The End of Doom

by Ronald Bailey

  So are the models relied upon by the IPCC really all that good at simulating trends in global average temperature? An August 28, 2013, article in the journal Nature Climate Change suggests that they are not. In that study Canadian climate researchers pointed out that while global average temperatures rose over the past twenty years at a rate of 0.14 ± 0.06°C per decade, thirty-seven of the models relied upon by the IPCC simulated an average rise of 0.30 ± 0.02°C per decade. “The observed rate of warming given above is less than half of this simulated rate, and only a few simulations provide warming trends within the range of observational uncertainty,” the authors conclude. It gets worse. For the period after 1998 until 2013, the researchers note, “The observed trend of 0.05 ± 0.08°C per decade is more than four times smaller than the average simulated trend of 0.21 ± 0.03°C per decade.” The upshot is that, according to this study, the climate models are running four times hotter than the observed temperature trends.

  John Christy, a climatologist at the University of Alabama in Huntsville who has long been skeptical of IPCC projections, compared the outputs of seventy-three climate models for the tropical troposphere used by the IPCC in its latest report with satellite and weather balloon temperature trends since 1979 until 2030. “The tropics is so important because that is where models show the clearest and most distinct signal of greenhouse warming—so that is where the comparison should be made (rather than, say, for temperatures in North Dakota),” explains Christy. “Plus, the key cloud and water vapor feedback processes occur in the tropics.” When it comes to simulating the atmospheric temperature trends of the past thirty-five years, Christy found, all of the IPCC models are running hotter than the actual climate. To deflect accusations that he is cherry-picking data, Christy notes that his “comparisons start in 1979, so these are thirty-five-year time series comparisons”—rather longer than the fifteen-year periods whose importance the IPCC report downplays. The private research group Remote Sensing Systems (RSS) also analyzes the satellite temperature data. Like the University of Alabama climatologists RSS reports that “the troposphere has not (their emphasis) warmed as fast as almost all climate models predict.” Comparing IPCC climate model simulations to actual temperatures, RSS finds that “after 1998, the observations are likely to be below the simulated values, indicating that the simulations as a whole are predicting too much warming.” Even the IPCC report admits, “Most, though not all, of [the climate models] overestimate the observed warming trend in the tropical troposphere during the satellite period 1979–2012.”

  The IPCC Physical Science report also concedes that “[a]lmost all [climate model] historical simulations do not reproduce the observed recent warming hiatus.” In fact, the IPCC’s technical summary reveals that 111 out of 114 climate models run hotter than the actual observed temperature trend between 1998 and 2012. What accounts for this apparent predictive failure?

  The IPCC’s Physical Science report suggests with “medium confidence” that internal decadal variability is the cause of much of the difference between observations and the simulations. It’s fair to say that this pause is something of an embarrassment to many in the climate research community, since the computer models failed to indicate that any such thing could happen. Spurred by the mismatch between computer projections and empirical data, lots of climate scientists have been trying to figure out why the average global temperature has not been increasing significantly.

  For example, a 2010 study in Science attributed part of the temperature slowdown to decreases in stratospheric water vapor. A September 2011 article in Nature Climate Change outlined one of the more popular explanations for the pause. Specifically, the missing heat is supposedly hiding in the deep oceans.

  A 2011 article in Atmospheric Chemistry and Physics suggested that a prolonged solar minimum combined with atmospheric aerosols left over from volcanic eruptions reduced the amount of heat reaching the surface of the planet.

  But as noted previously, the most popular explanation by far for why the atmosphere was not warming even as greenhouse gas concentrations were rising was that the excess heat is hiding in the oceans. Some researchers in March 2014 argued in Nature Climate Change that the Pacific Ocean trade winds have speeded up, thus pushing extra greenhouse heat beneath the waves.

  In August 2014 researchers at the University of Washington in Seattle and Ocean University of China in Qingdao countered in Science that the real reason the atmosphere is not warming is that changes in North Atlantic Ocean circulation are burying the extra warmth. The researchers reported that this process could go on for as long as another twenty years before the ocean begins releasing the stored heat, greatly boosting future rates of warming.

