We should pause and make a point or two about these temperature reconstructions because they are very important to our understanding of how Earth's climate has been changing.
- The temperature reconstructions from multiple proxies (Fig. 2.2.13) compare well with the instrumental record — this gives us a basis for thinking that the reconstructions are reliable. They are also in good agreement with the temperature reconstructed from borehole data — this gives us even more confidence in the multi-proxy reconstruction.
- What we see is a very dramatic warming that begins around 1900 — the blade of the "Hockey Stick" — that is far larger in magnitude and far more abrupt than any climate change we see in the reconstructed climate history.
- The recent warming does not appear to be part of a cycle — if it were part of a cycle, then we should expect to see a similar abrupt large cooling that preceded the warming, but nothing of the sort appears in the record.