The term "forcing agent" refers to any substance or process that causes a change in the environment, such as increasing greenhouse gas concentrations which force climate changes. Full definition
«Therefore, unless models miss effects of other forcing agents, it is likely that this [less efficient ocean heat uptake] process will occur and act to accelerate surface warming in coming decades.» (skepticalscience.com)
These basic scenarios and other forcing agents incorporated in the AOGCM projections, including several types of natural and anthropogenic aerosols, are discussed in Section 10.2.1. (ipcc.ch)
I think the most plausible route to getting a different result for the lapse rate trend is through the addition of other forcing agents, other than well - mixed greenhouse gases, acting near the tropopause. (gfdl.noaa.gov)