The cooling oceans

CAE Use of English Part 3: WORD FORMATION EXERCISE 1

Use the word in capitals to form a word that best fits each gap, then press "Check" to check your answers.
The upper layers of Earth's oceans have cooled (0) significantly SIGNIFY over the past two years, even though the planet as a whole is warming up. While this may just be part of he natural (1) VARY
of oceans, climatologists are still confounded by the massive unaccountable loss of heat.
Scientists have been (2) INCREASE concerned by rising sea temperatures over the last 50 years but these new (3) FIND tell a different story.
Generally speaking, the (4) ABSORB of heat by the oceans reduces atmospheric warming. Now (5) MEASURE taken by the National Oceanic and Atmospheric Administration have put a wrinkle in the trend. The researchers used data from 3000 floating buoys which monitor the oceans (6) WORLD.
They found that the oceans dropped in temperature by an (7) BELIEVE 0.02 degrees centigrade between 2011 and 2013.
Now, that may not seem like much, but trying to account for the missing energy is proving to be enormously (8) PROBLEM. lt is possible that volcanic eruptions are one main cause of the phenomenon, but no firm answers have yet been provided.