1. freezing point
The subpolar and polar regions are the ones that are the coldest on the planet. These regions experience winter for either the whole year, or for most of the year.
The reason why the climate is cold at this parts of the planet is that they receive much smaller amount of sunlight, or rather they receive it at lower angles, so the sunlight is much more dispersed and hits up these regions much less.
For most of the year the temperatures are around or way below the freezing point for water. This is why the majority of the ice cover on Earth is located in the subpolar and polar regions.
2. Temperate
The water is not found in all three conditions in all parts of the planet, but only where the climate allows it. This means that it is a limited part of the planet where the water can be found as a gas, liquid, or solid. The areas that manage to provide these conditions are the temperate regions.
The temperate regions experience more intense sunlight in one part of the year, resulting in high temperatures, so the water is found in liquid form, and as a gas as the evaporation is more intense. When there is less sunlight in the opposite part of the year, the temperature are very low, so the water often solidifies, or rather becomes ice, as the temperatures are below its freezing point.
3. sunlight
The climate zones on Earth are roughly distributed by latitude. The reason for that is the amount of sunlight that is received at any particular latitude.
In accordance to the shape of the planet, the rule is very simple, the lower the latitude, the more sunlight it gets, the higher the latitude, the more sunlight it gets.
In essence, this means that the climates in the lower latitudes are the hottest ones. The climates at the mid-latitude are more moderate, with higher oscillations in temperature and change of seasons. The climates at the high latitudes are the ones that are the coldest, as the sunlight is too little and too dispersed to warm them up properly.
4. Koppen (Koppen-Geiger)
The most widely used climate classification system in the world is the Koppen climate classification system, also referred to as Koppen-Geiger because of the later contributions and modifications made by Geiger to the initial Koppen classification system.
This climate classification system divides the climate on Earth into five major  groups. The division has been based on the temperature patterns and the levels of precipitation. The five major groups are A (tropical), B (dry), C (temperate), D (continental), and E (polar).
The tropical climates are located around the Equator. The dry climates are located just north and south of the tropical climates, around the Tropic of Cancer and Tropic of Cancer. The temperate climates are located in the mid-latitudes, often where there is marine influence, while the continental ones are in the mid-latitudes but deeper into the continents. The polar climates are located at the high latitudes and they are coldest ones on Earth.
5. The analyzing of the climate is not a simple thing. In order to get accurate results, and make accurate models, the scientists have to, and do, use numerous things to make up as rich and as useful data as possible. Basically, every direct and indirect measurement available to the scientists is used.
The instruments like the thermometer and barometer are crucial, but in more modern times that technology has improved a lot, and that has led to the satellite observations to become of great importance for the climate data, especially because the whole world is at disposal to them.
When it comes to the climate of the past and the data about it, the scientists use the rock strata, ice samples, the wood rings, all of which are good sources for the climate and its characteristics at certain times.
