Global Warming

60 Climates ofthe past

Satellites

Surface

Balloons

Satellites

Balloons

1960 1970 1980 1990 2000

Year

−1.0

−0.5

0.0

0.5

Anomaly (

°C)

(a)

1960 1970 1980 1990 2000

Year

− 4

− 2

0

2

Anomaly (

°C)

(b)

Agung El Chichon Pinatubo

Figure 4.2Time series of observations of global average temperature (◦C)

(relative to average for 1979–90) (a) for the lower troposphere based on

measurements from balloons and satellites compared with measurements at the

surface; (b) for the lower stratosphere from balloons and satellites.

them result from internal variations within the total climate system, for

instance between different parts of the ocean. (See Chapter 5 for more

details.)

The warming during the twentieth century has not been uniform

over the globe. For instance, the recent warming has been greatest over

Northern Hemisphere continents at mid to high latitudes. There have

also been areas of cooling, for instance over some parts of the

North Atlantic ocean associated with changes in ocean circulation (see

Chapter 5). Some of the recent regional patterns of temperature change

are related to different phases of atmosphere-ocean oscillations, such as

the North Atlantic Oscillation (NAO). The positive phase of the NAO,