This article is from the Economist Magazine. They are enthusiastic supporters of Global Warming/Climate Change and have been for 20+ years. I was therefore surprised to read an article that summarizes the science behind Climate Change and discusses the strengths and weaknesses of the theories in language that can be understood by the average person. The top climate change scientists in the world including James Hansen have finally admitted that the world temperatures are trending way below the Model Forecasts and that something may be wrong with the Theories. This article is a must read for everyone.
I have highlighted important passages and added comments in italics to explain, increase understanding or question. The original can be read at the Economist website if you do not like my comments.April 14, 2013
Climate Science – Article from the “Economist”
A sensitive matter
The climate may be heating up less in response to greenhouse-gas emissions than was once thought. But that does not mean the problem is going away
Mar 30th 2013 | From the print edition of the Economist.
OVER the past 15 years air temperatures at the Earth’s surface have been flat while greenhouse-gas emissions have continued to soar. The world added roughly 100 billion tonnes of carbon to the atmosphere between 2000 and 2010. That is about a quarter of all the CO2 put there by humanity since 1750. And yet, as James Hansen, the head of NASA’s Goddard Institute for Space Studies, observes, “the five-year mean global temperature has been flat for a decade.” (Math/Statistics note: five year mean + decade = 15 years)Hansen is/was widely regarded as the top Climate Change Scientist in the world.
Temperatures fluctuate over short periods, but this lack of new warming is a surprise. Ed Hawkins, of the University of Reading, in Britain, points out that surface temperatures since 2005 are already at the low end of the range of projections derived from 20 climate models (see chart 1). If they remain flat, they will fall outside the models’ range within a few years. (note the last 2 years are already outside of the lower level of the 95% confidence level and that the models were tuned to match the data before 2000 versus predicting it)The mismatch between rising greenhouse-gas emissions and not-rising temperatures is among the biggest puzzles in climate science just now. It does not mean global warming is a delusion. Flat though they are, temperatures in the first decade of the 21st century remain almost 1°C above their level in the first decade of the 20th. But the puzzle does need explaining.
The mismatch might mean that—for some unexplained reason—there has been a temporary lag between more carbon dioxide and higher temperatures in 2000-10. Or it might be that the 1990s, when temperatures were rising fast, was the anomalous period. (how much of the rise may have been due to Natural variability like the sun and Pacific Decadal Oscillation –El Nino and Atlantic Oscillation – AMO ) Or, as an increasing body of research is suggesting, it may be that the climate is responding to higher concentrations of carbon dioxide in ways that had not been properly understood before. This possibility, if true, could have profound significance both for climate science and for environmental and social policy.
The insensitive planet
The term scientists use to describe the way the climate reacts to changes in carbon-dioxide levels is “climate sensitivity”. This is usually defined as how much hotter the Earth will get for each doubling of CO2 concentrations. So-called equilibrium sensitivity, the commonest measure, refers to the temperature rise after allowing all feedback mechanisms to work (but without accounting for changes in vegetation and ice sheets).
Carbon dioxide itself absorbs infra-red at a consistent rate. For each doubling of CO2 levels you get roughly 1°C of warming.(Actually due to the logarithmic decline in back-radiation this is for the first doubling as subsequent doublings have almost no additional effect) A rise in concentrations from pre-industrial levels of 280 parts per million (ppm) to 560ppm would thus warm the Earth by 1°C. (this incorrectly labeled “Greenhouse Theory” is the First of a Series of Three Theories on which Global Warming/Climate Change Theory is based.) If that were all there was to worry about, there would, as it were, be nothing to worry about. A 1°C rise could be shrugged off. But things are not that simple, for two reasons. One is that rising CO2 levels directly influence phenomena such as the amount of water vapour (also a greenhouse gas) and clouds that amplify or diminish the temperature rise. (Note that this is part of the Second Theory and no one has been able to prove that it will increase or decrease the Temp) This affects equilibrium sensitivity directly, meaning doubling carbon concentrations would produce (could lead to) more than a 1°C rise in temperature. The second is that other things, such as adding soot and other aerosols to the atmosphere, add to or subtract from the effect of CO2. All serious climate scientists agree on these two lines of reasoning. But they disagree on the size of the change that is predicted. (This is the Second Theory called Amplification or Feedback Theory.)The Intergovernmental Panel on Climate Change (IPCC), which embodies the mainstream of climate science, reckons the answer is about 3°C, plus or minus a degree or so. In its most recent assessment (in 2007), it wrote that “the equilibrium climate sensitivity…is likely to be in the range 2°C to 4.5°C with a best estimate of about 3°C and is very unlikely to be less than 1.5°C. Values higher than 4.5°C cannot be excluded.” The IPCC’s next assessment is due in September. A draft version was recently leaked. It gave the same range of likely outcomes and added an upper limit of sensitivity of 6°C to 7°C.
