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This section provides you with some very basic answers about climate change and how it works.


To learn more, you can check the latest 2023 IPCC synthesis report or its 2021 report focusing on the Physical Science Basis and its FAQ  

What is climate change and why is it different this time? 

The greenhouse effect is a phenomenon that explains why on planet Earth we are not freezing like on Mars. Some gases in the air, like carbon dioxide, create a sort of blanket or a greenhouse around the Earth preventing the heat from the sun to bounce back to space. This heat that stayed on Earth helped create a climate favorable to animals, plants and humans. This is a natural phenomenon. We call those gases greenhouse gases. 


Throughout the life of planet Earth, its climate has been changing very slowly alternating between ice ages and warmer periods. Those changes were triggered by natural forces such as a slight variation of Earth’s orbit (including its path and the tilt of its axis). On top of those climate variations unraveling through thousands of years, “micro” climate change variations can also happen. They only last decades to centuries before the climate reverts back to its long term trends. Those micro climate change events can be caused  by volcanic eruptions or the sun's energy output. However, for the first time in our planet's history the changes we are experiencing in our climate cannot be explained by those natural forces. The current climate change cycle has been artificially created.  It was triggered by the additional greenhouse gases we, humans, have been sending in the atmosphere since 1850. 

About 200 years ago, we started to make use of something very powerful: fossil fuels. By burning fossil fuels we can power machines (cars, machines which make our clothes, tractors helping farmers to produce more food…), we can produce electricity and heat to warm our homes and power our factories. All these discoveries allowed our great great grandparents up to us to live very comfortably. However, there is a huge downside that for years people were not aware of: by digging up and burning gas, coal and oil we are releasing the carbon they contain.


In addition, industrialization and the increase of the World population also went hand to hand with other phenomenoms that compounded the effects of the burning of fossil fuels. The most important of all was the massive destruction of forests and other carbon dioxide natural "vaccum cleaners" (i.e: those natural ecosystem that traps carbon dioxide within).

Adding all this extra carbon dioxide gas and other greenhouse gases to the atmosphere is making the blanket thicker and thus trapping more heat from the sun. Just like when you add a sweater or a coat in weather to keep the heat of your body trapped so you stay warm. If you take one layer off you get colder if you add one layer you get hotter. For every coat layer worth 1000GtCO2 (1000 billion tons of CO2), temperature increases by roughly 0,45C/ 0.9 F. 

Since 1850 we cumulatively emitted more than 2500GteqCO2.


What are the main greenhouse gases - GHG- ? 

Seven main gases are producing this greenhouse effect. There are listed below in decreasing order of magnitude in terms of human-made emissions (World level): 

  • Carbon dioxide (CO2) is the main driver of the greenhouse effect and contributes to over 75% of the human-related greenhouse gases emissions. Once in the atmosphere, CO2 is very stable. It can take up to 1000 years for CO2 to break into another climate neutral gas. CO2 is mainly released by fossil fuel burning, deforestation and industrial processes such as cement production.


  • Methane (CH4) comes from cattles burps and toots, from landfills and from natural gas extraction. It represents 16% of human-related emissions. Although it is on average 25 times more potent than CO2 in trapping heat, it dissapear faster from the atmosphere (in roughly 12 years).


  • Nitrous oxide (N2O) comes from fertilizers used on farms, industrial processes (especially in chemistry), fossil fuel and biomass burning. It represents roughly 6% of our emissions. It is 265 times more potent than CO2 and stays around 120 years in the atmosphere. 


  • 4 fluorinated gases comprise the last set of greenhouse gases: chlorofluorocarbon-12 (CFC-12) and hydrofluorocarbon-23 (HFC-23) are refrigerant gases used in AC or fridges, sulfur-hexafluoride (SF6) is used in electricity transmission and nitrogen trifluoride (NF3) is used in semiconductor manufacturing. They are super heat trappers, up to 12,000 more potent than CO2 for refrigerant gases. However, their concentrations in the atmosphere are still very low. They represent 2% of our annual emissions.


Which human activities are the main drivers of greenhouse gases emissions ?

