Long-term trends in ambient noise levels.

Abstract

This paper addresses the subject of long‐term trends in ambient noise levels, a topic of great interest to both the scientific community and the general public. This attention stems primarily from concerns over the effects of apparently increasing sound levels on marine mammals. A growing, though limited, body of literature suggests that low‐frequency noise levels increased approximately 15 dB during the period 1950–2000, an amount that corresponds to about 3 dB/decade. One hypothesis states that this increase is predominantly anthropogenic in nature and can be attributed to increased commercial shipping activity, which, in turn, can be linked to global economic growth. As a result, a direct correlation may be drawn between ambient noise levels and the behavior of the global economy. This special session addresses an additional consequence of global economic activity, namely, increased ocean acidification leading to decreased absorption and therefore to increases in ambient noise levels associated with distant shipping. This paper also suggests topics of considerable interest for future research including (1) the relative contributions of commercial shipping activity versus ocean acidification to ambient noise levels and (2) the effect of the current economic downturn on noise levels. [Work supported by ONR.]