1 Deducing the causes of climate change
Did humans cause recent climate change?
This question is too simple. There’s no switch that selects ‘natural’ or ‘human’ climate change, and there are always natural changes.
So instead we should ask: how much of recent climate change did humans cause?
Estimating the relative contributions of different possible causes of climate change is called attribution. Uncertainty is, of course, inevitable in attribution because establishing cause and effect relationships in complex natural systems is difficult.
Read the following statement and guess the missing value:
Scientists are __% confident that at least half the global warming since 1950 is due to human activities.
Scientists are 95% confident that at least half the global warming since 1950 is due to human activities (IPCC, 2013a).
Did you expect this figure to be higher or lower? As you saw in Session 2, there is also a lot of confusion (and misinformation) about the degree of confidence in the causes of climate change.