Climate Code Red: Dangerous climate change: Myths and reality, Part 1 of 3

by David Spratt, Climate Code Red, August 22, 2014

Part 1 in a 3-part series | Part 2 | Part 3

Download report (16 pages)

Few would disagree that the world should avoid "dangerous" (or unsafe) climate warming, but what does that term mean? What does climate safety mean? Is climate change already dangerous? Are greenhouse gas levels already too high? This report surveys some recent developments in climate science knowledge as a way of discerning the gaps between myth and reality in climate policy-making.

Scientific and political reticence

Amongst advocates for substantial action on climate warming, there is a presumption of agreement on the core climate science knowledge that underlies policy-making, even though differences exist in campaign strategy.

But the boundaries between science and politics have become blurred in framing both the problem and the solutions. Amongst advocates, advisors and policy-makers there are very different levels of understandings of the core climate science knowledge, how it is changing, what constitutes "danger," what needs to be done, and at what pace.

• Download full report as PDF

On the science side, the challenge is of a fast-developing discipline in a rapidly changing physical world. There is a concerted and unwarranted global attack on climate scientists and, in Australia, intimidation and fear of job loss generated by the Abbott government’s hostility to science and cuts in climate research funding. As well, there are always uncertainties and unknowns in science, and difficulties in communicating complex understandings in a non-technical manner. Together these factors can produce over-cautiousness in public presentation and scientific reticence.

In his 2011 climate science update for the Australian Government, Prof. Ross Garnaut gave some "reflections on scholarly reticence," questioned whether climate research had a conservative "systematic bias," pointed to "unfortunate delays between discovery and influence in the policy discussion," and asked "whether the reason why most of the new knowledge confirms the established science or changes it for the worse is scholarly reticence." Garnaut pointed to a pattern across diverse intellectual fields of research being "not too far away from the mainstream," but says in the climate field that this "has been associated with understatement of the risks."

With masterly restraint, he concluded that we should be "alert to the possibility that the reputable science in future will suggest that it is in Australians’ and humanity’s interests to take much stronger and much more urgent action on climate change than might seem warranted from today’s peer-reviewed published literature. We have to be ready to adjust expectations and policy in response to changes in the wisdom from the mainstream science" (Garnaut, 2011).

On the politics side, often insufficient attention is paid to the breadth and depth of published research, and there is a tendency to prioritise perceived political relevance over uncomfortable scientific evidence. Most climate advocacy organisations allocate few resources to critically interrogating the climate research as part of strategy and policy development, and generally fall into a middle-of-the-road advocacy consensus which downplays the warnings from the more forthright scientists whose expert elicitations – on such topics as the stability of ice sheets and sea ice to future sea-level rises – have generally proven more robust than those of their more reticent colleagues.

A desire amongst advocacy organisations to stick together and present a common mainstream view is understandable, but Garnaut has pointed out the scientific danger, and his observation is just as powerful for climate politics. There is little point in constructing campaign strategies discordant with a fast-changing reality.

The mainstream representation of climate science as it blurs with politics – in public discourse in Australia, across most civil society sectors, and at the global policy-making level – could reasonably be described as follows:

• Climate change is not yet dangerous, and two degrees of warming (2 °C) is the appropriate focus for policy-making, because 2 °C impacts are manageable and big tipping points are unlikely before 2 °C.
• We should plan to mitigate (reduce emissions) for 2 °C, but we may fail so we should also plan to adapt to 4 °C (which is the likely "business-as-usual" outcome by 2100 if high rates of emission continue).
• We have a substantial carbon budget left for 2 °C, because long-term feedbacks are not materially relevant, and high risks of failure can be accepted because 2 °C is a “target” (which can be exceeded) rather than a “cap” (an upper boundary not to be exceeded).
• Hence, there is time for an orderly, non-disruptive reduction in emissions within the current political and economic paradigm.

Much of the recent international policy discourse has focused on "what percentage reductions by when and by whom" in emissions would stop warming passing 2 °C. In Australia, is it 5% by 2020, or 19%, or a lot more? Till 2030 or 2050? An observer of this discourse would not think that 2 °C is other than a reasonable target and that we have plenty of carbon emissions left for a few decades more. They would certainly not understand that such propositions are dangerous myths. Here's why.

