Page 310 - Earth's Climate Past and Future

286 PART V • Historical and Future Climate Change

Years ago Years ago
15,000 10,000 5,000 0 15,000 10,000 5,000 0
300

290
700
280
CO 2 (ppm ) 270 CH 4 (ppb ) 600

260

250
Stage 1 Stage 1
Stage 5 500 Stage 5
240 Stage 7 Stage 7
Stage 9
Stage 9
230 Stage 11 Stage 11
15,000 10,000 5,000 0
15,000 10,000 5,000 0 Years before Pmin Pmin
Pmin
Years before Pmin
FIGURE 15-14 Wrong-way CO and CH trends Atmospheric concentrations of CO and
2 4 2
CH , which fell during the early stages of previous interglaciations, instead rose during the
4
current one. (Adapted from W. F. Ruddiman, “The Anthropogenic Greenhouse Era Began Thousands
of Years Ago,” Climatic Change 61 [2003]: 261–93.)

cores show the spread of agriculture from its place Initially, farming occurred in small clearings, but by
of origin in the Fertile Crescent to adjacent regions 2000 years ago, large parts of China, Southern Europe,
(Figure 15–15). Clearance of forests in southeast Europe and India had already been deforested. A survey of
began just after 8000 years ago, the same time that the England in 1086 (the Domesday Book) found that 85%
CO curve began its anomalous rise. By the start of the of the arable land was in pasture or crops, with only
2
Bronze Age, 5500 years ago, agriculture had spread into 15% still in forest. This gradual clearance of Eurasian
virtually every part of Europe where farming is prac- forests contributed to the slow rise in CO concentra-
2
ticed today. Deforestation was also underway in China tions over the last 8000 years.
and India during this same interval. Whether the trees The methane concentration began its anomalous
were burned or left to rot, CO was delivered to the rise somewhat later, near 5000 years ago (see Figure
2
atmosphere. 15–14). This increase could not have come from tropical

>10,000 years ago
10,000–9000
9000–7800
7800–6800
6800–5700

FIGURE 15-15 The spread of agriculture The practice
of agriculture originated in the region north and east of
the Mediterranean and gradually spread into Europe,
North Africa, and other parts of Asia. (Adapted from N.
Roberts, The Holocene, 2nd ed. [Oxford: Blackwell, 1998].)