0 A very brief introduction

Climate variability results from a very diverse set of physical phenomena and occurs on a very wide range of time scales. It is difficult to envision a single model, complex as it might be, which could explain, simulate or predict all sources of climate variability. It is therefore simple models, that concentrate on a single or a few phenomena and on some limited range of time scales, that have had the most success in explaining the physics of climate variability. We start these lectures with a very brief gallery of examples of climate variability from very long time scales to shorter ones, and of a few climate toy models that are displayed without much of a discussion, as an introduction to the fuller review in the following lectures. After this introduction, the following lectures discuss conceptual (toy) models of the El Nino Southern Oscillation phenomenon (lectures 1-3), of the thermohaline circulation (lectures 4-5), and of glacial cycles (lectures 8-9) preceded by some basic concepts of climate dynamics (lectures 6-7). We conclude with a brief discussion of toy models of very early earth and planetary climates (lecture 10). Climate variability exists on all time scales from seconds to billions of years, as shown in the schematic spectrum of Fig. 1. The last 60 Million years (Myr) show a gradual slow cooling, and a strong increase in variability over the past few millions of years (Fig. 2). Continuing to the more recent past, the Quaternary (last 2.6 Myr) glaciation record shows the glacial cycles and a significant change in the nature of these oscillations some 1 Myr ago (Fig. 3). Focusing on the past 150,000 years, one sees a full glacial cycle (Fig. 4). On shorter-yet time scales, and focusing on the past 90 kyr or so, we can see Heinrich events (major iceberg discharges on a 7-10 kyr time scale), and Dansgaard-Oeschger oscillations (warm events in Greenland ice core records, 1000-1500 yr time scale, Fig. 5). The variability is clearly very dramatic in terms of both amplitude and abruptness of the observed climate changes. A record of the past 10,000 yr shows the Younger Dryas cold event interrupting the last deglaciation (Fig. 6), while the record during the past 500 years shows the “little ice age” (Fig. 7). Finally, on a time scale of a few years to decades, we see the North Atlantic Oscillation record (Fig. 8) and an El Nino record for the past 50 years (Fig. 9).