Myth 1: Climate change is not yet dangerous

In 2008, John Holdren, who was then senior advisor to President Barack Obama on science and technology issues, told the Eighth Annual John H. Chafee Memorial Lecture on Science and the Environment: "… the (climate) disruption and its impacts are now growing much more rapidly than almost anybody expected even a few years ago. The result of that, in my view, is that the world is already experiencing dangerous anthropogenic interference in the climate system ” (emphasis added) (Holdren, 2008).

“Dangerous” climate changed is broadly characterised by the Intergovernmental Panel on Climate Change (IPCC), in the “burning embers” diagram, as including five “reasons for concern”: risk to unique and threatened systems, risk of extreme weather events, distribution of impacts, aggregate (total economic and ecological) impacts, and risk of large-scale discontinuities (that is, abrupt transitions or “tipping points”) (see Figure 1).

From this perspective, tipping points have already been passed, at less than 1 °C of warming, for:

• The loss of the Amundsen Sea West Antarctic glaciers, and 1–4 metres of sea level rise (Rignot, Mouginot et al., 2014; Joughin, Smith et al., 2014). Dr Malte Meinshausen (advisor to the German government and one of the architects of the IPCC's Representative Concentration Pathways) calls the evidence published this year of “unstoppable” (Rignot, 2014) deglaciation in West Antarctica “a game changer” and a “tipping point that none of us thought would pass so quickly,” noting now we are “committed already to a change in coastlines that is unprecedented for us humans” (Breakthrough, 2014). 
• The loss of Arctic sea-ice in summer (Duarte, Lenton et al., 2012; Maslowski, Kinney et al., 2012), which will hasten regional warming, the mobilization of frozen carbon stores, and the deglaciation of Greenland.
• Numerous ecosystems, which are already severely degraded or in the process of being lost, including the Arctic (Wolf, 2010). In the Arctic, the rate of climate change is now faster than ecosystems can adapt to naturally, and the fate of many Arctic marine ecosystems is clearly connected to that of the sea ice (Duarte, Lenton et al., 2012). In May 2008, Dr Neil Hamilton, who was then director of Arctic programmes for WWF, told a stunned audience (of which I was a member) at the Academy of Science in Canberra that WWF was not trying to preserve the Arctic ecosystem because “it was no longer possible to do so.”

Many extreme weather events that have been made worse by climate change and variations of the Jet Stream — including Superstorm Sandy, Typhoon Haiyan and extraordinary heat waves in France (2003) and Russia (2010) and associated death tolls of many thousands — are also evidence that climate change is already dangerous.

The current level of greenhouse gases is around 400 ppm carbon dioxide (parts per million CO2), and 470 ppm carbon dioxide equivalent (CO2e) when other greenhouse gases including methane and nitrous oxide are included. The last time CO2 levels were as high as they are today, humans didn't exist, and “CO2 values associated with major climate transitions of the past 20 millions years are similar to modern levels” (Tripati, Roberts et al., 2009). In other words, big changes (“transitions”) in significant climate system elements, such as ice sheets, sea levels and carbon stores, are likely to occur for the current level of CO2. From the study of climate history, we learn that:

• “During mid-Miocene climatic optimum  [16–14 million years ago] CO2 levels were similar to today, but temperatures were ~3–6C warmer and sea levels 25–40 metres higher than at present… When CO2 levels were last similar to modern values (greater than 350–400 ppmv), there was little glacial ice on land, or sea ice in the Arctic, and a marine-based ice mass on Antarctica was not viable… Lower levels were necessary for the growth of large ice mass on West Antarctica (~ 250–300 ppmv) and Greenland (~ 220–260 ppmv)" (Tripati, Roberts et al., 2009).
• “We estimate sea level for the Middle Pliocene epoch [3.0–3.5 million years ago] – a period with near-modern CO2 levels – at 25 ± 5 metres above present, which is validated by independent sea-level data” (Rohling, Grant et al., 2009).
• Likewise, “during the middle-Pliocene … we find sea level fluctuations of 20–40 metres associated with global temperature variations between today’s temperature and +3 °C” (Hansen, Sato et al., 2013).

