Global temperatures: what thermometers show and don’t show yet

Conclusions from a series on Bits of Science, about the global temperature trend:

  1. A large part of atmospheric warming is still masked by (shorter-lived) cooling factors and by climate system inertia – therefore the CO2-coupled ‘Real’ Global Temperature is (much) higher than currently observed temperatures.
  2. Recent global temperature records were no ‘peaks’, but rathercorrections to a climatic temperature trend line that is (much) higher than the statistical trend line.
  3. If atmospheric CO2 is stabilised around the current level (404 ppm) there is an uncertain, but possibly large amount of ‘pipeline warming’. This warming in the pipeline may lead to an additional temperature rise of more than 1 degree Celsius – additional warming that will manifest itself after stabilisation of the CO2 concentration. The final temperature rise of the current CO2 concentration could be up to 2 or 3 times as high as the warming that is currently observed(!)
  4. The current atmospheric CO2 level is a dangerous overshoot – to stay below internationally agreed climate targets (both 1.5 & 2 degrees) the CO2 concentration (that is currently still rising year by year) should not be stabilised, but should in fact be lowered.
  5. If we keep measuring climate change by the observed rise in live temperatures and the Earth & climate system responses this temperature rise causes (including extreme weather events) we keep underestimating the real scientific climate urgency.
The below graph shows 4 different temperature trends, against the observed rise of the atmospheric CO2 concentration: 1) observed temperatures (plus annual & 30-year average), an RGT trend based on ‘consensus climate sensitivity’, an RGT trend filtering ocean thermal inertia, and an RGT trend based on long-term ‘Earth System Sensitivity, deduced from Pliocene & Eocene paleoclimate. It shows that at the current CO2 concentration, atmospheric warming could still double:

'Real' Global Temperature - 4 different climate trend lines in one graph, compared to atmospheric CO2 concentration. Please link to Bitsofscience.org
Graph shows (bottom) rising atmospheric CO2 concentration and (top) observed global temperatures (NASA GISS), plus three different values for ‘Real’ Global Temperature (based respectively on climate sensitivity, ocean thermal inertia and – additional expected warming at the CO2 level of that respective year. All temperatures relative to ‘late pre-industrial’ climate baseline. Graph made by climate data journalist Stephan Okhuijsen (Datagraver.com) for the ‘Real’ Global Temperature series of Bitsofscience.org. For full resolution image go to our special graphs page.

[DISCLAIMER: to create above graph we had to make several assumptions, which are explained throughout this article. One thing that deserves special attention is that we draw climate sensitivity as a direct line between preindustrial CO2 (280ppm) and doubled CO2. It’s a nice linear line, but an oversimplification and not correct. In reality warming increases logarithmically with CO2 – the line starts and ends at the same spot, but ought to be more convex shaped in between. The difference is quite large. We use as formula [Tcs = Tpre-indus + ((CO2 – 280)/280) x 3] to get to +1.39 Celsius in 2016. It should be according to [forcing = 5.35*ln(CO2/CO2_ref)] – therefore at 400ppm you already get 51% of warming, so +1.54 degrees. This means the line for Tclimatesens should be higher than graphed above.]

How do recent heat records compare to the global temperature trend?

2014, 2015 and 2016 subsequently broke all the world’s temperature records. That’s why at Bitsofscience.org we started a 25-part series investigating the climate science behind the warming – with one important question: are these ‘insane temperature records’ really peaks on the trend line (as observations suggest), or are we somehow underestimating the warming potency of CO2 and are these temperature ‘peaks’ mere corrections to a higher ‘real’ global temperature trend…?

Today, after quite a lot of hard work, we present the conclusions. We would like to thank the many climate scientists who kindly and freely helped us with this investigation – and the many more whose invaluable (ongoing) research we could draw from!