Solar irradiance and climate forcing in the near future

Annual levels of the Sun's irradiance are estimated until 2018 using parameterizations of the 10.7 cm radio flux. Peak irradiance during solar cycle 24 occurs in 2010, with levels comparable to or slightly lower than prior maxima in 2000, 1989 and 1981. Minima occur in 2006 and 2016. Future irradiance trends underlying the 11-year cycle, which are assumed not to exceed those in historical reconstructions during the past 350 years, are estimated to be less than +/-0.4 Wm(-2) per decade for total irradiance, +/-0.01 Wm(-2) per decade for UV radiation at 295-310 nm and +/-0.04 Wm(-2) per decade for UV radiation at 200-295 nm. When activity cycles and longer-term trend scenarios are combined, total solar irradiance forcing of climate between cycle minima in 1996 and 2016 is in the range +/-0.1 Wm(-2). For comparison, the forecast net anthropogenic climate forcing over this 22-year period is in the range 0.5 to 0.9 Wm(-2).