11on surface conditions (i.e., the air we breathe). There is no coordinated international
effort to limit future growth of tropospheric O 3. Human release of pollutants that lead
to formation of tropospheric aerosols causes climate to cool due to two processes
nearly equal in magnitude but having large uncertainty: the reflection of sunlight by
aerosols (Aerosol Direct Effect) and the effect of aerosols on cloud formation (Aerosol-
Cloud Interaction).^5 The net effect of all human activity on ΔRF (bar labeled Total
Anthropogenic) is about 25 % larger than ΔRF due to CO 2 and has a considerably
larger uncertainty (size of respective error bars) (Chap. 8, IPCC ( 2013 )).
Other aspects of global warming are represented in Fig. 1.4. The reflectivity of
Earth’s surface has changed primarily due to deforestation that makes the surface
(^5) The effect of anthropogenic aerosols on the radiative properties of clouds is different, from a cli-
mate modeling perspective, than the evolution of cloud properties as the surface warms. Specialists
refer to the former as the aerosol indirect effect and the latter as cloud feedback. A considerable
research effort informs us that the aerosol indirect effect leads to a cooling (negative RF) of uncer-
tain magnitude and the cloud feedback could either lead to warming or cooling.
Ozone
Well-mixed GHGs {
CO 2
Stratospheric Tropospheric
Stratospheric Water
Surface Albedo
Contrails
Land UseBlack Carbon on Snow
Total Aerosol {
Aerosol Direct E ect
Aerosol-Cloud Interaction
Total Anthropogenic
Human
Ac
tivities
Natural Processes
Radiative Forcing of Climate, 1750 to 2011
Solar Irradiance
Contrails + Induced Cirrus
H 2 O Vapor from CH 4
CH 4
∆RF Terms
∆RF (W m–2)
–1 012 3
N 2 OODS Other F-gases
Fig. 1.4 Radiative forcing of climate, various factors, Anthropocene. Change in radiative forcing
of climate (ΔRF) over the course of the Anthropocene (in this case, 1750–2011) due to human
factors (GHGs and aerosols) and natural processes (solar irradiance). Error bars represent the
5–95 % confidence interval. The ODS entry represents ΔRF due to ozone depleting substances
such as CFC-11, CFC-12, etc. The Other F-gases entry represents ΔRF due to HFCs, PFCs, SF 6 ,
and NF 3. Numerical estimates for ΔRF are shown when available; otherwise, numerical estimates
for the change in Effective Radiative Forcing (ΔERF) are used. After Fig. 8.15 of IPCC ( 2013 ).
See Methods for further information
1.2 The Anthropocene