A rise of around 3°C could be extremely damaging. (Third Theory is that warming will have Catastrophic Negative Effects.) – The IPCC’s earlier assessment said such a rise could mean that more areas would be affected by drought;(but much higher world humidity is required for the amplification theory to work??) that up to 30% of species could be at greater risk of extinction; that most corals would face significant biodiversity losses;(thousands of feet of carbonates laid down by coral during geological eras like the Devonian with 4000 ppm CO2 and much warmer temperatures??) and that there would be likely increases of intense tropical cyclones and much higher sea levels. (frequency of high strength hurricane/cyclone and tornados has been declining?? and sea level increase is only 8 inches per century??)See graphs at end of article.
New Model Army
Other recent studies, though, paint a different picture. An unpublished report by the Research Council of Norway, a government-funded body, which was compiled by a team led by Terje Berntsen of the University of Oslo, uses a different method from the IPCC’s. It concludes there is a 90% probability that doubling CO2 emissions will increase temperatures by only 1.2-2.9°C, with the most likely figure being 1.9°C. The top of the study’s range is well below the IPCC’s upper estimates of likely sensitivity.
This study has not been peer-reviewed; it may be unreliable. But its projections are not unique. Work by Julia Hargreaves of the Research Institute for Global Change in Yokohama, which was published in 2012, suggests a 90% chance of the actual change being in the range of 0.5-4.0°C, with a mean of 2.3°C. This is based on the way the climate behaved about 20,000 years ago, at the peak of the last ice age, a period when carbon-dioxide concentrations leapt. Nic Lewis, an independent climate scientist, got an even lower range in a study accepted for publication: 1.0-3.0°C, with a mean of 1.6°C. His calculations reanalyzed work cited by the IPCC and took account of more recent temperature data. In all these calculations, the chances of climate sensitivity above 4.5°C become vanishingly small.
If such estimates were right, they would require revisions to the science of climate change and, possibly, to public policies. If, as conventional wisdom has it, global temperatures could rise by 3°C or more in response to a doubling of emissions, then the correct response would be the one to which most of the world pays lip service: rein in the warming and the greenhouse gases causing it. This is called “mitigation”, in the jargon. Moreover, if there were an outside possibility of something catastrophic, such as a 6°C rise, that could justify drastic interventions. This would be similar to taking out disaster insurance. It may seem an unnecessary expense when you are forking out for the premiums, but when you need it, you really need it. Many economists, including William Nordhaus of Yale University, have made this case.
If, however, temperatures are likely to rise by only 2°C in response to a doubling of carbon emissions (and if the likelihood of a 6°C increase is trivial), the calculation might change. Perhaps the world should seek to adjust to (rather than stop) the greenhouse-gas splurge. There is no point buying earthquake insurance if you do not live in an earthquake zone. In this case more adaptation rather than more mitigation might be the right policy at the margin. But that would be good advice only if these new estimates really were more reliable than the old ones. And different results come from different models. (Note recent comment from James Annan who is one of the top Climate Modelers in the world and a contributor/author in the IPCC Reports – “ the stubborn refusal of the planet to warm as had been predicted (by the IPCC including him) over the last decade, all makes a high climate sensitivity increasingly untenable(unlikely). A value (slightly) under 2 C is looking a lot more plausible than anything over 4.5.”)
