The phrase "hurricane activity" refers to the occurrence, intensity, or behavior of hurricanes. It describes how many hurricanes are happening, how strong they are, and what they are doing. Full definition
It looks like there was a dramatic increase in hurricane activity in the 1996 - 2005 period (and to a lesser extent in the preceding 1986 - 1995 period). (globalwarmingsolved.com)
However, prior bouts of increased hurricane activity due to natural variation do not rule out a role for global warming the current period of increased activity since the early 1980s. (climatesignals.org)
The current study only looks at hurricane activity since 1970 — a relatively quiet period. (news.nationalgeographic.com)