Figure 1.  The ‘burning embers’ diagram 
from the IPCC’s Fifth Assessment Report illustrates risks for five key areas of concern.  Note that for “Large-scale singular events” (right-hand column) the risk at the current level of warming is assessed as “undetectable,” whereas there is now clear evidence that dangerous tipping points have been already passed for significant elements of 
the climate system.

Myth 2: Two degrees is an appropriate focus for policy making

The evidence above indicates that dangerous tipping points have already been passed at the current level of climate warming of 0.8 °C, so 2 °C of warming is clearly not an appropriate focus for policy making. 2 °C is a very unsafe target in any framing of risk. It is more appropriately considered as the boundary between dangerous and very dangerous climate change (Anderson & Bows, 2010). In Australia, 2 °C would likely mean, amongst many impacts, the loss of the Great Barrier Reef, the salination of Kakadu, and the loss of the north Queensland tropical rainforests.

This is consistent with a framework of “planetary boundaries” published in 2009, which “define the safe operating space for humanity with respect to the Earth system and are associated with the planet’s biophysical subsystems or processes” (Rockstrom, Steffen et al., 2009). It proposes a boundary of less than 350 ppm CO2e, compared to the current level of more than 470 ppm CO2e.

Research also finds that:

• 1 °C of warming over the pre-industrial baseline — which we are now approaching — is hotter than the Holocene maximum (the period of human civilisation up to 1900)  (Marcott, Shakun et al., 2013; Hansen, Kharecha et al., 2013) (see Figure 2).
•  For 2 °C of warming, the sea-level rise will likely eventually be measured in the tens of metres (Rohling, Grant et al., 2009).
• Hansen and Sato (2012), using paleoclimate data rather than models of recent and expected climate change, warn that “goals of limiting human-made warming to 2 °C and CO2 to 450 ppm are prescriptions for disaster” because significant tipping points – where significant elements of the climate system move from one discrete state to another – will be crossed. As detailed in the next section, numerous tipping points are likely well before 2 °C.

As well, the IPCC considers that the risks to unique and threatened systems, and of extreme weather events, is high at 2 °C of warming (see Figure 1).

Note: References available at PDF download

• Download full report as PDF

http://www.climatecodered.org/2014/08/dangerous-climate-change-myths-and.html

Joe Romm: Words Matter When Talking Global Warming: The ‘Good' Anthropocene Debate

by Joe Romm, Climate Progress, June 19, 2014

CREDIT: SHUTTERSTOCK

We spend more of our waking hours communicating than perhaps any other single activity. And while the principles of effective writing and speaking have been understood for centuries if not millennia, they are largely ignored today — sometimes intentionally, as Orwell pointed out nearly seven decades ago.

“In our time, political speech and writing are largely the defense of the indefensible,” George Orwell wrote in “Politics And The English Language” in 1946. “Thus political language has to consist largely of euphemism, question-begging and sheer cloudy vagueness.”

Nowhere is that clearer than in the arena of climate politics and journalism — which often seems driven by the unproductive extremes of “Don’t Worry, Be Happy” and “STAND BACK AND WATCH THE WORLD BURN.” Ultimately, they are both equally pessimistic, since they both push the premise that there is no chance the human race could actually embrace the kind of aggressive action needed to have a realistic chance of avoiding multiple catastrophes.

I am more optimistic, as I explained in my reply to Ezra Klein’s pessimism. I suppose if I had a motto, it might be: Do Worry, Take Action, THEN Be Happy.

I’ve been thinking about all this because I was on two recent science communications panels: a “Science & Policy Communications Workshop” this week for the American Geophysical Union (AGU) and a Communications Workshop at the American Meteorological Society (AMS) Summer Policy Colloquium last week. Everything I know on the subject can be found in my 2012 book, “Language Intelligence: Lessons on Persuasion from Jesus, Shakespeare, Lincoln and Lady Gaga.”

For those who want the pithy version, start with the great 20th Century essayist, Orwell, in his greatest essay, “Politics And The English Language” — and the great 20th Century orator, Winston Churchill, in his essay metaphorically titled, “The Scaffolding of Rhetoric.”

