the history of an otherwise cold Earth. Frigid Ice Age temperatures have been the rule, not the exception, for the last couple of million years. This kind of world is not totally inhospitable, but not a very fun place to live, unless you are a polar bear.

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Except for two relatively brief interglacial episodes, one peaking about 125,000 years ago (Eemian Interglacial), and the other beginning about 18,000 years ago (Present Interglacial), the Earth has been under siege of ice for the last 160,000 years.

From which this chart is taken:

Earth's temperature over past 160,000 years.
It looks similar to the other one above, but time increases from right to left in this one.

This chart shows recent history from: http://www.physicalgeography.net/fundamentals/7x.html

Near-global annual-mean temperature change for the period 1880 to 1999

This chart shows carbon dioxide and temperature levels over the past 150,000 years.

Please note that time increases from right to left, not the other way, in this chart. Most recent data in on the left, older data on the right. (From: http://www.geocraft.com/WVFossils/global_warming.html)

Note, that temperature was increasing steeply from about 20,000 years ago until about 9,000 years ago, and has been decreasing since then. (This does not show the past century.)

In other words, the entire issue is very vague and will probably remain so.