The BBC has compiled a list of the top ten reasons "climate skeptics" dispute the evidence that human activities such as industrial emissions of greenhouse gases and deforestation are bringing potentially dangerous climate change as claimed by the Intergovernmental Panel on Climate Change (IPPC). Counter arguments made by some of scientists who agree with the IPCC are also presented in the BBC presentation. The comparison is much too long to duplicate here, but can be found at the BBC site.
My personal view is that we are undergoing global warming at a rate that cannot be explained by historic natural cycles. There is a compelling trend, shown on the referenced graph, that the average combined global land and marine surface temperature has been rising since 1860 and that increased concentrations of greenhouse gases in the atmosphere due to human activities are most likely the underlying cause of warming in the 20th century. The exact value of the temperature rise is not the most important factor in coming to this conclusion, it is the trend. As is stated in this paper from which this graph was taken: Since the mid twentieth century the uncertainties in global and hemispheric mean temperatures are small, and the temperature increase greatly exceeds its uncertainty. In earlier periods the uncertainties are larger, but the temperature increase over the twentieth century is still significantly larger than its uncertainty.
Based on my conclusions, that global warming is real, and that greenhouse gases are the most important cause that we have any control over, I believe that all efforts to decrease carbon dioxide and methane emissions need to be taken, with more emphasis than we have been giving this effort. The length of this trend is also of some question to me, but the important thing is that it is happening and has been happening for over 100 years and there is no rational reason for it to stop. If for some reason these conclusions are wrong and there are some, in my opinion small uncertainties about global warming, we will have cost the world economies rather large amounts of money, but not in vain, because we have decreasing supplies of increasingly expensive fossil fuels and that the technologies that reduce global warming -- biofuels, better batteries, electric vehicles, and renewable energy -- also reduce our dependency on fossil fuels, an equally important problem. This dual concern is what caused me to create The Energy Blog.