David Stephenson's Global Mean Warming status page
How close are we to 1.5 degrees global mean warming?
The figure below shows monthly global mean temperatures (grey line) relative to the 1850-1900 pre-industrial mean together with a carefully constructed robust trend estimate (in red). The title gives the most recent estimate of
global mean warming (the rightmost point on the trend curve) and the
most recent mean warming rate (the rightmost slope of the trend
curve). The dashed blue lines show the 95% confidence intervals on the
trend estimate:
How I made this plot ...
- I downloaded the most recent HadCRUT monthly mean global mean
temperature data set from http://www.metoffice.gov.uk/hadobs/hadcrut5 at the
Met Office
- I read the data into a data frame object in the R programming language
- I calculated the time mean over 1850-1900 and subtracted it from
all the monthly values to make anomaly values
- I plotted the anomaly values (the grey line)
- I estimated a long-term trend (the red line) and the 95%
confidence interval (the blue lines) by modelling the
anomaly values as the sum of a smooth function of year (the trend), a smooth
function of calendar month, and an irregular AR(2) noise term having
month-to-month persistence. This generalised additive model was proposed by myself and Simon Wood
and demonstrated in Box 2.2 (pages
179-180) of Chapter
2 of the IPCC 5th assessment report (2017).
Download this file trend.csv if you wish to have the trend estimate
and confidence interval lower and upper values shown in the plot.
The HadCRUT5 data were obtained from
http://www.metoffice.gov.uk/hadobs/hadcrut5 and
are © British Crown Copyright, Met Office,
provided under an Open Government License.
A description of how the dataset was made can be found here:
Morice, C.P., J.J. Kennedy, N.A. Rayner, J.P. Winn, E. Hogan,
R.E. Killick, R.J.H. Dunn, T.J. Osborn, P.D. Jones and I.R. Simpson
An
updated assessment of near-surface temperature change from 1850:
the HadCRUT5 dataset. Journal of Geophysical Research
(Atmospheres) doi:10.1029/2019JD032361
Note that estimates of global mean warming differ slightly depending
on various choices such as:
- which global temperature data set to use (there are several)
- which period to use for the preindustrial mean e.g. 1850-1900
- which statistical model to use for the trend process
- what parameter values to use in the trend model
© D.B. Stephenson (2023). All rights reserved.
If you'd like to know more about any of this then please contact me by email on my
profile page.