Here the temperatures obtained from models and different proxies can vary by more than 20 ∘C. We focus on the mid-Pliocene warm period (mPWP) and show that understanding the northern high-latitude terrestrial temperatures is particularly difficult for the coldest months. Both models and data indicate an amplified warming of the high latitudes during the Pliocene however, terrestrial data suggest that Pliocene northern high-latitude temperatures were much higher than can be simulated by models. Reconciling palaeodata with model simulations of the Pliocene climate is essential for understanding a world with atmospheric CO 2 concentration near 400 ppmv (parts per million by volume).
