Assertion (A): Attributing a particular rainfall event to seeding is generally impossible.
Reason (R): No counterfactual exists for the individual event in question.
Answer: A
Both are true and the reason gives the obstacle, and this affects litigation as much as science. Neither a claim of benefit nor one of harm can usually be substantiated. The missing counterfactual defeats both arguments.
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State whether the following is true or false.
There is an international convention prohibiting hostile use of environmental modification techniques.
Answer: B
The convention concluded in 1976 forbids environmental modification for military purposes. It arose from concern about attempts to modify weather during conflict. It remains the principal international instrument on the subject.
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Inadvertent weather modification refers to
Answer: C
Urban aerosol, ship exhaust and industrial emissions all alter clouds without any such intention. The effects are frequently larger than those any deliberate programme has demonstrated. The contrast is a standing irony of the field.
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Match each example of inadvertent modification with its cause.
List I
A. Ship tracks
B. Urban rainfall anomaly
C. Contrail cirrus
D. Reduced snowpack
List II
1. aircraft exhaust in ice supersaturated air
2. exhaust particles brightening marine cloud
3. soot deposition darkening the surface
4. aerosol and heat downwind of a city
Answer: D
Each is a documented effect of human activity on cloud or precipitation. None was intended, and several are larger than the effects deliberate seeding has been able to demonstrate. None of the four was intended by anyone.
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Assertion (A): Inadvertent modification may exceed deliberate modification in magnitude.
Reason (R): Industrial and transport aerosol acts continuously over vast areas.
Answer: A
Correct answer: Both A and R are true, and R is the correct explanation of A
Both are true and the reason gives the mechanism. Deliberate seeding treats particular clouds for a few hours; industrial and transport aerosol is emitted continuously over whole continents and alters the droplet population of clouds everywhere. The unintended effect is therefore very much the larger, though it was never designed.
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Three of the following are examples of inadvertent weather modification. Which is the odd one out?
Answer: B
Correct answer: silver iodide released from a ground generator
That is deliberate modification - the whole subject of the topic. The other three are unintended consequences of activity undertaken for other reasons: urban rainfall anomalies, ship tracks in marine stratocumulus, and contrail cirrus, each a real modification nobody set out to make.
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Marine cloud brightening as a geoengineering proposal would involve
Answer: C
More and smaller droplets raise the albedo of marine stratocumulus by the Twomey effect. It is proposed as a regionally targeted intervention rather than a global one. It acts through cloud rather than directly on sunlight.
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Consider the following statements about marine cloud brightening.
1. It exploits the first indirect aerosol effect.
2. It would need continuous operation to sustain any cooling.
3. Its effects would persist for centuries once begun.
Answer: D
The first two are correct and follow from the short aerosol lifetime. The third is wrong, since cessation would restore the previous state within days rather than centuries. Sea salt is removed from the air very quickly.
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Assertion (A): Marine cloud brightening would have to be sustained continuously to have any effect.
Reason (R): Sea salt aerosol is removed from the atmosphere within days of release.
Answer: A
Both are true and the reason gives the short residence time, and stopping would end the cooling almost at once. This termination behaviour is a central objection to such proposals. Termination shock is the standard term for the concern.
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Cirrus thinning has been proposed as a means of
Answer: B
Thin cirrus warms the surface by trapping outgoing infrared more than it reflects sunlight. Seeding to reduce its coverage would therefore act on the longwave side of the energy budget. Most other proposals act on incoming sunlight instead.
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