Which of the following gases does NOT contribute to global warming?

The correct choice is helium, as this gas does not contribute to global warming. Helium is an inert, non-reactive noble gas that exists in the atmosphere in trace amounts. It does not absorb heat radiation from the Earth's surface or interact with infrared radiation, which are key processes that contribute to the greenhouse effect and global warming.

In contrast, carbon dioxide, water vapor, and ozone are all considered greenhouse gases. Carbon dioxide traps heat in the atmosphere and is a significant contributor to global warming, primarily due to human activities like burning fossil fuels. Water vapor is the most abundant greenhouse gas and plays a crucial role in the natural greenhouse effect, as it can hold heat in the atmosphere. Ozone, particularly in the troposphere, has warming effects due to its ability to absorb ultraviolet radiation and convert it into heat.

Thus, helium stands out as a gas that does not play a role in the processes that lead to global warming.