Orwell offers six simple rules for writing with clarity, “rules that one can rely on when instinct fails,” when you are “in doubt about the effect of a word or a phrase”:

• (i) Never use a metaphor, simile, or other figure of speech which you are used to seeing in print.
• (ii) Never use a long word where a short one will do.
• (iii) If it is possible to cut a word out, always cut it out.
• (iv) Never use the passive where you can use the active.
• (v) Never use a foreign phrase, a scientific word, or a jargon word if you can think of an everyday English equivalent.
• (vi) Break any of these rules sooner than say anything outright barbarous.
What’s interesting is that in his essay, Churchill says some very similar things even though he is focused on oratory. “There is no more important element in the technique of rhetoric than the continual employment of the best possible word,” he argues. “Whatever part of speech it is it must in each case absolutely express the full meaning of the speaker. It will leave no room for alternatives.”
So clarity is king, just as it is for Orwell. Churchill then takes on a very common myth about rhetoric:

The unreflecting often imagine that the effects of oratory are produced by the use of long words…. The shorter words of a language are usually the more ancient. Their meaning is more ingrained in the national character and they appeal with greater force to simple understandings than words recently introduced from the Latin and the Greek. All the speeches of great English rhetoricians … display an uniform preference for short, homely words of common usage….

Short words win. Jargon loses.
In preparing for my AMS and AGU talks, I asked a senior legislative aide with over two decades of Hill experience for some advice. He told me that if scientists speak to a Legislative Assistant (L.A.) for a member on the climate issue, they “can’t assume the L.A. knows anything.” It would be a mistake, he said, to even use a phrase like “statistically significant”!
Susan Joy Hassol, an expert in climate communication, made the same point in a 2010 post here — avoid jargon: “Words that seem perfectly common to scientists are still jargon to the wider world and always have simpler substitutes. Rather than anthropogenic, you could say human caused.”
And this bring us to the latest dust-up over jargon and euphemism. The New York Times climate blog published a piece titled, “Exploring Academia’s Role in Charting Paths to a ‘Good’ Anthropocene.”
I think it’s safe to say that both Orwell and Churchill would have gagged at “Anthropocene,” which, as perhaps 1% (0.1%?) of the U.S. population knows, means “an informal geologic chronological term that marks the evidence and extent of human activities that have had a significant global impact on the Earth’s ecosystems.”
Inside the tiny community of people who actually understand the term, there was widespread objection to the entire phrase, “Good Anthropocene.” Australian author, climate expert and Professor of Public Ethics Clive Hamilton wrote, “those who argue for the ‘good Anthropocene’ are unscientific and live in a fantasy world of their own construction.”
I very much agree. Elizabeth Kolbert, one of the most thoughtful climate journalists, tweeted: 



The NY Times blogger (Andy Revkin) criticized Kolbert for having tweeted that without having watched the hour talk he gave, “Paths to a ‘Good’ Anthropocene” (video here).
After she watched it, Kolbert emailed me:

I don’t see the value in the “good Anthropocene” as a rhetorical construct, even if it’s well-intentioned. What we are doing to the planet, which is of course the reason geologists are considering renaming the epoch in which we live, is in no way good. A few years ago, Paul Crutzen told me that he hoped the word Anthropocene would serve as “a warning to the world.” I think part of the power of the term is that it resists modification.

I’ve watched the video. In its own way, it is just as much a pessimistic, self-fulfilling prophecy as Ezra Klein’s “7 reasons America will fail on climate change.” We know what we need to do to avoid catastrophic warming — quickly embrace a series of policies (at a national and global level) including a carbon price that drive emissions down sharply decade after decade. The good news is that the world’s leading governments and scientists and energy experts have explained that this strategy is cheap (far cheaper than inaction), and that we have the technology to start ASAP. Oh, and deployment-driven innovation will keep providing new and better and cheaper technology.
It is certainly a legitimate view to argue that the nation (and the world) aren’t up to that task, as Klein and Revkin do. But it is Orwellian to climate that making such an argument is optimistic and not self-fulfilling. That’s especially true if your recommended alternative is to basically give up (Klein) or to abandon quantitative targets and embrace personal growth and some R&D (Revkin).
As Hamilton writes:

The advocates of the “good Anthropocene” do not attempt to repudiate the mass of scientific evidence; instead they choose to reframe it. As you declare so disarmingly in your talk: “You can look at it and go ‘Oh my God’, or you can look at it and go ‘Wow, what an amazing time to be alive!’ I kind of choose the latter overall.”

