The objective of the Kyoto Protocol is to reduce greenhouse gas emissions. This international agreement, adopted in 1997, aims to combat climate change by setting binding targets for industrialized countries to reduce their emissions of greenhouse gases. Option 1, abolishing child labor, is not related to the Kyoto Protocol`s objective. Option 2, eliminating nuclear weapons, is also not directly related to the objective of the Kyoto Protocol. Option 3, increasing groundwater levels, is unrelated as well. Therefore, the correct answer is option 4, to reduce greenhouse gases. It is important to note that while the provided answer is generally correct, it is essential to understand that the Kyoto Protocol specifically targets greenhouse gas emissions and not just any kind of pollution or environmental issue.