Although these molecules allow radiation at visible wavelengths, where most of the energy of sunlight is concentrated,to pass through,they absorb some of the longer-wavelength,infrared emissions radiated from the Earth's surface,radiation that would　otherwise be transmitted back into space. (4)

雖然這些分子允許可見波長(visible wavelength)的輻射——陽光的絕大部分能量就匯集于此——不受阻擋地穿透，但它們卻會(huì)吸收某些較長波長(longer- wavelength)，亦即從地球表面輻射出的紅外發(fā)射(infrared emission)，這種輻射若不是二氧化碳的緣故就會(huì)被重新輸送回太空。

難句類型：

復(fù)雜修飾、抽象詞

解釋：

前面的分句中有一個(gè)不算很長的插入語，但是因?yàn)樗迦氲奈恢谜迷诠潭ù钆鋋llow something to do somthing中間，將allow和to分得很遠(yuǎn)，所以讀起來讓人感覺很不舒服。

后面的分句中的最后一行radiation that would otherwise be transmitted back into space是其前面的infrared emissions的同位語。其中的otherwise是副詞作狀語，表示如果后面的分句所說的they absorb some of the longer-waverlength, infrared emissions不發(fā)生時(shí)的后果。

意群訓(xùn)練：

Although these molecules allow radiation at visible wavelengths, where most of the energy of sunlight is concentrated, to pass through, they absorb some of the longer-wavelength， infrared emissions radiated from the Earth's surface,radiation that would　otherwise be transmitted back into space.