Talking of a “good Anthropocene” while proposing strategies that can’t possibly achieve it — and while repeatedly attacking those (including the National Academy of Sciences) who propose strategies that could — is the road to a very, very bad Anthropocene. In jargon-free terms, it is the road to Hell and High Water.
The phrase “good Anthropocene” as some are using it, is a euphemism as Orwellian as “enhanced interrogation.” As Hamilton puts it:

… the “good Anthropocene” is a story about the world that could have been written by the powerful interests that have got us into this mess and who are fighting so effectively to prevent us from getting out of it. In the long term this kind of thinking will prove more insidious than climate science denial.

The eco-pragmatists, as Hamilton calls them, never offer any set of specific proposals that any credible group of independent experts has said could possibly keeps us far from 7 °F warming (the end of modern civilization as we know it) — let alone the unimaginable 10+°F. All they offer is the euphemism, hand-waving, and sheer cloudy vagueness Orwell warned about.
Revkin tweets: “I trust those bridling at vision of a “good” #Anthropocene aren’t hoping for bad one. http://nyti.ms/1qdcd0F @CliveCHamilton @ElizKolbert.”
Seriously. Hamilton and Kolbert have dedicated themselves to informing the public about the worst impacts — and how to avoid them. Kolbert’s terrific 2006 book, Field Notes from a Catastrophe, famously ends, “It may seem impossible to imagine that a technologically advanced society could choose, in essence, to destroy itself, but that is what we are now in the process of doing.”
That kind of clarity is what we are missing from the current discussion. The climate debate isn’t about what people are “hoping for” — it is about the kind of future that we are choosing through our climate policy. So far we have chosen poorly.

http://thinkprogress.org/climate/2014/06/19/3450400/orwell-language-good-anthropocene/

Michael Mann, SciAm: Earth Will Cross the Climate Danger Threshold by 2036

The rate of global land-surface temperature rise may have hit a plateau, but a climate crisis still looms in the near future

by Michael E. Mann, Scientific American, March 18, 2014

Danger Zone in 22 Years: Click on this link to enlarge the image above:  https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEijbJYYmWeIWi3YWMChXRoWnd1C0AoH0RandMKKPuYEOdFPbPrnxKlH-S7uDqKmpg9CX4s0IE9TA_1MwTXJaQ2gJF-LijzQqBLFsVVDxXa8ERZTiEgWoAyLUAMbwhBCBFa3RbkDmsYl69o/s1600/MikeMann.SciAm.FalseHope.March2014.png

If the Northern Hemisphere's surface temperatures rise more than two degrees Celsius above preindustrial levels (baseline), human civilization will suffer dangerous harm, scientists say. When will that occur if the world keeps burning fossil fuels at current rates? The answer comes from entering estimates for equilibrium climate sensitivity (ECS)—how sensitive the atmosphere is to the heating effect of greenhouse gases (five solid curves)—into a so-called energy balance model of climate. The estimate that best agrees with recorded data reflecting the sensitivity of the earth's climate (white) indicates that the world will cross the two degrees C threshold in 2036, only 22 years from now (orange). If the reported recent slowdown in the rate of temperature rise, sometimes inappropriately called “the pause,” proves to be part of a more persistent pattern, then a different estimate (gold) best fits the past 15 years or so, and it gives the world until 2046 to cross the danger line.

Credit: Pitch Interactive; SOURCE: MICHAEL E. MANN

In Brief

• The rate at which the earth's temperature has been rising eased slightly in the past decade, but temperature is still increasing; calling the slowdown a “pause” is false.
• New calculations by the author indicate that if the world continues to burn fossil fuels at the current rate, global warming will rise to two degrees Celsius by 2036, crossing a threshold that will harm human civilization.
• To avoid the threshold, nations will have to keep carbon dioxide levels below 405 parts per million.

More In This Article

• 

  Why Global Warming Will Cross a Dangerous Threshold in 2036

“Temperatures have been flat for 15 years—nobody can properly explain it,” the Wall Street Journal says. “Global warming ‘pause’ may last for 20 more years, and Arctic sea ice has already started to recover,” the Daily Mail says. Such reassuring claims about climate abound in the popular media, but they are misleading at best. Global warming continues unabated, and it remains an urgent problem.