One type of model—general-circulation models, or GCMs—use a bottom-up approach. These divide the Earth and its atmosphere into a grid which generates an enormous number of calculations in order to imitate the climate system and the multiple influences upon it. The advantage of such complex models is that they are extremely detailed. Their disadvantage is that they do not respond to new temperature readings. They simulate the way the climate works over the long run, without taking account of what current observations are. Their sensitivity is based upon how accurately they describe the processes and feedbacks in the climate system.
The other type—energy-balance models—are simpler. They are top-down, treating the Earth as a single unit or as two hemispheres, and representing the whole climate with a few equations reflecting things such as changes in greenhouse gases, volcanic aerosols and global temperatures. Such models do not try to describe the complexities of the climate. That is a drawback. But they have an advantage, too: unlike the GCMs, they explicitly use temperature data to estimate the sensitivity of the climate system, so they respond to actual climate observations.
The IPCC’s estimates of climate sensitivity are based partly on GCMs. Because these reflect scientists’ understanding of how the climate works, and that understanding has not changed much, the models have not changed either and do not reflect the recent hiatus in rising temperatures. In contrast, the Norwegian study was based on an energy-balance model. So were earlier influential ones by Reto Knutti of the Institute for Atmospheric and Climate Science in Zurich; by Piers Forster of the University of Leeds and Jonathan Gregory of the University of Reading; by Natalia Andronova and Michael Schlesinger, both of the University of Illinois; and by Magne Aldrin of the Norwegian Computing Centre (who is also a co-author of the new Norwegian study). All these found lower climate sensitivities. The paper by Drs Forster and Gregory found a central estimate of 1.6°C for equilibrium sensitivity, with a 95% likelihood of a 1.0-4.1°C range. That by Dr Aldrin and others found a 90% likelihood of a 1.2-3.5°C range.
It might seem obvious that energy-balance models are better: do they not fit what is actually happening? Yes, but that is not the whole story. Myles Allen of Oxford University points out that energy-balance models are better at representing simple and direct climate feedback mechanisms than indirect and dynamic ones. Most greenhouse gases are straightforward: they warm the climate. The direct impact of volcanoes is also straightforward: they cool it by reflecting sunlight back. But volcanoes also change circulation patterns in the atmosphere, which can then warm the climate indirectly, partially offsetting the direct cooling. Simple energy-balance models cannot capture this indirect feedback. So they may exaggerate volcanic cooling.
This means that if, for some reason, there were factors that temporarily muffled the impact of greenhouse-gas emissions on global temperatures, the simple energy-balance models might not pick them up. They will be too responsive to passing slowdowns. In short, the different sorts of climate model measure somewhat different things.
Clouds of uncertainty
This also means the case for saying the climate is less sensitive to CO2 emissions than previously believed cannot rest on models alone. There must be other explanations—and, as it happens, there are: individual climatic influences and feedback loops that amplify (and sometimes moderate) climate change.
Begin with aerosols, such as those from sulphates. These stop the atmosphere from warming by reflecting sunlight. Some heat it, too. But on balance aerosols offset the warming impact of carbon dioxide and other greenhouse gases. Most climate models reckon that aerosols cool the atmosphere by about 0.3-0.5°C. If that underestimated aerosols’ effects, perhaps it might explain the lack of recent warming.
Yet it does not. In fact, it may actually be an overestimate. Over the past few years, measurements of aerosols have improved enormously. Detailed data from satellites and balloons suggest their cooling effect is lower (and their warming greater, where that occurs). The leaked assessment from the IPCC (which is still subject to review and revision) suggested that aerosols’ estimated radiative “forcing”—their warming or cooling effect—had changed from minus 1.2 watts per square metre of the Earth’s surface in the 2007 assessment to minus 0.7W/m ² now: ie, less cooling.