  In late August 2014, a team of Japanese climatologists suggested in Nature Climate Change that natural variations in Pacific trade winds account for nearly half of the changes in temperature seen over the past three decades. The bad news, according the researchers, is that natural variation is now being overwhelmed by climate change caused by increasing greenhouse gas concentrations in the atmosphere. Consequently, they predict that man-made warming will dominate future temperature trends soon and the hiatus will end.

  Also in August, Australian researchers associated with the Pacific trade winds theory report in Geophysical Research Letters the results of thirty-one climate models. They find that “under high rates of greenhouse gas emissions there is little chance of a hiatus decade occurring beyond 2030, even in the event of a large volcanic eruption.” As it happens, a study published in October 2014 in Geophysical Research Letters reports that the effects of volcanic particles on global atmospheric temperatures since 2000 have been underestimated, and they have actually cooled the planet by between 0.05 and 0.12 °C. A January 2015 study by researchers at the Lawrence Livermore National Laboratory in California published in Geophysical Research Letters bolstered the findings that sulfuric acid particles from small volcanic eruptions lingering in the boundary between the troposphere and the stratosphere reflect enough sunlight to contribute significantly to the warming hiatus. While volcanic particles in the atmosphere may be masking a warming trend, researchers from the National Center for Atmospheric Research and Duke University in their January 2015 study in Climate Dynamics concluded, “We do not find that aerosols exerted a significant global negative forcing over the last decade or so.” In other words, man-made particulate air pollution has not been significantly cooling the planet during the hiatus. This finding contradicts earlier speculations that man-made aerosols might be responsible for a quarter of the discrepancy between model temperature projections and actual temperature trends.

  In October 2014, two new papers in Nature Climate Change significantly challenged the popular theory that extra heat from greenhouse warming is being buried in the deep ocean. One study analyzed satellite and direct ocean temperature data from 2005 to 2013 and found the ocean abyss below 2,000 meters has not warmed measurably. Basically, satellite measurements between 2005 and 2013 find that sea level has been increasing at rate of 2.78 millimeters per year. Some 0.9 millimeters results from expansion due to warming, and 2.0 millimeters is due to additions of freshwater—for example, melting glaciers. Since 2.9 millimeters is greater than the measured increase of 2.78 millimeters, the researchers concluded that the deep ocean is likely cooling down and thus contracting. In its release describing the work of its researchers, the Jet Propulsion Laboratory noted, “The cold waters of Earth’s deep ocean have not warmed measurably since 2005,” thus “leaving unsolved the mystery of why global warming appears to have slowed in recent years.”

  In a simultaneously published companion paper, JPL researchers suggest that since the extra heat is not hiding in the deep oceans, it must be instead cached in the upper layers of the southern oceans, where it had gone unnoticed due to spotty measurements over the past thirty-five years. As the JPL release explained, “Using satellite measurements and climate simulations of sea level changes around the world, the new study found the
global ocean absorbed far more heat in those 35 years than previously thought—a whopping 24 to 58 percent more than early estimates.” It’s always interesting when models find discrepancies in observational data.

  The effort to explain or explain away the current warming hiatus is ongoing. In a January 2015 Geophysical Research Letters article a French research group noted, “The observed global mean surface air temperature (GMST) has not risen over the last 15 years, spurring outbreaks of skepticism regarding the nature of global warming and challenging the upper-range transient response of the current-generation global climate models.” In an attempt to explain the hiatus, the researchers adjust their climate model to try to take into account how surface winds in the Pacific Ocean could be driving heat uptake in the ocean. Even so, they find that their model still overestimates warming compared to actual temperature trends.

