  The IPCC AR6 assessment of the impacts and risks associated with projected
climate changes for the 21st century is both alarming and ambiguous. According
to computer projections, the global surface may warm from 1.3 to 8.0 {\deg}C by
2100, depending on the global climate model (GCM) and the shared socioeconomic
pathway (SSP) scenario used for the simulations. However a substantial number
of CMIP6 GCMs run "too hot" because they appear to be too sensitive to
radiative forcing, and that the high/extreme emission scenarios SSP3-7.0 and
SSP5-8.5 must be rejected because judged to be "unlikely" and "highly
unlikely", respectively. This paper examines the impacts and risks of
"realistic" climate change projections for the 21st century generated by
assessing the theoretical models and integrating them with the existing
empirical knowledge on global warming and the various natural cycles of climate
change that have been recorded by a variety of scientists and historians. This
is achieved by combining the "realistic" SSP2-4.5 scenario and empirically
optimized climate modeling. The obtained climate projections show that the
expected global surface warming for the 21st century will likely be mild, that
is, no more than 2.5-3.0 {\deg}C and, on average, likely below the 2.0 {\deg}C
threshold. This should allow for the mitigation and management of the most
dangerous climate-change-related hazards through appropriate low-cost
adaptation policies. In conclusion, enforcing expensive decarbonization and
net-zero emission scenarios, such as SSP1-2.6, is not required because the
Paris Agreement temperature target of keeping global warming below 2 {\deg}C
throughout the 21st century should be compatible also with moderate and
pragmatic shared socioeconomic pathways such as the SSP2-4.5.
