The following comment at another thread gives me the perfect introduction into examining another denialists memes, the belief that there has been no warming and that IPCC estimates are way off the mark... proving to denialist's once again that global warming is all a hoax, never mind the upward trending turmoil within our global weather patterns.
Dan Pangburn writes: The 'experts' estimate of the current trend would put the average global temperature trend about 0.2C higher than it is. The temperature trend calculated using my equation is spot on.
I have checked the equation as a predictor (but using actual sunspot data) since 1965. It has never been off in predicting the average global temperature anomaly trend by more than 0.06°C. The equation is calibrated using measurements prior to a date and then used to predict average global temperature trends after that date. The predictions are then compared to the actual measurements to see how well the equation predicted.
That I got it right is demonstrated by accurate calculation and prediction including the flat temperature trend since 2001. Results are shown in the graphs that you saw. The equation predicts an average global temperature downtrend for at least two decades.
To begin you've been accused of butchering the laws of physics, by picking the parts of the equations you like and then substituting fudge constants for the parts you doesn’t like.
"... as explained at least twice, you’re using a correlation metric, not an accuracy metric, so the most you can say is that your equation calculates “something which is sort of correlated with temperatures since 1895″ with a “correlation” of 88%."
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But, what has really prompted this post is your false claim about estimates being wrong.
People can't understand models or expert estimates through hostile soundbite!
We need to take the time to appreciate the complexity of the data and considerations that go into these estimates, only then are you in a better position to judge dodgy claims.
As for explaining some of these more technical aspects, to my mind no one does it better than the volunteers over at SkepticalScience.com ~ they present clear explanations along with references and links so that you can continue your investigation independently.
So I'm going to take advantage of their generous sharing policy to repost one of their threads.
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Add Frame and Stone to the List of Papers Validating IPCC Warming Projections
Posted on 11 December 2012 by dana1981
Just a few weeks ago, a paper in
Environmental Research Letters by
Rahmstorf, Foster, and Cazenave (2012) confirmed the accuracy of the global surface warming projections made by climate models used in the 2001 and 2007 Intergovernmental Panel on Climate Change (IPCC) reports (the Third and Fourth Assessment Reports). Now a new paper published in Nature Climate Change,
Frame and Stone (2012) has confirmed the accuracy of the temperature projections made by the climate models in the 1990 IPCC First Assessment Report through 2011 (Figure 1).
Figure 1: Observed changes in global mean surface temperature over the 1990–2010 period from HadCRUT3 and GISTEMP (red) vs. 1990 IPCC business-as-usual best estimate (dark blue), vs. projections using a one-dimensional energy balance model (EBM) with the measured greenhouse gas (GHG) radiative forcing since 1990 (light blue) and with the overall radiative forcing since 1990 (green). Natural variability from the ensemble of 587 21-year-long segments of control simulations (with constant external forcings) from 24 Coupled Model Intercomparison Project phase 3 (CMIP3) climate models is shown in black and gray. From Frame and Stone (2012).
Frame and Stone Methodology
The paper tests the IPCC warming projections using a simple one-dimensional energy balance model (EBM) comparable to the main model used to make the 1990 prediction, using similar input parameters. Frame and Stone then ran the model using just the radiative forcing (heat imbalance) caused by greenhouse gas (GHG) changes from 1990 through 2011, represented by the light blue line in Figure 1. Because the IPCC model projection is based on GHGs-only, this is the most applicable comparison. They also simulated other radiative forcings like changes in solar activity and particulates in the atmosphere, represented by the green line in Figure 1.
Results Similar to Prior Skeptical Science Analysis
We at Skeptical Science previously conducted
a similar analysis to that in Frame and Stone (2012). The 1990 IPCC report ran simulations using models with
climate sensitivities (the total amount of global surface warming in response to a doubling of atmospheric CO2 concentrations, including all feedbacks) of 1.5°C (low), 2.5°C (best), and 4.5°C (high) for doubled CO2 (Figure 2).
Figure 2: IPCC FAR projected global warming in the BAU emissions scenario using climate models with equilibrium climate sensitivities of 1.5°C (low), 2.5°C (best), and 4.5°C (high) for double atmospheric CO2
In reality, GHGs have increased about 20% slower than the IPCC's "business-as-usual" scenario, in part because of the success of the Montreal Protocol in reducing chlorofluorocarbon (CFC) emissions (CFCs are GHGs), and in part because of the collapse of the Soviet Union, among other reasons.
Figure 3: 1990 IPCC business-as-usual "best" global warming projection reflecting the observed GHG changes (blue) vs. observed average global surface temperature change from GISTEMP (red) since 1990.
Observed Warming Not Natural Variability
Frame and Stone (2012) also simulated the possible range of natural temperature variability since 1990 by using the ensemble of 587 21-year-long segments of control simulations with constant external forcings from 24
Coupled Model Intercomparison Project phase 3 (CMIP3) climate models. These give a 90% range of about ±0.19° C, and are shown in black and gray in Figure 1. The observed warming from 1990 through 2011 was approximately
0.39±0.20°C (95% confidence range); thus there is only a very small chance that the observed global surface warming over the past 21 years could be explained purely by natural variability.
IPCC Has Excelled at Global Warming Projections
Ultimately, Frame and Stone note that while there is a fairly large range in the envelope of all climate model projections, and while to some degree they may have gotten the right answer 'for the wrong reasons', the IPCC has thus far done quite well in projecting future temperature changes.
"...it seems highly likely that even in 1990 we understood the climate system well enough to make credible statements about how its aggregate properties would change on timescales out to a couple of decades, even in the presence of considerable uncertainty surrounding the exact forcing trajectory."
Rahmstorf, Foster, and Cazenave (2012) arrived at a similar conclusion by taking a very different approach, first using the statistical technique of multiple regression to filter out much of the short-term variability, then showing that the IPCC temperature projections have been very accurate (Figure 4).
Figure 4: Observed annual global temperature, unadjusted (pink) and adjusted for short-term variations due to solar variability, volcanoes and ENSO (red) as in Foster and Rahmstorf (2011). 12-month running averages are shown as well as linear trend lines, and compared to the scenarios of the IPCC (blue range and lines from the 2001 report, green from the 2007 report). Projections are aligned in the graph so that they start (in 1990 and 2000, respectively) on the linear trend line of the (adjusted) observational data. From Rahmstorf, Foster, and Cazenave (2012).
Frame and Stone have also shown it is very unlikely that natural variability alone can account for the observed global surface warming over the past two decades.
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For further learning
