Since ClimateGate put the Climate Cabal on their back heels, a flood of new science has emerged, no longer being suppressed by the cabal, generally challenging the anthropogenic (man-made) global warming case. A simple rebuttal to man-made global warming is that the increase in Co2 has not had a corresponding increase in the greenhouse effect.
A former NASA contractor, Dr. Ferenc Miskolczi, posited such a rebuttal based on his independent research. This chart shows that there has been no significant increase in the greenhouse effect for the past 60 years:
The black line is the annual variation in atmospheric "aborbing power" over a 61-year period. The red trend line shows the greenhouse absorbing power remaining constant (in equilibrium) during that period. Greenhouse absorption increases (blue trend line) only when H20 levels are kept constant.
The implication is that nature has a way of self-regulating.
One of the core assumptions of the global warming case is that an increase in Co2 should be amplified by other greenhouse gases, notably water vapor, but instead we have seen a decrease in water vapor where there is an increase of Co2. The red line in the chart is the greenhouse absorbing power, which is essentially flat for the period. The blue line is how the red would have looked if water vapor had remained constant. The global warming models all assume that water vapor would increase, steepening that blue line, but the opposite happened, disproving their theory.