Based on the increase of solar activity during the twentieth century, it should account for between half to two-thirds of all climate change
Averaged over the complete solar cycle, there’s been minimal long-term change in the Sun’s overall brightness since the start of the Industrial Revolution. Records of sunspots show increased solar activity during the first 7 decades of the 20th century, likely tied to the peak of the last 100-year Gleissberg Cycle. Following that peak around 1960, solar activity declined. In fact, activity during the most recent solar cycle is among the lowest in a century. Meanwhile, the rate of global warming has accelerated over the past few decades. [...] Taken together, the increasing solar activity of the first half of the 20th century and the decreasing activity since then have largely canceled each other out in terms of their influence on global temperature. In the Sixth Assessment Report from the Intergovernmental Panel on Climate Change, experts concluded that the best estimate for the influence of the Sun on climate between the pre-industrial (1850-1900) and the present (2010-2019) was that it added 0.01 Watts per square meter to the global energy imbalance causing global warming. Such a small energy imbalance (scientists call it a radiative forcing) is likely to be responsible for no more than 0.01 degrees Celsius of warming over that period. That’s 100 times smaller than the overall warming that’s occurred on Earth over the industrial period, which the IPCC estimates as 0.95–1.2 degrees Celsius in 2011–2020 versus 1850–1900.