Howard Lee, Ars Technica :

Confusing matters further, the Miocene world started out different from today. The early Miocene climate was warmer than our preindustrial climate, grasslands had not yet proliferated, and the oceans were connected differently, with a current flowing from the Pacific to the Atlantic through what is now Panama, while the Bering Strait was closed. Yet scientists think the currents probably didn’t have much of an effect on the climate, and in many other ways the planet was quite similar to today.

So there are big uncertainties in how well the Miocene represents our descendants’ future. It’s also true that there is no analog for the rapid rate of modern emissions in at least the last 66 million years. You could reasonably dismiss the relevance of any ancient analog on those grounds. But bear in mind that uncertainty is a double-edged sword: it cuts both ways, not only in the comforting direction.

Nous pouvons comparer la concentration en CO2 dans notre atmosphère contemporaine à la concentration en CO2 estimée dans l’atmosphère du Miocène, mais nous ne pouvons pas en déduire que nous nous dirigeons vers un climat semblable à celui qui gouvernait la planète il y a 16 millions d’années. L’incroyable augmentation des concentrations en gaz à effet de serre est un événement inédit : la température va continuer d’augmenter, mais il est impossible de prévoir l’ampleur de cette augmentation et ses conséquences sur la planète, une réalité aussi terrifiante que passionnante.