One of the commonest and most important aerosols is soot (also known as black carbon). This warms the atmosphere because it absorbs sunlight, as black things do. The most detailed study of soot was published in January and also found more net warming than had previously been thought. It reckoned black carbon had a direct warming effect of around 1.1W/m ². Though indirect effects offset some of this, the effect is still greater than an earlier estimate by the United Nations Environment Programme of 0.3-0.6W/m ².
All this makes the recent period of flat temperatures even more puzzling. If aerosols are not cooling the Earth as much as was thought, then global warming ought to be gathering pace. But it is not. Something must be reining it back. One candidate is lower climate sensitivity.
A related possibility is that general-circulation climate models may be overestimating the impact of clouds (which are themselves influenced by aerosols). In all such models, clouds amplify global warming, sometimes by a lot. But as the leaked IPCC assessment says, “the cloud feedback remains the most uncertain radiative feedback in climate models.” It is even possible that some clouds may dampen, not amplify global warming—which may also help explain the hiatus in rising temperatures. If clouds have less of an effect, climate sensitivity would be lower.
( clouds can amplify warming by trapping heat but higher clouds can cause cooling by reflecting sun light and heat or by precipitation which cools the air below.)
So the explanation may lie in the air—but then again it may not. Perhaps it lies in the oceans. But here, too, facts get in the way. Over the past decade the long-term rise in surface seawater temperatures seems to have stalled (see chart 2), which suggests that the oceans are not absorbing as much heat from the atmosphere. (Thermodynamically hard to heat water with air temp)
As with aerosols, this conclusion is based on better data from new measuring devices. But it applies only to the upper 700 metres of the sea. What is going on below that—particularly at depths of 2km or more—is obscure. A study in Geophysical Research Letters by Kevin Trenberth of America’s National Centre for Atmospheric Research and others found that 30% of the ocean warming in the past decade has occurred in the deep ocean (below 700 metres). The study says a substantial amount of global warming is going into the oceans, and the deep oceans are heating up in an unprecedented way. If so, that would also help explain the temperature hiatus.
(outlier study for which there is not much data –if air and surface water temperature have not risen much, then how does CO2 heat the deep ocean??)
Lastly, there is some evidence that the natural (ie, non-man-made) variability of temperatures may be somewhat greater than the IPCC has thought. A recent paper by Ka-Kit Tung and Jiansong Zhou in the Proceedings of the National Academy of Sciences links temperature changes from 1750 to natural changes (such as sea temperatures in the Atlantic Ocean) and suggests that “the anthropogenic global-warming trends might have been overestimated by a factor of two in the second half of the 20th century.” It is possible, therefore, that both the rise in temperatures in the 1990s and the flattening in the 2000s have been caused in part by natural variability.
So what does all this amount to? The scientists are cautious about interpreting their findings. As Dr Knutti puts it, “the bottom line is that there are several lines of evidence, where the observed trends are pushing down, whereas the models are pushing up, so my personal view is that the overall assessment hasn’t changed much.”
But given the hiatus in warming and all the new evidence, a small reduction in estimates of climate sensitivity would seem to be justified: a downwards nudge on various best estimates from 3°C to 2.5°C, perhaps; a lower ceiling (around 4.5°C), certainly. If climate scientists were credit-rating agencies, climate sensitivity would be on negative watch. But it would not yet be downgraded. (Expect large reductions if temperatures continue to be below forecasts)
Equilibrium climate sensitivity is a benchmark in climate science. But it is a very specific measure. It attempts to describe what would happen to the climate once all the feedback mechanisms have worked through; equilibrium in this sense takes centuries—too long for most policymakers. As Gerard Roe of the University of Washington argues, even if climate sensitivity were as high as the IPCC suggests, its effects would be minuscule under any plausible discount rate because it operates over such long periods. So it is one thing to ask how climate sensitivity might be changing; a different question is to ask what the policy consequences might be.
For that, a more useful measure is the transient climate response (TCR), the temperature you reach after doubling CO2 gradually over 70 years. Unlike the equilibrium response, the transient one can be observed directly; there is much less controversy about it. Most estimates put the TCR at about 1.5°C, with a range of 1-2°C. Isaac Held of America’s National Oceanic and Atmospheric Administration recently calculated his “personal best estimate” for the TCR: 1.4°C, reflecting the new estimates for aerosols and natural variability.
