The Present in the
Bosom of the Past
The first question many people ask about the issue of humaninduced climate change is how the forecast stacks up against natural variability and cycles in climate. Is global warming something big, or is it just nature–as–usual for the Earth? That question can now be answered by comparing the global warming forecast from Chapter 3 with past climate variations described in Chapters 4, 5, and 6. Even if you glazed over some of the marvelous details in those chapters, you should be able to jump back in here, reading this chapter as a sort of summary.
The impression I have is that global warming so far has been comparable to climate changes over the past millennium such as the Little Ice Age and the Medieval Optimum. In both cases, there have been regions where the climate changes are or were noticeable and harmful, but globally the impacts of the changes were subtle.
The potential climate change in the future is not subtle. If humankind burns all of the coal, the new climate of the Earth could be the warmest in tens of millions of years, since long before our evolution as a species. The transition from the natural climate to the new one could be the most severe global change