Scientific consensus, supported by extensive climate data analysis and reports from organizations like the Intergovernmental Panel on Climate Change (IPCC), shows a clear warming trend globally compared to the period before industrialization (typically baseline 1850-1900).
This warming is a primary indicator of ongoing climate change.
The mean global temperature increase measured since pre-industrial times is approximately:
This represents the average rise in surface temperature across the planet over the last century and a half.
The table below lists potential environmental conditions in future climates, related to atmospheric carbon dioxide concentrations ($CO_2$) and mean annual temperature (MAT).
The table also lists potential outcomes with respect to whether conditions will favour grasses with C3 or C4 photosynthetic pathways.
Assuming no other changes in environmental conditions, match the options in the two columns.
| Environmental conditions | Outcomes |
| (P) Increased $CO_2$, no change in MAT | (i) C3 performs better than C4 |
| (Q) No change in $CO_2$, increased MAT | (ii) C4 performs better than C3 |
| (iii) C3 and C4 perform equally |