We don’t need to wait until the average global temperature trend is unequivocally down. It is trivially easy for anyone with access to existing CO2 and temperature measurement data-sets to falsify the statement that CO2 (at any level that ever existed) causes significant warming.
If CO2 is a forcing, a scale factor times average CO2 level times the duration divided by the effective thermal capacitance (consistent units) equals the temperature change of the duration. During previous glaciations and interglacials (as so dramatically presented in An Inconvenient Truth) CO2 and temperature went up and down nearly together. This is impossible if CO2 is a significant forcing so this actually proves CO2 CHANGE DOES NOT CAUSE SIGNIFICANT CLIMATE CHANGE.
See more on this and discover the two factors that do cause climate change (95% correlation since before 1900) at http://agwunveiled.blogspot.com . The two factors which explain the last 300+ years of climate change are also identified in a peer reviewed paper published in Energy and Environment, vol. 25, No. 8, 1455-1471.