The system is broken
There are a number of things we "know" as a society today. Individual opinions and disagreements exist, but society as a whole "knows" a number of things to be true. Many of our actions (and indeed personal opinions) are decided by using these truths as a basis. We act as though these truths cannot be proven false--they're truths, right
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For example, it is a fact that warmer air is capable of holding more water vapor. It is theorized that a warmer atmosphere would be capable of producing more clouds. The clouds would reflect a larger percentage of solar radiation than clear air, which would decrease the amount reaching the surface. There would be an increase in infrared radiation re-radiated from the clouds back to the surface, but the net effect would likely be cooling.
To say global warming is not a lie does not mean it's completely caused by humans. We only have around 100 years of good observational data plus thousands of years of proxy data through ice cores (there are other proxy sources as well). There's a possibility that we've downplayed the role of natural effects. That was the point that Petr Chylek (who happens to be my advisor at Los Alamos National Lab) and his collaborators made in his 2004 paper in Climate Change in which he shows that the cooling trend in Greenland seems to be correlated to the North Atlantic Oscillation (NAO). The NAO is a large-scale effect in the strength of the subtropical high (in the Atlantic) and the Icelandic low, which affect weather patterns and ultimately the temperature in the northern Atlantic region.
As for the publication by Doran and his collaborators, they do show that there is a cooling trend in Antarctica, but they are focusing more on the ecosystem response and they do not talk about the ice sheet response directly. By the way, it is no secret that the Antarctic ice sheets are thickening, especially in the inland areas. It is so cold there that it would take significant warming for those ice sheets to stop growing and begin to melt. The coastal ice sheets may be a different story, but I don't know much about that. It is the depletion of alpine glaciers, small ice sheets in the mountain ranges in the low to middle latitudes that are a particular cause of concern, as these areas would be more sensitive to temperature rises above freezing and significant depletion has already been observed.
The CO2 levels in the atmosphere tell a compelling story. They start to rise after the industrial revolution and nonlinearly increase within the 20th century. It shows strong evidence that humans have affected the global climate. It is also known that an increase in atmospheric CO2 will absorb more infrared radiation from the surface and re-radiate it back to the surface, meaning less infrared radiation will escape the atmosphere, causing a net temperature increase. This is traceable through other atmospheric constituents as well.
There are many publications that try to predict the magnitude of warming in the future and those are viewed with a great deal of skepticism. Much like weather forecasting models, climate models can be wrong and have a greater chance of being wrong as they step forward in time. However, by using many model runs with differing parameters, general conclusions can be made about the average effect observed by the models.
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