  Also in January, Duke University climatologists analyzed outputs from thirty-four of the climate models used by the Intergovernmental Panel on Climate Change (IPCC) in its Fifth Assessment Report. They report in the Journal of Geophysical Research that the models more or less tracked each other with regard to year-to-year temperature ups and downs but diverged in their explanations for decade-to-decade variability “such as why global mean surface temperatures warmed quickly during the 1980s and 1990s, but have remained relatively stable since then.” Lead author Patrick Brown cautioned, “If you’re worried about climate change in 2100, don’t over-interpret short-term trends. Don’t assume that the reduced rate of global warming over the last 10 years foreshadows what the climate will be like in 50 or 100 years.” On the other hand, Brown also noted, “The inconsistencies we found among the models are a reality check showing we may not know as much as we thought we did.”

  In a January 2015 Nature article, two European climate researchers report the results of comparing the outputs of eighteen climate models used by the IPCC to simulate average global temperature trends from 1900 to 2010 to see how well they match with observed temperature trends. They find that the models actually do simulate similar lengthy hiatuses during that period; they just don’t happen to coincide with the current observational hiatus. They find that due to natural variation, the observed warming might be at the upper or lower limit of simulated rates, but there is no indication of a systematic bias in model process. “Our conclusion is that climate models are fundamentally doing the right thing,” University of Leeds researcher Piers Forster explained. “They [climate models] do in fact correctly represent these 15-year short-term fluctuations but because they are inherently chaotic they don’t get them at the right time.” The Nature article concludes, “The claim that climate models systematically overestimate the response to radiative forcing from increasing greenhouse gas concentrations therefore seems to be unfounded.” Accordingly, the current pause in global average temperature increases is just the result of natural fluctuations in the climate and the man-made trend toward higher temperatures will resume eventually. What natural fluctuations might be responsible for slowing global temperature increases? In a February 2015 article in Science University of Pennsylvania climatologist Michael Mann and his colleagues used climate model simulations to estimate natural variability in North Atlantic and North Pacific Ocean temperatures. They conclude that temperatures in the northern Pacific just so happen to be in cold phase right now which has “produce[d] a slowdown or “false pause” in warming of the past decade.”

  Interestingly, the IPCC’s Synthesis Report found that “ocean warming dominates the increase in energy stored in the climate system, accounting for more than 90% of the energy accumulated between 1971 and 2010 (high confidence) with only about 1% stored in the atmosphere.” The report also suggested that most of the excess heat was stored in the upper ocean, but added that “it is likely that the ocean warmed from 700 m[eters] to 2000 m[eters] from 1957 to 2009 and from 3000 m[eters] to the bottom for the period 1992 to 2005.” Of course, the JPL studies published the month before contradict this assertion.

  Just how long the temperature pause must last before it would falsify the more catastrophic versions of man-made climate change obviously remains an open question for many researchers. For the time being, most are betting that it will get real hot real fast when the hiatus ends.

  The upshot is that many researchers remain convinced that natural fluctuations in the climate unaccounted for in the computer models are responsible for keeping average global temperature flat for the past sixteen to eighteen years. The IPCC’s Physical Science report asserts that the models cannot be expected to simulate the timing of the sort of natural climate variability that has produced the current sixteen- to eighteen-year pause. Georgia Tech climatologist Judith Curry contrarily observed, “If the IPCC attributes to the pause to natural internal variability, then this begs the question as to what extent the warming between 1975 and 2000 can also be explained by natural internal variability. Not to mention raising questions about the confidence that we should place in the IPCC’s projections of future climate change.”

  Overall, the IPCC suggests that the difference between the models and the actual recent temperature trend “could be caused by some combination of (a) internal climate variability, (b) missing or incorrect radiative forcing, and (c) model response error.” That is to say, the projections are off owing to pesky natural climate fluctuations, possible errors regarding estimates of how much warming a given increase in greenhouse gases will produce, and/or boosting temperature projections too high in response to given increases in greenhouse gases.

