As we can see from models of temperature changes caused by natural forcing, we should have observed a decrease in the global average temperature lately, but we have not. We have observed an increase. A climate model can be used to simulate the temperature changes that occur from both natural and anthropogenic causes. The simulations in a) were done with only natural forcings: solar variation and volcanic activity. In b) only anthropogenic forcings are included: greenhouse gases and sulfate aerosols. In c) both natural and anthropogenic forcings are included. The best match is obtained when both forcings are combined, as in c.
From collection: Vital Climate Change Graphics Update
Philippe Rekacewicz, Emmanuelle Bournay, UNEP/GRID-Arendal