qDetection and attribution studies consistently
find evidence for
an anthropogenic signal in the climate record of the last 35 to 50 years.
qSimulations of the response to natural forcings
alone (i.e., the
response to variability in solar irradiance and volcanic eruptions) do not explain the warming in the
second half of the
20th century.
qHowever, they indicate that natural forcings may
have contributed to the
observed warming in the first half of the 20th century.
qMost of the observed warming over the last 50
years is likely to have been due
to the increase in greenhouse gas concentrations.