19. Dr. Myers and Dr. Worm argue that their work gives a correct baseline, which future management efforts must take into account.

【分析】多重复合句。句子主干为Dr. Myers and Dr. Worm argue that, that引导宾语从句。宾语从句中又含有which引导的定语从句修饰先行词baseline。定语从句中 which 作take的宾语,构成 take sth. into account。
【译文】迈尔斯博士和沃尔姆傅士指出他们的工作给出了一个正确的基线,未来的管理工作必须对此加以考虑。
【点拨】take sth. into account“考虑到…”。此外，相同意义的表达还有 take sth. into consideration;allowing for sth. ; in view of sth. ; have sth. in mind 等。

20. The notion is that people have failed to detect the massive changes which have happened in the ocean because they have been looking back only a relatively short time into the past.

【分析】多重复合句。本句中含有三个从句。首先, that引导的表语从句；其次是which引导的定语从句，修饰先行词changes;最后是由because引导的原因状语从句。
【译文】这个想法认为人们无法测定海洋中的大规模变化，因为他们仅仅考虑了一段相对较近的历史。