to leave room for the folks who think it is magnetic poles, or sun spots, or whatever to put their causes out there on an equal footing with greenhouse gases.  I have my opinion, that greenhouse gas buildup is the primary cause of global warming.  I note form the NOAA website: 

solar irradiance is estimated at ~0.09 W/m² compared to 0.4 W/m² from well-mixed greenhouse gases.

That suggests maybe 80% greenhouse gases and maybe 20% solar irradiance, but NOAA notes that solar irradiance does not have significant number of datapoints, we may know a lot more about solar irradiance in a couple hundred years.

As to the long list, if you want to list the items you think are causing global warming and link to science that shows some correlation, go ahead.

Finally, as you have posted, the graph showing the ppm of carbon dioxide in the atmosphere and the historical weather record shows a remarkable correlation between buildup of greenhouse gas and environmental warming.  I think the high level of correlation actually shows cause and effect, not just correlation.  I think if you pump greenhouse gases into the environment, the temperature rises.  

Is it gloom and doom to look at measurable changes in our climate that the climate scientists (not Al Gore) say are critical and engage in public discussion regarding public policy with regard to global warming?  

I don't think so. It's called science, it's called planning. 

Is it gloom and doom for the right wing folks to be concerned about terrorists and engage in public planning?  No, I may not agree with the assumptions and the plan, but it is not gloom and doom, it's planning. 

The question here is what do you think is causing global warming and why?  Are you going with the solar variability issue based on the ice caps melting on Mars?  It's a story that has some logical framework and I appreciate that part of the Mars story.

Can the observed changes be explained by natural variability, including changes in solar output?

Since our entire climate system is fundamentally driven by energy from the sun, it stands to reason that if the sun's energy output were to change, then so would the climate. Since the advent of space-borne measurements in the late 1970s, solar output has indeed been shown to vary. There appears to be confirmation of earlier suggestions of an 11 (and 22) year cycle of irradiance. With only 20 years of reliable measurements however, it is difficult to deduce a trend. But, from the short record we have so far, the trend in solar irradiance is estimated at ~0.09 W/m² compared to 0.4 W/m² from well-mixed greenhouse gases. There are many indications that the sun also has a longer-term variation which has potentially contributed to the century-scale forcing to a greater degree. There is though, a great deal of uncertainty in estimates of solar irradiance beyond what can be measured by satellites, and still the contribution of direct solar irradiance forcing is small compared to the greenhouse gas component. However, our understanding of the indirect effects of changes in solar output and feedbacks in the climate system is minimal. There is much need to refine our understanding of key natural forcing mechanisms of the climate, including solar irradiance changes, in order to reduce uncertainty in our projections of future climate change.

In addition to changes in energy from the sun itself, the Earth's position and orientation relative to the sun (our orbit) also varies slightly, thereby bringing us closer and further away from the sun in predictable cycles (called Milankovitch cycles). Variations in these cycles are believed to be the cause of Earth's ice-ages (glacials). Particularly important for the development of glacials is the radiation receipt at high northern latitudes. Diminishing radiation at these latitudes during the summer months would have enabled winter snow and ice cover to persist throughout the year, eventually leading to a permanent snow- or icepack. While Milankovitch cycles have tremendous value as a theory to explain ice-ages and long-term changes in the climate, they are unlikely to have very much impact on the decade-century timescale. Over several centuries, it may be possible to observe the effect of these orbital parameters, however for the prediction of climate change in the 21st century, these changes will be far less important than radiative forcing from greenhouse gases.