I ran into a sentence that’s easy to misunderstand even though it’s written “correctly.”
Here’s the sentence:
Ocean temperatures are also much less variable than surface temperatures, which can swing greatly from year to year, and therefore give a clearer signal of global warming.
What is the subject of “gives the clearer signal of global warming”? Is it surface temperatures or ocean temperatures? Put another way, what does the “therefore” refer to, the “swing greatly” or the “much less variable”?
“Surface temperatures” and “swing greatly” are both closer to the “therefore give,” so that’s what the clause should refer to, right? Nope!
I think the writer of this article, Nicholas Kusnetz, (and maybe his editor) are so familiar with the mechanics of the topic that they assumed the readers would already know that the more stable temperatures are better indicators of change.
They expected the readers to jump over two wrong answers to get to the correct reference, a serious mental jolt. Mental jolts are not good. The sentence should have ended:
… and therefore ocean temperatures give a clearer signal of global warming.
Now the reader can’t get it wrong. And that’s how you should write!
PS—I like to include pictures in this blog when I can, so here’s one from the article. Notice that it describes ocean temps, not air temps.: