Wow, you don't? Understanding the science behind the change is as easy as 1-2-3:
1. Climate change has happened before due to CO2, with disasterous effects on life at the time:
http://www.killerinourmidst.com/P-T%20boundary.html
"As a greenhouse gas, it warms the atmosphere, changing ecological conditions. (Deccan Traps volcanism, coming before the end of the Cretaceous, is estimated to have warmed the world by 3° to 5°C, or 5.4° to 9°F; Ravizza and Peucker-Ehrenbrink, 2003.) And because it combines chemically to form carbonic acid, it also produces mildly acidic rain. Acid rain can dissolve calcium carbonate shells, particularly those at or near the ocean surface. Additionally, acid rain leaches vital nutrients from the soil, resulting in plant stunting and death."
Climate Model Links Warmer Temperatures to Permian Extinction
http://www.physorg.com/news6003.html
"The CCSM indicated that ocean temperatures warmed significantly at higher latitudes because of rising atmospheric levels of carbon dioxide, a greenhouse gas. The warmer temperatures reached a depth of about 10,000 feet (4,000 meters), interfering with the normal circulation process in which colder surface water descends, taking oxygen and nutrients deep into the ocean.
As a result, ocean waters became stratified with little oxygen, proving deadly to marine life. Because marine organisms were no longer removing carbon dioxide from the atmosphere, that, in turn, accelerated warming temperatures.
"The implication of our study is that elevated [carbon dioxide] is sufficient to lead to inhospitable conditions for marine life and excessively high temperatures over land would contribute to the demise of terrestrial life," the authors conclude.
Climate simulation of the latest Permian: Implications for
mass extinction
http://www.cgd.ucar.edu/ccr/aboutus/staff/kiehl/Kiehl-Shields.pdf
2. The timing for current warming is unexpected, contrary to the cooling solar influence of natural Milankovich cycles:
An often-cited 1980 study by Imbrie and Imbrie determined that "Ignoring anthropogenic and other possible sources of variation acting at frequencies higher than one cycle per 19,000 years, this model predicts that the long-term cooling trend which began some 6,000 years ago will continue for the next 23,000 years."
3. We can identify the amount of CO2 that mankind has inserted into today's atmosphere from the ratios of different carbon isotopes:
http://environmentalchemistry.com/yogi/environmental/200611CO2globalwarming.html
So in summary, climate change has happened due to CO2 before and the results were devastating to life, the timing of the change is not what we'd expect from other explanations such as solar radiation cycles due to orbital changes, and we have measured mankind's increased in atmospheric CO2 levels.
In short, we're causing exactly the type of change that has been devastating to life on this planet in the past.
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We could still make the argument that "There are no absolutes in science" or ask the questions "How sure are they?" and "What about the skeptical scientists?" Here is what the balance looks like in terms of scientific evidence:
http://norvig.com/oreskes.html
The consensus was quantified in a Science study by Prof. Naomi Oreskes (Dec. 2004) in which she surveyed 928 scientific journal articles that matched the search [global climate change] at the ISI Web of Science. Of these, according to Oreskes, 75% agreed with the consensus view (either implicitly or explicitly), 25% took no stand one way or the other, and none rejected the consensus.
Counting only peer-reviewed papers published in reputable journals is important because they are cross-checked by scientist peers who are also staking their professional reputations on the validity of the paper including its evidence and its conclusions.
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For more background on the history of the science behind greenhouse gas theory, here's a good summary:
http://www.aip.org/history/climate/co2.htm
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As for convincing you however, that can't be done; you will decide for yourself what you choose to believe. You can lead a horse to water, but you can't make it drink.
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Edit -
Dan R's response contains good links that handle most of the common skeptical responses to the theory. They're not scientifically sound, but as long as you don't look into the science too deep they make great reasonable-sounding excuses for people to feel good about remaining in denial.