The South Cascade Glacier in Washington State, from the same point of view, from left to right in 1928, 1979 and 2003.
The year 2005 was Earth's hottest year on record, another piece of evidence that adds to the mountain of evidence tending to show that humans are causing global warming.
The Dever Post's conservtive political cartoon, Mallard Fillmore, has been humorously making the case that global warming must be natural because Mars experienced natural global warming this week.
The thing that is annoying about this is that it is pushing very hard on a straw man talking point that is obviously wrong from a scientific perspective. No one doubts that there has been climate change on Earth, Venus and Mars in history. Ice ages and the periods in between are well known in the record of ancient history. But, anyone who looks at the data knows that this doesn't explain what we are seeing now. Why?
Because the pattern of global warming we are seeing now is happening exceedingly rapidly and is closely corrolated with increasing air pollution from human activity. The graph below shows what I mean:
The top graph shows the trend of direct temperature measurements since 1860, the bottom one adds indirect temperature measurements (e.g. tree wrong and ice core based measurements) going back a thousand years. The graph below shows the very close connection between this peak in temperature and carbon dioxide levels which have changed due to human activity.
The National Academy of Science has more here.
As the most comprehensive scientific review of the evidence to date made in 2001 states:
There is new and stronger evidence that most of the Earth's warming observed in the last 50 years is attributable to human activities.
No political argument can be made with footnotes and references to scientific journals. But, making a false assumption, like the idea that global warming supporters haven't considered the possibility that natural climate changes are behind global warming (they have and have found it manifestly implausible), is little more than a lie that leads to bad policy and undermines credibility. Liberals trust solid scientific evidence. Unfortunately, conservative commentators seem to have decided that the truth doesn't matter if they can get people to believe them, and as a result, they have won many political battles. This is one case where I am not willing to copy their tactics to win. The truth is too important. Our commitment to the truth is part of what defines liberals politically.