  Nevertheless, the IPCC believes that the current temperature slowdown will soon end and states, “It is more likely than not that internal climate variability in the near-term will enhance and not counteract the surface warming expected to arise from the increasing anthropogenic forcing.” In other words, when the warm-up resumes, it will soar. By how much? The IPCC Physical Science report projects, “The global mean surface temperature change for the period 2016–2035 relative to 1986–2005 will likely be in the range of 0.3°C to 0.7°C.” This implies increases of 0.15°C to 0.35°C per decade. That would mean that warming could increase at nearly triple the rate the IPCC reports for the period after 1951, and seven times higher than the rate of increase it reports for the last fifteen years. Researchers from the Pacific Northwest National Laboratory published an article in Nature Climate Change in March 2015 in which they compared past rates of temperature change over forty-year periods with future projections. They predict that global average temperature will be increasing at a rate of 0.25C° per decade by 2020. That rate of change would be “unprecedented for at least the past 1,000 years.” If average global temperature began to rise at this rate, it would vindicate the climate models. If not, then what?

  What sorts of changes in “internal climate variability” might soon increase global average temperatures? Warmer and colder water sloshes back and forth periodically in the tropical Pacific Ocean, producing significant changes in global weather. When this El Niño Southern Oscillation (ENSO) pattern is in its warm phase, it substantially boosts the average global temperature. In 2014, many meteorologists were waiting to see if 2014–2015 would conjure up a big ENSO warm phase that would end the hiatus and finally increase global average temperatures above the big 1998 ENSO spike. As of January 2015, the National Oceanic and Atmospheric Administration noted the existence of mild El Niño–like conditions and suggested that Pacific Ocean sea surface temperatures have a good chance of subsiding to a neutral state in 2015.

  The computer climate models are supposed to give policymakers reliable data regarding future trends in man-made global warming. The failure to predict the sixteen- to eighteen-year temperature hiatus has caused some policymakers to wonder if the findings in the IPCC’s Physical Science report really do inspire the kind of confidence that could justify the entailed multitrillion-dollar bet on massive changes to humanity’s energy supply programs.

  The Science Is Settled—Climate Sensitivity


  Another possible explanation for why the computer climate models may be running too hot is what the IPCC refers to as model response error. That is, they may overestimate the amount of warming that results from a given increase in greenhouse gas concentrations in the atmosphere. This brings up the crucial issue of climate sensitivity, conventionally defined as the amount of warming that doubling carbon dioxide in the atmosphere would eventually produce. Temperature increases lag increases in atmospheric carbon dioxide, so another important process is the transient climate response (TCR), which is the amount of warming expected at the time a carbon dioxide concentration crosses the doubling line.

  In its 2007 report, the IPCC estimated that climate sensitivity was between 2° and 4.5°C, with the best estimate being 3°C. The 2013 IPCC Physical Science report drops the lower bound and finds that climate sensitivity is likely in the range 1.5° to 4.5°C. It also states that it is extremely unlikely climate sensitivity is less than 1°C and very unlikely to be greater than 6°C. In addition, the report notes with “high confidence” that the transient climate response is “likely in the range 1° to 2.5°C and extremely unlikely greater than 3°C, based on observed climate change and climate models.” In IPCC parlance, likely means that the authors believe that there is more than a 66 percent chance that they’ve gotten the right estimate for climate sensitivity, whereas extremely unlikely means that they think there is less than 5 percent chance that they are wrong. Just how sensitive the climate is to increases in greenhouse gases is a controversial and hotly disputed area of climate research.

  Several recent studies have reported that climate sensitivity could be lower than the Physical Science summary suggests. For example, an article in the June 2013 Nature Geoscience concluded that the “most likely value of equilibrium climate sensitivity based on the energy budget of the most recent decade is 2.0 °C, with a 5–95% confidence interval of 1.2–3.9 °C.” A confidence interval is basically the probability that a value will fall between an upper and lower bound of a probability distribution. In other words, these researchers are 90 percent confident that climate sensitivity lies somewhere between 1.2° and 3.9°C. The researchers also reported that the best estimate for transient climate response based on observations of the most recent decade is 1.3°C, ranging between 0.9° to 2.0°C.