Page 331 - Earth's Climate Past and Future

CHAPTER 16 • Climate Changes During the Last 1000 Years 307

A 0 FIGURE 16-17 Effect of
pandemics on atmospheric CO
2
Mortality caused by pandemics led
–1 –2
to farm abandonment, reforestation,
Δ CO 2 (ppm) –2 Reforestation –4 GtC trees. The two parts of the figure
and storage of carbon in growing
show a simulation of carbon
sequestered by reforestation and
–6
–3
Combined signal
related effects from the American
pandemic (1500–1700), indicating a
–4 reduction of atmospheric CO half
2
as large as that measured in ice cores
0 500 1000 1500 2000
(Law and Taylor Domes).
Year
B 285

~2ppm

~5ppm

CO 2 (ppm) 280 ~2ppm

? ? ?

275 Taylor Dome Law Dome

2000 1500 1000 500 0
~ Years Ago

“early anthropogenic hypothesis” summarized in Chap- (2) the American pandemic, a host of diseases carried by
ter 15 was grounded in the assumption that deforesta- Europeans that killed some 50 million Native Americans
tion by humans, aided by feedbacks from the climate between 1492 and 1700, or 85–90% of the previous
system, caused the slow increase in the amount of population. At the times these pandemics occurred,
atmospheric CO during the last 8000 years (see Figure many Europeans and most Native Americans farmed
2
15–14). From this point of view, any subsequent drop in areas in clearings cut into natural forests. When the pan-
the rising CO trend could have had an origin con- demics decimated the populations, the forests grew back
2
nected in some way to humans. in fields left untended, and the carbon required by these
Two great pandemics occurred during the interval of growing trees for photosynthesis was taken from the
falling CO values: (1) the “Black Death,” an outbreak of CO in the atmosphere (as well as the surface ocean and
2 2
bubonic plague between 1347 and 1352 that killed 25 the biosphere elsewhere on Earth). Much of the refor-
million Europeans, ~33% of the population at that time; estation took place within 50 to 100 years.