What exactly is climate?

For scientists, the term “climate” encompasses weather patterns over a long period. Although this term is somewhat abstract, its impact is very real. What is the difference between weather and climate? And what are the climate factors and drivers?

What is the difference between weather and climate?

Grafic discribing temperature progression in Paris-Montsouris in June 2019

Infoclimat.fr (2019). Temperature progression in June 2019 in Paris Retrieved on 13.11.20 from www.infoclimat.fr/observations-meteo/archives/1er/juin/2019/paris-montsouris/07156.html.

Weather

Atmospheric conditions that we can actively feel and experience come under the term weather (e. g. temperature, precipitation, humidity, wind speed and direction, etc.). These are always applicable to a comparatively short period of time (hours, days or a few weeks) and to particular locations or regions. High-speed and high-amplitude weather changes are normal, such as the day-and-night or seasonal cycles.

Climate

The term “climate” refers to the average weather phenomena in a selected place, a large region or across the entire globe over a period of at least 30 years. This time span is defined as a climate normal. Since it covers a large timescale, climate is a slow, more stable system. Changes occur, but at a slower pace, and the fluctuation range is likewise considerably narrower. The climate is determined by a variety of factors.
 

Climate factors and drivers

The prevailing climate of our planet is determined by the following physical factors:

Atmosphere

The concentration of greenhouse gases in the atmosphere plays an important role in the average global temperature

Sun

Solar radiation is the most important source of heat for the climate. Radiation emitted by the sun is subject to cyclical fluctuations

Ocean

Currents such as the Gulf Stream transport vast amounts of energy and the climate of entire regions.

Atmospheric circulation

This distributes gas, water and energy within the atmosphere and defines the regional climate above all.

Landscape and vegetation

Soil conditions and vegetation determine how much radiation is absorbed by the earth’s surface.

Tectonics

The movement of land masses affects how much radiation falls on ocean areas and how much on land masses. Ocean areas absorb more warmth than land masses.

Eccentricity (Milankovitch Cycles)

Earth’s orbit around the sun changes over about 100,000 years. It starts o rounder and becomes more elliptical.

Precession

In about 21,000 years, Earth’s axis rotates once like a spinning top round the vertical axis.

Earth’s Axial Tilt

The tilt of Earth’s axis varies in the course of 41,000 years between 22.5° and 24°

Earth’s climate is the result of all these influences. A change in one or more factors thus brings about a change in the climate. Individual influencing factors, such as volcanic eruptions, have only a short-term effect over a few years. Whereas fluctuations in Earth’s orbit change the climate very gradually over hundreds of thousands of years.
 

Earth’s climate

The atmosphere and its composition play a crucial role in determining the prevailing climate.

This gas envelope is what makes life on Earth possible in the first place, sheltering us from some damaging external influences such as UV radiation.

It is in its lowest layer, the “troposphere”, where weather takes place.

There, winds ensure heat exchange between cold and warm regions. Alongside its primary constituents oxygen and nitrogen, the atmosphere also contains the greenhouse gases water vapour (H2O), carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O).

These gases are able to absorb and re-release long-wave thermal radiation emitted by Earth’s surface. Part of this radiation is returned to Earth’s surface, causing a higher temperature by reducing the cooling effect of heat emission.

This natural process is known as the greenhouse effect and causes an increase in the global average temperature of around 33 °C. Some two thirds of this is caused by water vapour. The remaining third is caused by CO₂ (22 per cent), ozone (7 per cent), N₂O and CH₄.

Consequently, the prevailing average global temperature on Earth is a pleasant +15 °C and not –18 °C, which is what it would be were it not for the greenhouse effect. Greenhouse gas emissions caused by people strengthen this natural effect.

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