What is the scientific basis for AGW (anthropogenic global warming)?

The main scientific basis for anthropogenic global warming is the strong correlation between greenhouse gas emissions and global temperature increase.  In the scientific community, there is an overwhelming agreement that the increase in global surface temperatures are mainly caused by emissions of greenhouse gases.  In fact, there are no major scientific organizations that oppose the theory that global warming is caused by humans, however, a small percentage do hold noncommittal opinions.

Figure 1. Global Climate Change Attribution

Figure 1 breaks up the various factors that have an effect on global temperature change since 1900 and then pairs it with a five year average of global temperature readings.  The five factors looked at include greenhouse gases, man-made sulfate emissions, solar variability, ozone changes, and volcanic emissions (including natural sulfates).

Figure 2. Global Temperature Departure Over 1000 Years

Figure 2 shows the departure from the average temperature from the 1961-1990 average over the last 1000 years.  The blue data lines come from tree ring samples, coral samples, ice core samples, and various historical records.  The red data lines come from recent thermometer readings, and the gray shaded area represents two standard error limits.  The general shape this graph makes is nicknamed the “hockey stick”.