The atmosphere is transparent to solar radiation that reaches the Earth. Part of it is absorbed by the Earth´s surface and warms it and part is reflected. But when solar radiation is reflected on the Earth's surface, it loses energy and is transformed into infrared energy that is absorbed by some molecules in the atmosphere (CO₂ , CH₄, H₂O...) (Figure 1). We call these substances GHG (greenhouse gases) because, by retaining part of the heat that the Earth would emit to the outside, they cause the temperature to rise, acting as a greenhouse. 

Before the industrial era, greenhouse gas concentrations were kept at more or less constant levels by natural processes that generated or consumed them (volcanism, decomposition, respiration, photosynthesis, etc.). The radiation absorbed by the Earth and that emitted were kept in balance, providing a temperature suitable for life on Earth. 

The disproportionate emission of these gases since the industrial revolution has upset the balance. To reverse this process we need to know how these gases are generated and act on those sources.

                                                         

Greenhouse effect, NASA/JPL-Caltech, NASA Science, Licencia de la NASA

                              Figure 1. GEI, A loose necktie, Wikimedia Commons, CC BY-SA 4.0                             Figure 2. Greenhouse effect, Physikinger, Wikimedia Commons, CC0 1.0 

Substances containing C and H (hydrocarbons) can react with oxygen, transforming into CO₂ and H₂O and releasing energy. These are called combustion reactions and they allow us to obtain energy from fossil fuels such as coal or oil. 

The invention of the steam engine during the industrial revolution unleashed these combustion processes. The operation of this machine consisted of burning coal, using that energy to convert liquid water into steam and taking advantage of the steam's energy to produce movement. In the 19th century, turbines and pistons that activated the mechanisms of industrial machines, steamboats, trains... were moved by this steam.

Today, thermal power stations operate on the same principle. The steam generated is used to move turbines connected to generators that produce electricity for many homes, offices, factories, schools, hospitals, etc. around the world.

        C + O₂ → CO₂ + H₂0 

There are many other processes that allow us to take advantage of the energy from the combustion reactions. 

For example, to heat homes, kitchens, hot water, etc., natural gas (CH₄) or other fuels such as propane (C₃H₈ ), butane (C₄H₁₀), biomass or wood are burned in boilers, fireplaces or kitchens:

CH₄ + O₂ → CO₂ + H₂0 

C₃H₈ + O₂ → CO₂ + H₂0 

C₄H₁₀ + O₂ → CO₂ + H₂0

Fuels such as diesel or gasoline are burned in the engines of vehicles and machinery to produce their movement. If we simplify the gasoline formula:

C₈H₁₈ + O₂ → CO₂ + H₂0

The amount of combustion reactions that are occurring in the world at every moment, producing CO₂, is exorbitant: Thousands of thermal power stations producing electricity; cars, planes, trains... transporting people; tractors in agricultural tasks to produce the world's food, trucks transporting that food and millions of other consumer items; heating in homes, businesses, public buildings... etc

The following graph shows the data on atmospheric CO₂ concentrations measured by NASA since 1958 (red line) and those from earlier periods, estimated by indirect methods (yellow line). The scientific data show evidence of increasing concentrations since the industrial revolution.

Evidence that atmospheric CO₂ has increased since the Industrial Revolution. Luthi, D., et al.. 2008; Etheridge, D. M., et al. 2010; Vostok ice core data/J. R. Petit et al.; NASA Science, Licensed by NASA.

Climate change refers to long-term changes in temperatures and weather patterns caused by the absorption of heat from excess greenhouse gases produced by human activity.

The chart below shows the change in global surface temperature compared to the pre-industrial average. Earth was approximately 1.36 degrees Celsius warmer in 2023. The most recent 10 years are the warmest on record. NASA's analysis generally agrees with independent analyses prepared by the National Oceanic and Atmospheric Administration (NOAA) and other research groups. 

GLOBAL LAND-OCEAN TEMPERATURE INDEX , NASA Goddard Institute for Space Studies (GISS),  NASA , Licensed by NASA

The data above showed the variation in the Earth's average temperature. But the temperature change is not the same at every point on the planet. There are places that are much more affected by warming. The following video shows how the average temperature recorded at different points on Earth has changed over the last 100 years until 2015.

Temperature variations, bez.es, youtube, CC-BY

• These temperature variations cause changes in the convection currents in the air, changes in the climate, and increase in extreme phenomena such as droughts, torrential rains, hurricanes...
• The ice surfaces of the poles and mountain glaciers are decreasing. As a result, sea levels are rising.In this video you can see how the arctic ice surface has been changing over the last 45 years:

Artic sea ice area variation, NASA/Goddard Space Flight Center Scientific Visualization Studio, NASA, Licensed by NASA

• The increase in ocean temperature causes dissolved CO₂ to be released into the atmosphere , aggravating the problem. 
• Ecosystems and biodiversity are being seriously affected by these changes .
• Apart from extreme climate phenomena, increased drought and desertification can cause difficulties for food production and water access in some zones. The term "climate refugee" already exists for people who have to leave their homes because they have been seriously affected by the climatic consequences.