Scientists have discovered that for the last 160,000 years, at least, there has ) F0 S/ U8 p: j" y
been a consistent relationship between the amount of carbon dioxide in the air and # N! U! s2 C" |
the average temperature of the planet. The importance of carbon dioxide in , i, r3 m, f1 W& z, Y8 R
regulating the Earth's temperature was confirmed by scientists working in eastern
) b2 X- E! \5 s9 D- ^8 \(5) Antarctica. Drilling down into a glacier, they extracted a mile-long cylinder of ice % P) d- o- E3 n2 S
from the hole. The glacier had formed as layer upon layer of snow accumulated year 9 { F. j Q4 v6 Y; }) H* s
after year. Thus drilling into the ice was tantamount to drilling back through time.
) f6 I/ A7 a+ M; R. v; G" f7 YThe deepest sections of the core are composed of water that fell as snow ) a# d9 V+ }4 A! t- s' W. s
160,000 years ago. Scientists in Grenoble, France, fractured portions of the core and
5 O1 p; `3 _; B( @. o(10)measured the composition of ancient air released from bubbles in the ice. 9 s# R5 Q2 p" l2 y# Z6 q
Instruments were used to measure the ratio of certain isotopes in the frozen water to 2 j; J7 W, G4 j9 v6 [$ P
get an idea of the prevailing atmospheric temperature at the time when that
3 w! X) u4 n& j! ^/ jparticular bit of water became locked in the glacier. . [4 d9 _/ ^9 \
The result is a remarkable unbroken record of temperature and of atmospheric
& E4 W* s" Y3 Q+ a9 ?: I(15)levels of carbon dioxide. Almost every time the chill of an ice age descended on the
- t: o) Q* Z' E1 d, ]8 @0 Fplanet, carbon dioxide levels dropped. When the global temperature dropped 9°F (5 °C),
! B7 X: e7 B3 v/ z$ _carbon dioxide levels dropped to 190 parts per million or so. Generally, as each
$ X3 n6 O& s- B& X, `+ Sice age ended and the Earth basked in a warm interglacial period, carbon dioxide 7 G6 R& a( P& A- @5 |
levels were around 280 parts per million. Through the 160,000 years of that ice ; Z7 x1 `" O0 y1 Q) M3 d I- f
(20)record, the level of carbon dioxide in the atmosphere fluctuated between 190 and
# _8 H6 U' F/ i' C: c280 parts per million, but never rose much higher-until the Industrial Revolution $ i, z8 x7 j7 |! r5 G2 A
beginning in the eighteenth century and continuing today.
, }& s9 L+ Y) O* M8 Y bThere is indirect evidence that the link between carbon dioxide levels and ! ~' `) Q7 C# O& q5 d
global temperature change goes back much further than the glacial record. Carbon . b% h6 w6 |# g
(25) dioxide levels may have been much greater than the current concentration during the
. i/ j% Y: _$ I9 |' @& m Carboniferous period, 360 to 285 million years ago. The period was named for a
7 o3 i6 E* i) M* R4 e a4 X$ r, {profusion of plant life whose buried remains produced a large fraction of the coal
+ d' Y: q1 p& D0 t' cdeposits that are being brought to the surface and burned today. |
发表于 2012-8-14 22:34:35
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