3
Comprehension: (86-90)
Read the following information carefully and answer the given questions.
While greenhouse gases are warming Earth's surface, they’re also causing rapid cooling far above us, at the edge of space. In fact, the upper atmosphere about 90km above Antarctica is cooling at a rate ten times faster than the average warming at the planet's surface. Our new research has precisely measured this cooling rate and revealed an important discovery: a new four-year temperature cycle in the polar atmosphere. The results, based on 24 years of continuous measurements by Australian scientists in Antarctica, were published in two papers this month.
The findings show Earth's upper atmosphere, in a region called the ''mesosphere'', is extremely sensitive to rising greenhouse gas concentrations. This provides a new opportunity to monitor how well government interventions to reduce emissions are working. Since the 1990s, scientists at Australia's Davis research station have taken more than 600,000 measurements of the temperatures in the upper atmosphere above Antarctica. Weve done this using sensitive optical instruments called spectrometers.
These instruments analyse the infrared glow radiating from so-called hydroxyl molecules, which exist in a thin layer about 87km above Earths surface. This “airglow” allows us to measure the temperature in this part of the atmosphere.
Our results show that in the high atmosphere above Antarctica, carbon dioxide and other greenhouse gases do not have the warming effect they do in the lower atmosphere (by colliding with other molecules). Instead, the excess energy is radiated to space, causing a cooling effect.
Our new research more accurately determines this cooling rate. Over 24 years, the upper atmosphere temperature has cooled by about 3℃, or 1.2℃ per decade. That is about ten times greater than the average warming in the lower atmosphere – about 1.3℃ over the past century.
Our project also monitors the spectacular natural phenomenon known as ''noctilucent'' or ''night-shining'' clouds. While beautiful, the more frequent occurrence of these clouds is considered a bad sign for climate change. Our research also monitors how cooling temperatures are affecting the occurrence of noctilucent clouds. There is already some evidence the clouds are becoming brighter and more widespread in the Northern Hemisphere. Hence, long term monitoring is important to
The noctilucent clouds are becoming brighter and more widespread in the :
