Which two greenhouse gases have human activities significantly increased?

The two greenhouse gases that have seen significant increases due to human activities are carbon dioxide and methane.

Carbon dioxide is primarily released through the burning of fossil fuels for energy, deforestation, and various industrial processes. This increased concentration of carbon dioxide in the atmosphere is a major driver of climate change because it enhances the greenhouse effect, trapping more heat in the Earth's atmosphere.

Methane, on the other hand, is released from agricultural practices, particularly livestock digestion, as well as from landfills, natural gas extraction, and other industrial activities. Methane is much more effective at trapping heat than carbon dioxide, making its increase in the atmosphere particularly concerning for global warming.

The other pairs of gases listed, such as ozone and nitrogen dioxide, have different sources and are not primarily driven by greenhouse gas emissions from human activity in the same way. Water vapor is not directly increased by human activities; rather, it acts as a feedback mechanism in the climate system. Likewise, hydrogen sulfide and sulfur dioxide are more related to pollution and do not significantly contribute to the greenhouse effect in the way that carbon dioxide and methane do. This understanding of the sources and impacts of these gases highlights why carbon dioxide and methane are the correct answers in this context.