In Hadley GustinâÄôs Dec. 7 column on the importance of water, she comments, âÄúas the global population continues to grow exponentially âĦâÄù Excuse me, but please learn what âÄúexponentialâÄù means. The world population growth rate has been declining toward replacement for decades, and although there has been a recent bump, the rate is expected to begin declining again next year. The United Nations has been revising their population estimates downward since the late 1990s as global fertility rates decline more rapidly than previously expected. We need to help less developed countries move away from a subsistence lifestyle where many children are considered a necessity.