The misunderstanding stems from data showing that during the past decade there was a slowing in the rate at which the earth's average surface temperature had been increasing. The event is commonly referred to as “the pause,” but that is a misnomer: temperatures still rose, just not as fast as during the prior decade. The important question is, What does the short-term slowdown portend for how the world may warm in the future?

The Intergovernmental Panel on Climate Change (IPCC) is charged with answering such questions. In response to the data, the IPCC in its September 2013 report lowered one aspect of its prediction for future warming. Its forecasts, released every five to seven years, drive climate policy worldwide, so even the small change raised debate over how fast the planet is warming and how much time we have to stop it. The IPCC has not yet weighed in on the impacts of the warming or how to mitigate it, which it will do in reports that were due this March and April. Yet I have done some calculations that I think can answer those questions now: If the world keeps burning fossil fuels at the current rate, it will cross a threshold into environmental ruin by 2036. The “faux pause” could buy the planet a few extra years beyond that date to reduce greenhouse gas emissions and avoid the crossover—but only a few.

A Sensitive Debate
The dramatic nature of global warming captured world attention in 2001, when the IPCC published a graph that my co-authors and I devised, which became known as the “hockey stick.” The shaft of the stick, horizontal and sloping gently downward from left to right, indicated only modest changes in Northern Hemisphere temperature for almost 1,000 years—as far back as our data went. The upturned blade of the stick, at the right, indicated an abrupt and unprecedented rise since the mid-1800s. The graph became a lightning rod in the climate change debate, and I, as a result, reluctantly became a public figure. In its September 2013 report, the IPCC extended the stick back in time, concluding that the recent warming was likely unprecedented for at least 1,400 years.

Although the earth has experienced exceptional warming over the past century, to estimate how much more will occur we need to know how temperature will respond to the ongoing human-caused rise in atmospheric greenhouse gases, primarily carbon dioxide. Scientists call this responsiveness “equilibrium climate sensitivity” (ECS). ECS is a common measure of the heating effect of greenhouse gases. It represents the warming at the earth's surface that is expected after the concentration of CO₂ in the atmosphere doubles and the climate subsequently stabilizes (reaches equilibrium).

The preindustrial level of CO₂ was about 280 parts per million (ppm), so double is roughly 560 ppm. Scientists expect this doubling to occur later this century if nations continue to burn fossil fuels as they do now—the “business as usual” scenario—instead of curtailing fossil-fuel use. The more sensitive the atmosphere is to a rise in CO₂, the higher the ECS, and the faster the temperature will rise. ECS is shorthand for the amount of warming expected, given a particular fossil-fuel emissions scenario.

It is difficult to determine an exact value of ECS because warming is affected by feedback mechanisms, including clouds, ice and other factors. Different modeling groups come to different conclusions on what the precise effects of these feedbacks may be. Clouds could be the most significant. They can have both a cooling effect, by blocking out incoming sunlight, and a warming effect, by absorbing some of the heat energy that the earth sends out toward space. Which of these effects dominates depends on the type, distribution and altitude of the clouds—difficult for climate models to predict. Other feedback factors relate to how much water vapor there will be in a warmer atmosphere and how fast sea ice and continental ice sheets will melt.

Because the nature of these feedback factors is uncertain, the IPCC provides a range for ECS, rather than a single number. In the September report—the IPCC's fifth major assessment—the panel settled on a range of 1.5 to 4.5 degrees Celsius (roughly three to eight degrees Fahrenheit). The IPCC had lowered the bottom end of the range, down from the two degrees C it had set in its Fourth Assessment Report, issued in 2007. The IPCC based the lowered bound on one narrow line of evidence: the slowing of surface warming during the past decade—yes, the faux pause.

Many climate scientists—myself included—think that a single decade is too brief to accurately measure global warming and that the IPCC was unduly influenced by this one, short-term number. Furthermore, other explanations for the speed bump do not contradict the preponderance of evidence that suggests that temperatures will continue to rise. For example, the accumulated effect of volcanic eruptions during the past decade, including the Icelandic volcano with the impossible name, Eyjafjallajökull, may have had a greater cooling effect on the earth's surface than has been accounted for in most climate model simulations. There was also a slight but measurable decrease in the sun's output that was not taken into account in the IPCC's simulations.

