Note: This post is superseded by the following post !
The transient climate sensitivity (TCR) is the observed average warming of the earth following a doubling of atmospheric CO2 concentration. Effectively this means the observed average temperature when CO2 levels reach 560 PPM. The current average level of CO2 is 415 PPM and we measure the effective temperature of the earth each month relative to a normalised 30 year average. These average temperature anomalies vary from month to month and year to year due to internal effects like El Nino or Volcanoes. This September was the highest recorded temperature anomaly, but this does not mean that temperatures are suddenly accelerating. Instead the trend regularly varies up or down due to internal cycles like El Nino and volcanic eruptions
The best way to measure the underlying sensitivity of the climate to CO2 therefore is to study long term decadal trends. I do this by using a fixed 3D Icosahedral grid, which has the advantage of both having no geometrical biases, and consistency. The method is described here (3) The decadal average simply integrates all recorded temperature anomalies (1961-1990 baseline) over successive 10 year periods. Hence we get the average global temperature anomaly for the 1960s, 1970s etc. These results are remarkably smooth and integrate over ENSO and other short term affects. Therefore I claim this method isolates the underlying enhanced CO2 greenhouse effect from the noise. Here are the results.
Decadal Global temperatures (Red) compared with Moana Loa CO2 levels (Blue, Left Axis)
Assuming a continued linear response gives a result of a 2.5C rise in temperatures in 2100 under business as usual. However this is likely an upper limit because if we also consider the full CO2 range by including the NOAA estimates from before the industrial revolution then we see a lower temperature response to increasing CO2 levels. Note that here the CO2 axis scale has been changed slightly.
Adding the early industrial revolution CO2 levels (NOAA) shows a less than linear temperature response to CO2 levels
I conclude that TCR (Climate Sensitivity) is less than or equal to 2.5C. This means that there is no immediate “Climate Emergency” and we have enough time to solve our future energy needs sensibly.
why the linear relationship only since 1970/80 ? and the disconnect from 1945-65.
seem a bit odd to me if there is a direct relationship of CO2 and temprature.
I suspect we don’t really know the temperature very well before about 1950.
Indeed the global temperature is rising slowly with no “Climate Emergency”. So we have time and should choose the sensible solutions to reduce CO2 emissions like nuclear power.
I received this in an email from Judith Curry.
Causality and climate
Posted on September 26, 2023 by curryja | 736 Comments
Guest post by Antonis Christofides, Demetris Koutsoyiannis, Christian Onof and Zbigniew W. Kundzewicz
https://judithcurry.com/2023/09/26/causality-and-climate/#more-30527
I don’t know if you have read it, or the original papers. I don’t think I have the time, or the necessary skills to unpick it, but I’d love to know others opinions.
Most of the warming since 1980 comes from reduction in cloud cover (CERES and other satellite data). And I think the fate of cloud cover is largely unknown for the future.
Perhaps 1/3 of the warming comes from change in climate gases. So how can it be possible to untangle the contribution from CO2? Lots of uncertainties?
Shorwave cloud feedback is the wild card of climate science.
There has been some estimates on cloud radiation effect from satellite data of “the brightening period”. For the earliest decennia (1980 – 2000) we have 3 scientist groups (Martin Wild, 2009). This is Nikolaos Hatzianastassiou et al, Laura Hinkelmann et al and Rachel Pinker et al. Hatzianastassiou et al 2005 «reveals a significant decadal increase in SW radiation reaching the Earth’s surface, equal to 2.4 Wm?2 , associated with a corresponding decadal increase in surface solar absorption of 2.2 Wm?2, over the 17-year period 1984–2000.» In a publication, 2009, he operates with an increase of 3,5 Wm-2. Laura Hinckelmann et al have a SW radiation down increase of 3,2 W/m2/dec, over the 9 year period 1991 – 99. Rachel Pinker et al have an increase of SW down at the surface of 1,6 W/m2/dec, for the period 1983 – 2001.
The Pinker data has good metodological quality, and seems to be widely accepted, so I`m going to use it as a measure of surface radiation for the first part of «the brightening period». For the rest of the period I think it is safe to uses Loeb`s CERES data. Absorbed solar radiation, ASR, of 0,68 W/m2/dec. (03/2000-02/2021).
So, how can we sum this up? If we use the Pinker data for the years 1983 – 1999, 17 years, and 0,16 W/m2 per year, we get an increase of 2,72 W/m2. And the Loeb data have an increase of 0,068 W/m2 per year for the years 2000 – 2020, 21 years, which gives an increse of 1,43 W/m2. The total increasing shortwave absorption is then 4,15 W/m2 for the years 1983 to 2020. And we can assume that all this increasing radiation comes from changing clouds, and can be called a kind of cloud feedback.
If the negative longwave cloud feedback of Loeb is stable, clouds will have a longwave cooling of 0,15 W/m2/decade. At the same time there will be a shortwave warming from clouds of 4,15 W/m2 from 1983 to 2020, So for 38 years there has been a global cloud radiative warming of 3,58 W/m2.
Clive,
If you look at Fig 7.18 of the AR6
https://www.ipcc.ch/report/ar6/wg1/figures/chapter-7/figure-7-18
your estimate is rather higher than theirs.
The point is that we may well have two doublings before we work out how to help ourselves. 5C is nearly as much warmer as the last glaciation was colder. It isn’t insignificant.
I am going to do this properly soon. The extrapolation above assumes a linear response to CO2 whereas in reality it is less than that. The icosahedral grid has the advantage of being a fixed grid so therefore we can make systematic decadal averages on that grid. Our triangulation mesh varies annually. It works best for monthly and annual averages.