What do we mean by “human-generated” global warming?

Le January 21, 2021

"It's not my fault." The sharp increase in GHGs is due to human activity.

The graph below shows a sharp increase in GHGs: CO2, methane and nitrous oxide:

  • A relatively stable phase before 1850
  • Exponential acceleration since 1850
--- PICTURE CO2 ---
--- PICTURE CH4 ---
--- PICTURE N2O ---

Focus on CO2. The following diagram illustrates the period from 1750 to 2020:

--- PICTURE CO2 ---

CO2 in the atmosphere and annual emissions (1750-2019)

  • Dark blue curve: CO2 emissions directly generated by human activity.

Before 1850, these emissions were virtually non-existent and stable at less than 1 gigaton of CO2. From 1850, emissions began to increase and accelerated, reaching about 15 gigatons of CO2 emission in 1950, and almost 40 gigatons of CO2 today.

  • Light blue curve: atmospheric CO2 concentration.

The curve is not zero prior to 1850, but it was relatively stable. That confirms the presence of CO2 in the atmosphere, creating a natural greenhouse effect during the preindustrial period.

On the other hand, there was a strong correlation between the direct CO2 emission curve and the atmospheric CO2 concentration curve. These curves show that the concentration of GHGs - and therefore the greenhouse effect - began in around 1850.

This coincides with two events.

The beginning of economic growth.

It may be difficult to imagine, but GDP has not always been increasing. If fact, once upon a time, it didn’t even exist! National wealth stagnated for centuries. As did the standard of living. In the nineteenth century, engineer James Watt developed the coal-fired steam engine, setting off the First Industrial Revolution. The train and new industrial machinery significantly reduced production costs. From 1850, some countries, particularly in Europe, experienced phenomenal economic growth. This triggered a sharp rise in the standard of living in European countries, which gradually spread to all "industrialized" countries. This GDP/capita curve is often shown in the form of a hockey stick.

--- PICTURE ---

Population growth

Improved living conditions due to economic growth generated strong population growth. Between 1850 and 2019, the planet’s population grew from 1.2 billion to 7.7 billion.

--- PICTURE ---

As population grew, the steam and electricity revolutions, among others, followed. Each revolution transformed increasing quantities of natural resources into energy and materials.

Given the increase in the world’s population and growth in GDP per capita, it’s easy to understand why global energy consumption has soared.

Focus on the link between energy and GHG emissions.

80% of the world’s energy currently comes from hydrocarbons. In simple terms: oil, gas, and coal.

These hydrocarbons are called “fossil fuels” because they come from the fossilization of living organisms - algae, plankton and continental plants - that lived long, long ago. That means millions of years in geological terms. Organisms transformed into sediment and were stored in rocks or mineral layers. These resources are called non-renewable or limited because they take longer than the history of mankind to form. New reserves of oil or coal similar to those we have used will not be restored in the next few hundred years.

Hydrocarbons are also called “fuels” because they are burned to release energy, but they also release CO2. These fossilized living organisms contain carbon, which combust when in contact with oxygen, and form CO2.

Energy produced by fossil fuels is prevalent in every aspect of daily life around the world. Fossils fuels are refined and processed to produce energy for domestic and industrial heating. They can also be converted into mechanical energy and electricity with converters, motors and power plants.

  • First place goes to oil

Oil is the most widely used energy in the world. It accounts for almost a third of the world’s energy consumption. It is used as fuel for motor vehicles, fuel and raw material for chemical industries and plastic manufacturing.

  • Coal is in second place.

Despite all the bad press, coal is still widely used, accounting for 27% of the world’s energy consumption. Once used to fuel trains and steam engines, coal is now primarily used to generate heat and power. It is also used in many industries, such as metallurgy and plastics.

  • Third place goes to natural gas.

Not far behind coal, natural gas accounts for 22.2% of global energy consumption. It is mainly used in households, by industry, and to produce electricity.

Our economy is still heavily reliant on fossil fuels that release CO2. Despite its emergence about 30 years ago, renewable energy, from sun or wind for example, only represents a minor part of our energy consumption.

“Human-generated” global warming

Fossil fuels emit large quantities of CO2 and other GHGs. All these GHG emissions are generated by human activity, increasing the amount of GHGs in the atmosphere.

Scientists have also analyzed how much human activity has contributed to global warming compared with overall GHG emissions.

--- GRAPH ---


  • Black bar: observed warming between 1951 and 2010 is +0.7 degrees. This warming is the result of the light and dark blue bars.
  • Dark blue bar: the effect of all greenhouse gases which warm the earth.
  • Light blue bar: the effect of other human effects (such as aerosol
    sprays). They tend to reduce the greenhouse effect and cool the climate.
    The graph shows their effect is much less than the effect of GHGs.
  • Yellow bar: the sum of all human effects. The graph shows that the
    result is positive, which explains current global warming observations.
  • Green bar: natural effects that are not generated by human activity.
    Negligible compared to human effects, they have not impacted current
    global warming.

Many other studies taken into account by the IPCC confirm that it is unquestionable. The link between human activity and global warming is now a proven scientific fact.

IPCC experts are clear in their fifth assessment report: “The influence of mankind on the climate is now clearly established and human greenhouse gas (GHG) emissions are higher than ever.”

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