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What causes climate change?

What causes climate change?

Image: Olivier Mesnage

What causes climate change?

Summary

  • 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. Until humans appeared, all were natural. Now, the most powerful ones are anthropogenic (man-made).
  • Different climate forcings each determine how much solar energy arrives from the sun, and how much escape.
  • Natural Forcings happen through natural changes; these were very slowly cooling the planet (Fig. 1)
  • Anthropogenic Forcings due to human activities  are far more powerful. They are causing temperatures to increase, and the pace is accelerating (Fig. 1).

Image: Olivier Mesnage

What causes climate change?

Summary

  • 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. Until humans appeared, all were natural. Now, the most powerful ones are anthropogenic (man-made).
  • Different climate forcings each determine how much solar energy arrives from the sun, and how much escape.
  • Natural Forcings happen through natural changes; these were very slowly cooling the planet (Fig. 1)
  • Anthropogenic Forcings due to human activities are far more powerful. They are causing temperatures to increase, and the pace is accelerating (Fig. 1).

The main climate forcings

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 climate will crash, and is likely to be very unstable for thousands of years until it reaches a new stable state.

Fig. 1: The climate forcings that have contributed to climate change from 1850 to 2017. The pale grey line is the observed rise in temperature during that period. Compare the grey line with the orange line (volcanoes,) and it’s clear that the cooling effect of volcanic eruptions 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 (orange line) (Image: composite of graphs from Carbon Brief).

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