Worldwide, the main human activities emitting greenhouse gases are :

  • ENERGY - 25 % of worldwide emissions. They are coming from the burning of coal, natural gas, and oil to produce electricity and heat. An additional 6% is linked to energy and heat generation in houses and buildings (this figure also includes emissions from cooking).

  • AGRICULTURE and FORESTRY - 24%. Those emissions are mostly linked to  cultivation of crops, livestocks and deforestation.

  • INDUSTRY - 21%. Those greenhouse gases are emitted when burning fossil fuels to generate energy onsite, as well as chemical, metallurgical, and mineral processes and waste management.

  • TRANSPORTATION - 14%. They are coming from the gasoline and diesel we used in cars, trains, planes and boats. 

This ranking, which is for human emissions worldwide, varies between countries. For instance, in developed countries, transportation will most often be a bigger emitter than agriculture.

Each of the first 3 sections of the book about “solutions” are built around one of those themes/activities and are ranked following the order of magnitude encountered in most developed countries:

  • First, solutions relating to “Energy” such as electricity and heat production and energy savings.

  • Second, solutions to reduce emissions in “Transportation”: increasing public transportation, increasing the use of fret, reducing travels or using low-emission alternatives to cars.

  • Finally, solutions in the field of “Agriculture” and “Food”, such as agriculture technical changes, changes in diet or the reduction of food waste. 

There is no section on “industry” as a child cannot easily relate to this topic, especially in ways he can be empowered to act.

To learn more about solutions you can implement, go to the "Exploring Solutions" section.

Which physical processes are the main drivers of human production of greenhouse gases ?

There are other ways to breakdown human greenhouse gases emissions than looking at human activities (see above).  Another way is too look at the physical phenomena (driven by humans) which are behind the production of human greenhouse gase.


Using this lense is most reveling for the emission of CO2 (responsible of 75% of all human greenhouse gases) . For the production of CO2, the bottom line is simple : the burning of fossil fuels is the main responsible of humans CO2 emissions. Deforestation and change in land use come second far behind. 



Physical processes behind the production of methane by human activities comes for little less than 1/3 from enteric fermentation of livestock, 1/3 from fossil fuel exploitation and the rest from manure treatment, landfills and waste treatment, rice cultivation and biomass burning and biofuels.

Physical processes behind the production of N2O by human activities are mainly linked to agriculture processes (fertilizers use, manure and manure management), then comes the industry (production of nitric and adipic acid), wastewater, and the combustion of fossil fuels.

A complete breakdown of greenhouse gases emissions and trends by gases is available HERE in the latest IPCC reports.

IPCC_AR6_WGI_Figure_5_5 (1)_edited.jpg

Figure 5.5 | Global anthropogenic CO2 emissions. FROM the IPCC FAQ (a) Historical trends of anthropogenic CO2 emissions (fossil fuels and net land-use change, including land management, called LULUCF flux in the main text) for the period 1870 to 2019, with ‘others’ representing flaring, emissions from carbonates during cement manufacture. Data sources: (Boden et al., 2017IEA, 2017Andrew, 2018BP, 2018Le Quéré et al., 2018aFriedlingstein et al., 2020).

Source: Figure 5.5 in IPCC, 2021: Chapter 5. In: Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [Canadell, J.G., P.M.S. Monteiro, M.H. Costa, L. Cotrim da Cunha, P.M. Cox, A.V. Eliseev, S. Henson, M. Ishii, S. Jaccard, C. Koven, A. Lohila, P.K. Patra, S. Piao, J. Rogelj, S. Syampungani, S. Zaehle, and K. Zickfeld, 2021: Global Carbon and other Biogeochemical Cycles and Feedbacks. In Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [Masson-Delmotte, V., P. Zhai, A. Pirani, S.L. Connors, C. Péan, S. Berger, N. Caud, Y. Chen, L. Goldfarb, M.I. Gomis, M. Huang, K. Leitzell, E. Lonnoy, J.B.R. Matthews, T.K. Maycock, T. Waterfield, O. Yelekçi, R. Yu, and B. Zhou (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, pp. 673–816,

© 2023 Helene Costa de Beauregard and Anita Bagdi 

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