Interpreting Graphs to Understand Climate Change
This blog post provides a useful trick for interpreting graphs related to climate change. It explains how the temperature and CO2 levels are plotted together, and how to calculate the transient climate response. It is a great resource for understanding the effects of climate change.
Gavin Schmidt
Climate scientist, occasional juggler, even more occasional author, curious about how the world works.
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Here’s a useful little trick for interpreting graphs like the one below.
— Gavin Schmidt (@ClimateOfGavin) March 29, 2023
The temperature & CO2 levels are plotted together with an implicit indication that temperature should be rising as quickly as CO2. But that’s just a function of how the T/ppm y-axes have been scaled. pic.twitter.com/VHKV00CdIl -
That ratio (T/ppm) implies a transient climate response that the grapher wants you to expect. A quick shorthand is to take the temperature range (here 2°C) divide by the CO2 range (60 ppm) and multiply by 290 to get the implied TCR in °C. In this case the answer is 9.7°C
— Gavin Schmidt (@ClimateOfGavin) March 29, 2023 -
Now compare that to the TCR values constrained by observations [1.4, 2.2]°C. Big difference! The axis ratio has been scaled incorrectly by about a factor of 5!
— Gavin Schmidt (@ClimateOfGavin) March 29, 2023
Or perhaps the authors of the graph really think that TCR is almost 10°C (and ECS presumably higher still!). -
Anyway, apply the formula next time you see such a graph, and see what they are implicitly assuming:
— Gavin Schmidt (@ClimateOfGavin) March 29, 2023
Implicit TCR = Delta(T)/Delta(ppm) * 290 -
Notes: the 290 factor comes from a linear fit to the logarithmic forcing function for CO2, for values near 400ppm and an assumption that the radiative forcing for 2xCO2 is about 4 W/m2.
— Gavin Schmidt (@ClimateOfGavin) March 29, 2023 -
This is what a sensible scaling would look like. pic.twitter.com/5ur8MbYGh5
— Gavin Schmidt (@ClimateOfGavin) March 29, 2023