James Hansen's 1988 congressional testimony projected U.S. warming of 0.45°C by 2010 under moderate emissions, yet observed increases were about 0.3°C.
The predictions held up well. Hansen’s 1988 paper projected warming trends under three emission scenarios:
- A (high emissions) – ran hotter than observed.
- B (moderate, realistic) – tracked observed global warming closely.
- C (low emissions) – ran cooler than observed.
Later comparisons (e.g., Hausfather et al., 2019, Geophysical Research Letters) found that Hansen’s model produced nearly the correct warming rate once actual greenhouse gas concentrations were used as input.
The main difference came from emission assumptions, not from the physics of the model.