How Global Temperatures Predictions Compare to What Happened (Skeptics Off Target)

Skeptical Science has another great post up this week that I just have to repost in full (which includes some pretty wicked graphics). It takes a look at how various climate scientists’ predictions ended up comparing to what we’ve actually seen. As you’ll be able to see, several skeptics basically failed, while leading scientists such as Dr. James Hansen (a regular climate activist, as well as the top climatologist at NASA) and those at the IPCC did pretty darn well.  Here’s a repost of Comparing Global Temperature Predictions:

At this point in the Lessons from Past Climate Predictions series, we’re running out of global temperature predictions to evaluate, so now may be a good time to summarize what we’ve seen thus far.  So let’s just get right to the good stuff:

1976-2011 all predictions

Figure 1:  Various best estimate global temperature predictions evaluated in the ‘Lessons from Past Climate Predictions’ series vs. GISTEMP (red).  The warmer colors are generally mainstream climate science predictions, while the cooler colors are generally “skeptic” predictions.

As you can see in Figure 1, the more mainstream climate science predictions (generally the warmer colors) have mostly done well (Kellogg in 1979 being the main exception), and the “skeptics” (generally cooler colors) have generally done rather poorly, universally predicting less warming than has been observed.

Note that for simplicity and clarity, the figures in this post only include the best estimate predictions/projections of each paper we examined, although some included uncertainty ranges, and others didn’t.  For details regarding each prediction, see the individual posts in the ‘Lessons’ series.

Figure 1 is a bit cluttered, but we can parse the predictions out by isolating the “skeptic” and mainstream predictions.

“Skeptic” Predictions

skeptic predictions

Figure 2: As in Figure 1, but just the “skeptic” predictions.

There are a few interesting things to note from these figures.  For example, we were unable to identify any “skeptic” or global cooling predictions prior to 2000 (note that the few so-called “1970s global cooling predictions” were based on aerosol emissions scenarios which did not occur, and thus are not worth evaluating).  The lone exception in Figure 2 is Lindzen’s, which we reconstructed from comments he made in a 1989 MIT Tech Talk, but which is not a prediction he made himself.

Those few “skeptics” who have made predictions have not fared well thus far.  McLean’s predictionthat 2011 would return to 1956-level temperatures sticks out in particular – we will do a post updating the status of his prediction in the near future.  Akasofu, who predicted 0.5°C global surface temperature warming between 2000 and 2100, has thus far been the closest amongst the “skeptics”.  However, his prediction completely ignores the warming due to the increased greenhouse effect, and in general fails to examine the causes of the temperature changes that he models and predicts.

Mainstream Predictions

mainstream predictions

Figure 3:  As in Figure 1, but just the mainstream climate science predictions.

The global warming predictions made by mainstream climate scientists have all fared reasonably well, with the exception of Kellogg’s in 1979, whose linear nature we found puzzling.  Hansen’s 1988 prediction (we show his Scenario B with the observed greenhouse gas changes taken into account, as described in the Hansen Lessons post) has been somewhat high, mainly because the equilibrium climate sensitivity in the model he used was 4.2°C for doubled CO2, which is higher than today’s best estimate of 3°C.  Overall, the IPCC projections have thus far been the most accurate.

It’s also interesting to specifically examine the projections which applied their models to most or all of the instrumental temperature record (Figure 4).

models to 1890

Figure 4: Broecker and IPCC TAR long-term model runs vs. GISTEMP (red).

The difference between the two models in Figure 4 is that Broecker attempted to incorporate ‘natural cycles’ (which he called ‘Camp Century cycles’, based on Greenland ice core records), whereas the IPCC TAR model only includes anthropogenic effects.  The IPCC TAR model-data comparison clearly shows that human effects had relatively little influence over the early-20th Century warming, but dominated the temperature change since the mid-20th Century.

What’s in Store?

Since the IPCC projections have thus far been the most accurate, it’s worthwhile to see what we have in store if their accuracy continues.  Currently we’re on track with the SRES A2 emissions path, so we can consider this the ‘business-as-usual’ scenario.

Skeptical Science contributor jg has done a great job putting each of the predictions and the combinations above into an animated GIF, finishing off with the AR4 future projections for Scenarios A2 and B1 (Figure 5).  Scenario B1 involves taking serious action to reduce greenhouse gas emissions.

jg gif

Figure 5 final frame: IPCC AR4 Scenario A2 multi-model average global temperature projection to 2100 (blue) and Scenario B1 (green) compared to the ‘danger limit’ of 2°C warming above pre-industrial levels (red).

If we continue on a business-as-usual path, the IPCC AR4 projects that we are most likely on track for 4°C warming above pre-industrial levels by 2100.  We will surpass the ‘danger limit’ of 2°C warming above pre-industrial levels by the mid-21st Century.  Even in Scenario B1 we pass the danger limit, but by a much smaller margin.  This is pretty strong evidence that we need to take action very soon to steer away from our current business-as-usual emissions path.

7 thoughts on “How Global Temperatures Predictions Compare to What Happened (Skeptics Off Target)”

  1. Well, Professor Muller has revealed his finding from his study of temperture records the “skeptics” has claimed were not accurate and fudged. His panel over 18 months had the same findings as the main Climate Science teams. I suppose now the “skeptics” would now at least retreat a bit. Sorry to say they are firm in their denial and are ready for the “next” stage of the “debate”.

  2. Suggested readings:

    “Worse Than We Thought: Evidence Builds That Scientists Underplay Climate Impacts,” Alternet, Oct 18, 2011

    “Climate scientists grapple with uncertainty (though not the kind you think),” Era Klein’s Wonkblog, Washington Post, Oct 18, 2011

  3. Dear Mr Shahan,
    Thank you for another up to date article that is valid and importnt.
    I also view other articles on this subject. The comments that follow are usually dominated by the denier field and they are very vocal in their stance. As far as Global Warming is concerned, now they admit the world is warming and the climate is always “changing” and it is caused by natural forces and is not influenced by man-made emissions. Obviously, their aim is to continue “business as usual”. The sad aspect of it all once you provide “proof”, they steer in another direction and attack the “economics” or the “greedy” scientist that do not provide real world data. I am in an encounter with a few of these chaps with a 140 comment exchange. The “Tea Party” folks, yell, scream and demand and most of all…have the last word. As you stated in your article, time is close at hand and if we do not drop emissions soon, it will not matter. Unfortunately, the politicians are only concerned with th next election.

    1. Thanks! I totally agree. It is a crazy world we live in, and is really a shame what the fossil fuel industry, its paid “grassroots” citizens, and all the people confused by them are doing. Appreciate you chiming in 😀 (and helping to try to educate the ones who can be educated. 😀

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