The greenhouse effect is where the temperature of the Earth increases. This happens as less heat is radiated back from the Earth than is received from the Sun.
The atmosphere becomes clogged up with "greenhouse gases" such as carbon dioxide from burning fossil fuels and methane. This lets the heat from the Sun in but stops some of it from be radiated back out again.
This is just how the glass on a greenhouse works. So the inside of the greenhouse gets warmer and warmer over time.
In the case of the Earth the warming up has happened very slowly over decades and centuries. However the levels of greenhouse gases have risen sharply recently.
As the temperature of the Earth increases it is predicted that we will see changes in weather patterns, including drought and flooding.
The Polar ice caps may melt and so produce raised sea levels. Low-lying areas will be flooded including many major cities.
Kristiina Tänav, Marek Hendrikson, 12D