Will mark brainlistjust need a small paragraph for each heading.

1. Greenhouse gases are the gases which contribute in global warm. Examples are water vapor, carbon dioxide, methane, nitrous oxide and etc. The solar rays which come from the sun are reflected by the Earth surface and they escape to the universe. But greenhouses gases act as a barrier and again reflect those rays towards the Earth. This process is continuous process and helps to keep warm enough to the life unless, the Earth will be a cold planet which is unable to sustain the life.

2. Due to the human activities, the greenhouse gases in the atmosphere have changed. The main greenhouse gas which is increased is carbon dioxide. The reasons for the rising of carbon dioxide level are burning fossil fuels and the deforestation. Since, trees are the only way to absorb atmospheric carbon dioxide naturally, deforestation leads to increase of carbon dioxide level.  

3. In early time, before the industrial revolution era, the concentrations of greenhouse gases are very low and they aren't at a harmful level. But with the industrial revolution, the burning of fossil fuels has increased. Due to that reason, the greenhouse gasses have increased in atmosphere during the time period. The major greenhouse gas which increased is carbon dioxide. Before 1950, the carbon dioxide concentration was under 300ppm. But the current level is more than 400 ppm. This is huge rise during a very short period. Cutting trees also a reason for the increasing of carbon dioxide level.

4.Ice core is a long cylinder which is taken from glacial ice. The ice cores have part of atmospheric air which is trapped in the air bubbles. By measuring the concentration of greenhouse gases which contained in the ice core, we can get the data of greenhouse gas levels in the past. As an example, Antarctic ice cores show that the concentration of carbon dioxide level in past is stable and law before the industrial revolution. Likewise, scientists get the ice cores from glacial ice and measure the carbon dioxide level to get the evidence for the increasing of greenhouse gases.

Ansel nino;