He and colleagues compared sea ice conditions from 1987–1998 with those from 1999 to 2013.

他和同事将1987年至1998年的海冰状况与1999年至2013年的海冰状况进行了对比。

This is because four of the past five years have seen reasonably good ice conditions.

这是因为在过去的五年中，有四年的冰层状况相当好。

Officials say several years of poor ice conditions in areas around the colony led to the drowning of all newborn penguins beginning in 2016.

官员们表示，从2016年开始，该栖息地周围地区数年恶劣的冰雪条件导致所有新生企鹅溺水而亡。