One of the reasons that you can’t just use historical trends in data over time to predict future climate is that there are often feedback loops that amplify the changes in temperature that may occur in the future. One of these feedback loops is the change in albedo (reflectance of sunlight) due to melting of snow and ice in the Arctic and replacing the land surface with dark soil or dark ocean water, which can change the energy balance in the region.
Another one is the impact of melting permafrost in both the Arctic and Antarctic (although the Arctic has a lot more because there is more land in the Northern Hemisphere than the Southern Hemisphere). The melting of permafrost allows the plant debris trapped there to decay, releasing carbon dioxide to the atmosphere, which accelerates the warming. You can read more about this at EarthSky here.