Menu

What causes climate change?

Image: Olivier Mesnage

  Causes

Other sections

Home > Climate wiki > What causes climate change?

What causes climate change?

Summary

  • See Video 1 for an plain English summary and Video 2 for a comprehensive (also plain English) explanation.
  • The causes of climate change are often called ‘climate forcings’. This term comes from ‘radiative forcing’ or RF, which is the difference between the amount of solar energy (heat) reaching Earth’s atmosphere and the amount that escapes.
  • If more solar energy escapes than arrives (negative RFs) the planet cools. Conversely, if less energy escapes than gets in (positive RFs) the planet warms (Fig. 1). This is because of the Law of Conservation of Energy, a basic law of thermodynamics, which states that:

Energy can neither be created nor destroyed; rather, it can only be transformed or transferred from one form to another.

  • There are many climate forcings, each type determining how much solar energy arrives from the sun, and how much escapes.
  • Natural Forcings happen through natural changes; these were slowly cooling the planet over the past few thousand years (Fig. 1)
  • Anthropogenic Forcings due to human activities are far more powerful. They are causing temperatures to increase much more than natural cooling, and the pace is accelerating (Figs. 1 & 2).

The main climate forcings

  Causes

Other sections

Home > Climate wiki > What causes climate change?

Summary

  • See Video 1 for an plain English summary and Video 2 for a comprehensive (also plain English) explanation.
  • The causes of climate change are often called ‘climate forcings’. This term comes from ‘radiative forcing’ or RF, which is the difference between the amount of solar energy (heat) reaching Earth’s atmosphere and the amount that escapes.
  • If more solar energy escapes than arrives (negative RFs) the planet cools. Conversely, if less energy escapes than gets in (positive RFs) the planet warms (Fig. 1). This is because of the Law of Conservation of Energy, a basic law of thermodynamics, which states that:

Energy can neither be created nor destroyed; rather, it can only be transformed or transferred from one form to another.

  • There are many climate forcings, each type determining how much solar energy arrives from the sun, and how much escapes.
  • Natural Forcings happen through natural changes; these were slowly cooling the planet over the past few thousand years (Fig. 1)
  • Anthropogenic Forcings due to human activities are far more powerful. They are causing temperatures to increase much more than natural cooling, and the pace is accelerating (Figs. 1 & 2).

The main climate forcings

How do forcings work?

If the strength of cooling = warming, the forcings balance one another so the climate stays the same. But when several cooling forcings happen at the same time, they can push Earth into an ‘ice house’ cold state. Conversely, if several warming forcings compound one another, Earth is forced into a hot ‘greenhouse’ state.

One way to think of it is what happens when two people from opposite directions push a stool. You might both be pushing really hard, but if you’re both applying the same exact force, the stool won’t move. Humans are pushing so hard that we can see the climate tipping, overwhelming natural cooling forces (Fig. 1). But we can’t be certain when the climate will crash and break, so we just keep pushing. Once certain tipping points are reached, the geological record shows that the climate will become unstable for several thousands of years until a new stable state is reached.

Aerosols

Some 66% of aerosols are from toxic pollution created by burning fossil fuels. These aerosols reflect solar radiation back into space, which has a cooling effect. However, they also kill 6-7 million people annually (including some 3,300 in Aoteaora). 

International laws to reduce these toxic aerosols from shipping came into effect in 2022, and are gradually being rolled out. By reducing this toxic aerosol pollution the cooling effect of these aerosols is also being removed (Fig. 1)
 Video 1: Earth’s temperature has changed wildly, so what’s the big    deal about a few degrees?
 Video 2: What causes climate change? A fascinating journey into the   past, present, and future.
Fig. 1: The climate forcings that have contributed to climate change from 1850 to 2023.The black line shows the observed global surface temperatures since 1850. 'Natural' forcings (green line) include volcanic eruptions (such as Mt. Pinatubo in 1991) which generally cooled the atmosphere for short periods. It's clear that the cooling effect of volcanic eruptions and even greater cooling effect of aerosol emissions during this period offset some of the warming. When added together, however, all of the cooling forcings aren't enough to offset the main warming forcing: greenhouse gases (grey line) (Image: Zeke Hausfather, January 2025).
Fig. 1: The climate forcings that have contributed to climate change from 1850 to 2023.The black line shows the observed global surface temperatures since 1850. ‘Natural’ forcings (green line) include volcanic eruptions (such as Mt. Pinatubo in 1991) which generally cooled the atmosphere for short periods. It’s clear that the cooling effect of volcanic eruptions and even greater cooling effect of aerosol emissions during this period offset some of the warming. When added together, however, all of the cooling forcings aren’t enough to offset the main warming forcing: greenhouse gases (grey line) (Image: Zeke Hausfather, January 2025).
Fig. 2: The three dominant greenhouse gases in Earth's atmosphere — carbon dioxide (left), methane (center), and nitrous oxide (right) — all reached new highs in 2023. (Image credit: NOAA Climate.gov image, adapted from Figure 2.59 in State of the Climate in 2023. Background photo from Adobe Stock.)
Fig. 2: The three dominant greenhouse gases in Earth’s atmosphere — carbon dioxide (left), methane (center), and nitrous oxide (right) — all reached new highs in 2023. (Image credit: NOAA Climate.gov image, adapted from Figure 2.59 in State of the Climate in 2023. Background photo from Adobe Stock.)
Video 1: World Meteorological Organization – WMO State of the Global Climate 2024

More information