The climate sensitivity to a doubling of CO2 with feedbacks may only be about 1°C, with humans contributing just 30% to the global warming since 1850.

New research indicates the climate models that the Intergovernmental Panel on Climate Change (IPCC) rely upon for policy-making – and to claim humans are 100% responsible for the warming since 1850 – are fundamentally flawed.

The models cannot reproduce natural climate variability, nor can they simulate the positive water vapor and cloud feedback assumptions essential to demonstrably amplifying the warming thought incur from doubling CO2.

The assumptions about total solar irradiance (TSI), and/or solar impacts on cloud formation and cosmic rays  IPCC chooses to emphasize may underestimate the role of solar forcing in climate change five-fold.

Key points in Dr. Scafetta’s research summary include:

• Equilibrium Climate Sensitivity (ECS) estimates for doubled CO2 (280 to 560 ppm) plus feedbacks may be 1°C (0.7°C to 1.3°C) due to the lack of positive feedback from water vapor and clouds.

• The climate may be 4 to 6 times more sensitive to solar forcing factors (not just TSI alone) than presumed by models of radiative forcing.

• Human activity may only explain about 30% of the global warming since 1850, with warm biases in the land surface record explaining 20% and natural solar-induced variability factors explaining 50%.

• Variations in cloud albedo from 1983 to 2010 may explain 0.4°C of the global warming during this period.

Image Source: Scafetta, 2026