Nonlinear effects occur when a change in one variable does not produce a proportional change in another variable. This means that small changes can lead to large impacts, or vice versa, depending on the system involved. For example, in climate change, a slight increase in temperature can lead to significant shifts in weather patterns, illustrating how interconnected systems can behave unpredictably. In physics, nonlinear effects are often observed in systems like chaos theory, where small differences in initial conditions can result in vastly different outcomes. This unpredictability makes it challenging to forecast behaviors in complex systems, such as ecosystems or economies, where multiple factors interact in intricate ways.