What are the harmful effects arising from the greenhouse effect?
Increasing greenhouse gas emissions from human activities are trapping more energy (due to the greenhouse effect) on earth leading to several negative effects.
The greenhouse effect itself is not inherently bad. It is the rapid increase in greenhouse gas (GHG) emissions from human activities that are causing problems. GHGs are trapping more energy (due to the greenhouse effect) on earth leading to several negative effects all connected to global warming (see image below). As more solar energy is trapped on earth, the planet warms and this warming is happening at a rapid pace.
You can read about how greenhouse gases are connected to global warming here. Global warming is causing a multitude of negative effects. See these related questions on Socratic: how will global warming affect humans, how does global warming effect animals and their habitats, and what are the possible consequences of a warmer Earth.