evidence: Human-caused greenhouse gas emissions drive global warming. Obtaining accurate information about the extent of the warming is vital, because it helps us understand if extreme weather events are more likely in the near future, and whether the world is making progress in reducing emissions. [...] But humans have been pumping substantial levels of carbon dioxide into the atmosphere since at least the early 1800s. So the baseline period from which warming is measured should ideally be defined from the mid-1700s or earlier. [...] Our findings suggest that in the interval between the end of our newly defined pre-industrial period and the 30-year average mentioned above, the temperatures of the ocean and land surface increased by 0.9°C. This is far more than the 0.4°C warming the IPCC has estimated, using the conventional timeframe for the pre-industrial period.