What is greenhouse effect? 

以下内容摘自wmo网站https://wmo.int/topics/greenhouse-gases

Greenhouse gases (GHGs) in the atmosphere trap infrared radiation from the Earth, keeping it warm, this is known as the greenhouse effect. GHG emissions from human activities provided the majority contribution towards global warming of 1.1 °C.

There are two greenhouse gas effects - natural and enhanced. The natural greenhouse effect is caused by natural amounts of greenhouse gases and is vital to life on this planet. In the absence of the natural greenhouse effect the surface of the Earth would be approximately 33 °C cooler. The enhanced greenhouse effect refers to the additional radiative forcing resulting from increased concentrations of greenhouse gases (GHGs) caused by human activities.  

The main GHGs with rising atmospheric concentrations are carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), hydrochlorofluorocarbons (HCFCs), hydrofluorocarbons (HFCs). Due to long lifetime of the main GHGs they accumulate in the atmosphere.

Emissions from human activities drive the enhanced greenhouse effect and cause climate change. The world is now warming faster than at any point in recorded history.

This change in the atmosphere's chemical composition leads to changes in weather patterns and natural imbalances, which pose enormous risks for human beings and all life on Earth.