In the sentence "Water security is the gossamer that links together the web of food" (lines 1 and 2), the word "gossamer" can be correctly replaced by source with no difference in meaning.

The sentence "The volatility in food prices in 2008 should be treated as an early warning sign of what is to come." (lines 9 and 10) is in the passive voice. In the active voice, it can be written like this: As an early warning sign of what is to come should treat the volatility in food prices in 2008.

In the fragment "over the past 50 years or so" (lines 15 and 16), the expression "or so" means in an accurate manner.

In the sentence "This set of regional challenges becomes a fast-approaching global crisis" (lines 23 and 24), the word "crisis" is in its singular form. In fact, in its plural form, it will show the same spelling.

The word "stark", in the sentence "The financial crisis gives us a stark warning" (lines 42 and 43), implies that the financial crisis gives us a complete warning.