That sounds reassuring: the TCR is below estimates for equilibrium climate sensitivity. But the TCR captures only some of the warming that those 70 years of emissions would eventually generate because carbon dioxide stays in the atmosphere for much longer.
(Only in a static world – ie the planet is greening up as CO2 increases since all plants on earth grow optimally at 1000 to 2000 ppm of CO2 and require less incremental water – spend the time to view the video of Matt Ridley http://www.rationaloptimist.com/videos – How Fossil Fuels Are Greening The Earth – very highly recommended. Also note the huge seasonal swings in CO2 in northern hemisphere by end of each growing season – a fast growing cornfield will deplete most of the CO2 in the air around the stalks within hours if there is no wind.)
(IF)As a rule of thumb, global temperatures rise by about 1.5°C for each trillion tonnes of carbon put into the atmosphere. The world has pumped out half a trillion tonnes of carbon since 1750, and temperatures have risen by 0.8°C. (since the Little Ice Age – ie some of the .8 C should be the sun or natural variability.) At current rates, the next half-trillion tonnes will be emitted by 2045; the one after that before 2080. (remember the CO2 back radiation only works on first doubling)
Since CO2 accumulates in the atmosphere, this could increase temperatures compared with pre-industrial levels by around 2°C even with a lower sensitivity and perhaps nearer to 4°C at the top end of the estimates. Despite all the work on sensitivity, no one really knows how the climate would react if temperatures rose by as much as 4°C. Hardly reassuring.
From the print edition: Science and technology
The take away from all this is that Catastrophic Anthropogenic Global Warming (CAGW- or Manmade Global Warming/Climate Change) is based on Three Theories that are each dependent on the previous theory – ie they have to work in series.
First Theory is that the first doubling of CO2 should cause an increase of 1 C because of the Infra-red Back Radiation. This has been incorrectly called the Green house theory but greenhouses work by restricting the movement of air or convection. This theory cannot be empirically proven or dis-proven. It should be correct but it may not cause the full 1 C of warming that it should based on the theory because the water vapour radiation spectrum partially overlaps with the CO2 spectrum.
The Second Theory is the Amplification/Feedback Theory that says that as the earth warms there will be an increase in humidity which will cause more clouds which will cause a further increase in temperature in the Troposphere due to trapping of heat by the clouds. This theory is in real question as clouds can also cause cooling by reflecting sunlight/heat and by condensing into precipitation which cools the air below.
The evidence is mounting that the effects of this second theory have been over estimated. There are over 40 years of weather balloon and aircraft readings and 20 years of satellite readings which do not show a temperature or humidity increase in the troposphere. The effect of other Feedbacks like aerosols and soot are also hard to quantify since they usually are not global in impact. The Climate Models do a poor job of handling Clouds and other Feedbacks. The Climate Models may have been programmed with too high of Sensitivity as the actual global temperatures are at the very low edge of the forecasted temperature ranges and are trending way below forecasts. Climate Sensitivity estimates will drop dramatically if temperatures do not rise soon.
The Third Theory is that warming will be bad and will lead to catastrophic events. Large increases in temperature of 4 to 8 C were forecast if Climate Sensitivity was high. If Sensitivity is low then a total increase of less than 2 C would mean only 1 C rise from current time. The following two graphs show declining high strength Hurricanes/Cyclones and Tornados during the recent warming period so a slow 1 C rise is unlikely to cause a dramatic upturn. Some of the positives of mild warming are less fuel use, less cold deaths (see Europe for last 2 winters), minor sea level rise and easier lives. Mild warming combined with higher CO2 concentrations also increases crop yields.
This will be great news for the world if the Climate Crisis has been over estimated and overstated. The 150 billion dollars that the world has spent to date is gone but the world may not have to spend the trillions that scientists and politicians forecasted. The Climate Sensitivity Questions needs to be resolved as quickly as possible but we may have to wait for actual temperatures to be the judge.