毎年、２７００万エーカーの熱帯雨林が破壊されているのである。

、。

Every year, 27 million acres of tropical rainforest are being destroyed.

Literal

Every-year, 27-million acres [possessive-の] tropical-rainforest [subject-が] is-being-destroyed [explanatory-のである].

のである adds explanatory emphasis — presenting this as a fact the reader should take note of, not just reporting it neutrally. 破壊されている uses passive + ている for an ongoing process: the destruction is continuous. ２７００万 uses 万 (ten thousand) as the counting unit — 2700万 = 27 million.