Why? I think there's some intuitive idea that something is being hidden or there's cheating in the presentation, but that doesn't have to be the case if the purpose of the plot is to illustrate relative change (and the y axis is clearly labeled).
The counter-argument is that it makes it look like CO2 has 10x'd instead of doubling, but since those values aren't calibrated in units that we can intuitively understand, it's not obviously the correct choice to start at 0.
Why? I think there's some intuitive idea that something is being hidden or there's cheating in the presentation, but that doesn't have to be the case if the purpose of the plot is to illustrate relative change (and the y axis is clearly labeled).
The counter-argument is that it makes it look like CO2 has 10x'd instead of doubling, but since those values aren't calibrated in units that we can intuitively understand, it's not obviously the correct choice to start at 0.