Scientists studying the effect of large volcanic eruptions on global climate have long foc

Scientists studying the effect of large volcanic eruptions on global climate

have long focused on the major quantities of carbon dioxide (C02), a gas known

to contribute to the greenhouse effect, produced by these eruptions. It is well

observed that such greenhouse gases trap heat radiated from the surface of the

(5) earth, thereby forming a type of insulation around the planet. The greenhouse

effect is essential for ecological equipoise because it maintains the temperature

of the planet within habitable parameters, but there is growing concern that

man-made production of gases such as CO[,2] from the burning of fossil fuels may

be threatening the system's tolerance, and have resulted in excessive warming

(10) on a global scale.

While volcanic eruptions indubitably metabolize and accumulate C0[,2] in the

atmosphere, it has been recently discovered that their impact is virtually trivial

compared to the quantity produced by human activities, especially heavy

industry. In reality, the more substantive climatic effect from volcanoes results

(15) from the production of atmospheric haze, whereby large eruption columns inject

ash particles and sulfur-rich gases into the troposphere and stratosphere, clouds

that circumscribe the globe within weeks of the volcanic activity. Ash and

aerosol clouds from large volcanic eruptions disseminate quickly through the

atmosphere, and the small ash particles decrease the amount of sunlight

(20) reaching the surface of the earth and lower average global temperatures, while

the sulfurous gases combine with water in the atmosphere to form. acidic

aerosols that also absorb incoming solar radiation and scatter it back out into

space.

There is evidence that volcanoes' stratospheric ash clouds has a lesser

(25) effect on global temperatures than aerosol clouds, given that the major Mt. St.

Helens eruption had lowered global temperatures by about 0.1 degree C, while

two years later the much smaller eruption of El Chico had, by contrast, three to

five times the global cooling effect worldwide. Despite its smaller ash cloud, El

Chico emitted more than 40 times the volume of sulfur-rich gases produced by

(30) Mt. St. Helens, revealing that the formation of atmospheric sulfur aerosols has

a more substantial effect on global temperatures than simply the volume of ash

produced during an eruption. Sulfate aerosols appear to necessitate several

years to settle out of the atmosphere, one of the reasons their effects are so I

widespread and enduring. This corroborates the opinion of those scientists who

(35) argue that without the cooling effect of major volcanic eruptions such as El

Chico, global warming effects caused by human activities would be far more

substantial. It should be noted that major volcanic eruptions have additional

climatic effects beyond global temperature decreases and acid rain, for ash and

aerosol particles suspended in the atmosphere scatter light of red wavelengths,

(40) often resulting in brilliantly colored sunsets and sunrises around the world.

According to the passage, scientists have decided that sulfur aerosols from volcanic eruptions affect global temperatures to a greater extent than ash clouds because

A．the greenhouse gas effect produced by human activities tends to have a much greater environmental effect than that of volcanic explosions

B．clouds of sulfur-rich gases tend to achieve greater heights in the stratosphere than do ash clouds

C．a particular explosion producing high sulfur and little ash had a greater environmental effect than the converse

D．the burning of fossil fuels tends to exacerbate the effects of sulfurous aerosols, but not those of ash clouds

E．global warming effects tend to minimize the impact of ash clouds, but not those of sulfurous aerosols