What causes climate change?
Image: Olivier Mesnage
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 refect 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 removed being removed. How much and how quickly this will accelerate warming is uncertain, although it may have been a contributing factor to the record-breaking warming in 2023.