It is extremely likely that human influence on climate caused more than half of the increase in global average surface temperature from 1951–2010.
Mainstream media and global warming enthusiasts will latch onto that. With little or no awareness of either its textual or its historical context, they will say, “There! See? The 2007 report said only ‘very likely’! This one says ‘extremely likely’! The science is settled! The debate is over! Give it up, you crazy deniers! It’s time, now, to make drastic cuts in greenhouse gas emissions to prevent climate catastrophe!” (Indeed, alarmist climate scientist Andrew Dessler of Texas A&M has already tweeted: “Summary of upcoming IPCC report: ‘Exactly what we told you in 2007, 2001, 1995, 1990 reports…’”)
They will be seriously wrong.
Seriously wrong because, as I’ll explain, (1) describing the probability as “extremely likely” is, well, extremely likely to exaggerate; (2) “the increase in global average surface temperature from 1951–2010” is only about half what the IPCC led the world to believe in its Fourth Assessment Report (AR4, 2007); (3) the far more important claim in the SPM is that “equilibrium climate sensitivity” (ECS) “is likely in the range 1.5C to 4.5C …. The lower limit of the assessed likely range is thus less than the 2C in the [2007 report], reflecting the evidence from new studies.”
Let’s take those items in sequence—and bear with me through a few complicated technical matters.
(1) Describing the probability that “human influence on climate caused more than half the increase in global average surface temperature from 1951–2010” is extremely likely to be wrong. Why? Because of (2) and (3). AR5’s reduction of estimated increase in global average surface temperature 1951–2010 by nearly half, and its reduction of the lower limit of ECS by one-fourth, reflect huge revisions, first, in how scientists process temperature data from around the world, second, in observations (about 0.0C) versus expectations (about 0.3C to 0.4C) of warming over the past 15 to 20 years, and, third, in how modelers understand climate’s response to increased greenhouse gases. Those huge revisions suggest a science enterprise that is far from settled—indeed, farther from “settled” today than it was six years ago—and therefore far from providing a credible basis for an estimate of “extremely likely” (which in IPCC-talk means 95% or higher).
As climatologist If there are substantial changes in a conclusion in the AR5 relative to a confident conclusion in the AR4, then the confidence level should not increase and should probably drop, since the science clearly is not settled and is in a state of flux. While there has been a reduction in either the magnitude of the change or in a confidence level in some of the supporting findings, these changes do not seem to have influenced the main conclusion on climate change attribution: “It is extremely likely that human influence on climate caused more than half of the increase in global average surface temperature from 1951-2010.” The ‘extremely likely’ represents an increase in confidence from the ‘very likely’ of the AR4. An increase in confidence in the attribution statement, in view of the recent pause and the lower confidence level in some of the supporting findings, is incomprehensible to me. Further, the projections of 21st century changes remain overconfident. These inconsistencies seem to me to reflect a failure in meta-reasoning by the IPCC. [Boldface emphasis added.]
(2) “[T]he increase in global average surface temperature from 1951–2010” is only about half what the IPCC led the world to believe in AR4. In AR4, IPCC claimed the rate of warming since 1951 had been about 0.2C per decade; AR5 now says, “The rate of warming since 1951 [has been] 0.12C per decade.” Extrapolate those two different rates to the end of this century and the AR4 claim yields 3C from 1951–2100, while AR5 yields 1.8C. (And anyone who thinks we can prognosticate beyond that—or even, for that matter, to that—only reveals his ignorance of the unpredictability of chaotic non-linear fluid-dynamic systems, of which earth’s climate is an example.)
