Cool tropics paradox

The cool tropics paradox. The geological evidence appeared to constrain temperatures to the red/blue band, whereas models produced the brown line taking just continental configuration into account, and the blue line when they included increased atmospheric CO2. Vertical axis: Temperature; horizontal:latitude.

The cool tropics paradox is the apparent difference between modeled estimates of tropical temperatures during warm, ice-free periods of the Cretaceous and Eocene, and the colder temperatures which proxies suggested were present. The long-standing paradox was resolved when novel proxy derived temperatures showed significantly warmer tropics during past greenhouse climates. The low-gradient problem, i.e. the very warm polar regions with respect to present day, is still an issue for state-of-the-art climate models.