Sets rescale values for the CO2 (mean) dataset to [0.0003908,0.0004225]

[leothomas]

CO2 (mean) measurements are very small, on the other order of ~400 parts per million. With values steadily increasing by about 2.5 parts per million each year, the rescalling factor used when displaying the tiles needs to be updated since more recent values are falling outside of the range of the rescaling factor. There are 2 options:

1. Set rescaling factors to yearly max/min: this will make the seasonal variations most obvious, but will mask the increase in CO2 particles in the atmosphere year to year.
2. Set rescaling factors to dataset max/min: this will "wash out" the seasonal variations slightly but will make the year to year increase visible.

The CO2 scientists has indicated a clear preference for yearly min/max values. For the time being, we have no functionality to change the rescaling factors at any level lower than the dataset level, so option 1. will not be possible for time being.

This PR implements options 2, and we be sure to include this feature request in our discovery efforts for the next iteration of the dashboard/API.

[leothomas]

Before updated rescaling factors:

After updated rescaling factors:

[leothomas]

I also want to mention that I personally find this dataset much more interesting/insightful with dataset min/max values, as the yearly cycles are visible but also the year to year increase, which I believe is as important, if not more, than yearly cycles

January 2015:

July 2015:

January 2016:

July 2016:

January 2017:

July 2017:

January 2018:

July 2018:

January 2019:

July 2019:

January 2020:

July 2020:

January 2021:

June 2021:

[olafveerman]

Thanks @leothomas , I think the second option makes sense, while we wait for a sliding legend to be developed.