That might not sound like much, but lots of studies, reflected in IPCC Working Group II’s AR4 and AR5 reports (which focus on impacts rather than causes of climate change), indicate it makes the difference between warming with more harmful than beneficial consequences, and warming with more beneficial than harmful consequences. In other words, that one little change may make the difference between sounding an alarm and celebrating good news. As Matt Ridley pointed out in the Wall Street Journal:
Most experts believe that warming of less than 2 degrees Celsius from preindustrial levels will result in no net economic and ecological damage. Therefore, the new report is effectively saying (based on the middle of the range of the IPCC’s emissions scenarios) that there is a better than 50-50 chance that by 2083, the benefits of climate change will still outweigh the harm.
Warming of up to 1.2 degrees Celsius over the next 70 years (0.8 degrees have already occurred), most of which is predicted to happen in cold areas in winter and at night, would extend the range of farming further north, improve crop yields, slightly increase rainfall (especially in arid areas), enhance forest growth and cut winter deaths (which far exceed summer deaths in most places). Increased carbon dioxide levels also have caused and will continue to cause an increase in the growth rates of crops and the greening of the Earth—because plants grow faster and need less water when carbon dioxide concentrations are higher.
(3) The far more important claim in the SPM is that “equilibrium climate sensitivity” (ECS) “is likely in the range 1.5C to 4.5C …. The lower limit of the assessed likely range is thus less than the 2C in the [2007 report], reflecting the evidence from new studies.”
What is ECS? The amount that global average surface temperature will rise due to doubled atmospheric CO2 (from about 280 parts per million in pre-industrial times to about 560 around the end of this century), including the effects of such climate feedbacks as water vapor, clouds, precipitation, ice coverage, and more.
Until AR5, IPCC had, consistently from 1988 onward, estimated ECS at 2C to 4.5C and had allowed for even higher ranges. Changing the lower limit from 2C to 1.5C is far more significant than you might first think—not primarily because it’s one-fourth lower than the previous lower bound (which is striking in itself), but because it evidences a crack in the previously nearly impregnable foundation of IPCC “consensus science.” IPCC had stubbornly stuck to the 2–4.5C ECS estimate over the last quarter century despite numerous scientific studies pointing to much lower ECS. AR5 at last indicates that IPCC is waking up.
The real world of climate scientists has gone considerably farther than the highly politicized IPCC. Ridley writes, “… these latest IPCC estimates of climate sensitivity may still be too high. They don’t adequately reflect the latest rash of published papers estimating ‘equilibrium climate sensitivity’”—papers pointing at ECS at or well below 2C. (To be fair to IPCC, the rules for its long and cumbersome process include a cut-off date for articles to be included in each assessment, and most of these papers appeared after that date for AR5.)
How much lower might ECS be? Czech theoretical physicist Luboš Motl writes, “The actual scientific evidence makes it ‘extremely likely’ (95+ percent) that the ECS is between 0.5 and 1.5 °C i.e. not far from the generally agreed no-feedback figure close to 1.2 °C. These figures are favored by various observation-based and theory-laden calculations.” The Cornwall Alliance’s 2009 paper A Renewed Call to Truth, Prudence, and Protection of the Poor: An Evangelical Examination of the Theology, Science, and Economics of Global Warming, argued for ECS of about 0.5C on the grounds that climate feedbacks are net negative and eliminate about 58 percent of greenhouse gas warming (1.2C – 58% = 0.504C) and several then-recent observational studies of cloud feedbacks had reached similar conclusions.
There are other significant points in the SPM that have global warming skeptics celebrating—acknowledging that the Medieval Warm Period (which the Third Assessment Report tried to erase from history using the later debunked “hockey stick” graph) was as warm as the present, computer models failed to predict the lack of warming in the last 10 to 15 (really 17+) years and IPCC can’t explain why, models can’t explain sea ice trends, warming by about 2080 will be significantly less than AR4 predicted, etc.—but these three appear to me to be the most significant.What they all point to is the declining credibility of demands for cutting back CO2 emissions by switching from abundant, affordable, reliable fossil fuels to scarcer, more expensive, less reliable wind, solar, and biofuels, the effect of which would be higher energy costs and therefore higher costs for everything else—harming the world’s poor most of all.
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