Natural variability in the amount of heat the oceans absorb may have played a role. In the latter half of the decade, La Niña conditions persisted in the eastern and central tropical Pacific, keeping global surface temperatures about 0.1 degree C colder than average—a small effect compared with long-term global warming but a substantial one over a decade. Finally, one recent study suggests that incomplete sampling of Arctic temperatures led to underestimation of how much the globe actually warmed.

None of these plausible explanations would imply that climate is less sensitive to greenhouse gases. Other measurements also do not support the IPCC's revised lower bound of 1.5 degrees C. When all the forms of evidence are combined, they point to a most likely value for ECS that is close to three degrees C. And as it turns out, the climate models the IPCC actually used in its Fifth Assessment Report imply an even higher value of 3.2 degrees C. The IPCC's lower bound for ECS, in other words, probably does not have much significance for future world climate—and neither does the faux pause.

For argument's sake, however, let us take the pause at face value. What would it mean if the actual ECS were half a degree lower than previously thought? Would it change the risks presented by business-as-usual fossil-fuel burning? How quickly would the earth cross the critical threshold?

A Date with Destiny: 2036
Most scientists concur that two degrees C of warming above the temperature during preindustrial time would harm all sectors of civilization—food, water, health, land, national security, energy and economic prosperity. ECS is a guide to when that will happen if we continue emitting CO₂ at our business-as-usual pace.

I recently calculated hypothetical future temperatures by plugging different ECS values into a so-called energy balance model, which scientists use to investigate possible climate scenarios. The computer model determines how the average surface temperature responds to changing natural factors, such as volcanoes and the sun, and human factors—greenhouse gases, aerosol pollutants, and so on. (Although climate models have critics, they reflect our best ability to describe how the climate system works, based on physics, chemistry and biology. And they have a proved track record: for example, the actual warming in recent years was accurately predicted by the models decades ago.)

I then instructed the model to project forward under the assumption of business-as-usual greenhouse gas emissions. I ran the model again and again, for ECS values ranging from the IPCC's lower bound (1.5 degrees C) to its upper bound (4.5 degrees C). The curves for an ECS of 2.5 degrees and three degrees C fit the instrument readings most closely. The curves for a substantially lower (1.5 degrees C) and higher (4.5 degrees C) ECS did not fit the recent instrumental record at all, reinforcing the notion that they are not realistic.

To my wonder, I found that for an ECS of three degrees C, our planet would cross the dangerous warming threshold of two degrees C in 2036, only 22 years from now. When I considered the lower ECS value of 2.5 degrees C, the world would cross the threshold in 2046, just 10 years later [see graph on pages 78 and 79].

So even if we accept a lower ECS value, it hardly signals the end of global warming or even a pause. Instead it simply buys us a little bit of time—potentially valuable time—to prevent our planet from crossing the threshold.

Cautious Optimism
These findings have implications for what we all must do to prevent disaster. An ECS of three degrees C means that if we are to limit global warming to below two degrees C forever, we need to keep CO₂ concentrations far below twice preindustrial levels, closer to 450 ppm. Ironically, if the world burns significantly less coal, that would lessen CO₂ emissions but also reduce aerosols in the atmosphere that block the sun (such as sulfate particulates), so we would have to limit CO₂ to below roughly 405 ppm.

We are well on our way to surpassing these limits. In 2013 atmospheric CO₂ briefly reached 400 ppm for the first time in recorded history—and perhaps for the first time in millions of years, according to geologic evidence. To avoid breaching the 405-ppm threshold, fossil-fuel burning would essentially have to cease immediately. To avoid the 450-ppm threshold, global carbon emissions could rise only for a few more years and then would have to ramp down by several percent a year. That is a tall task. If the ECS is indeed 2.5 degrees C, it will make that goal a bit easier.

Even so, there is considerable reason for concern. The conclusion that limiting CO₂below 450 ppm will prevent warming beyond two degrees C is based on a conservative definition of climate sensitivity that considers only the so-called fast feedbacks in the climate system, such as changes in clouds, water vapor and melting sea ice. Some climate scientists, including James E. Hansen, former head of the nasa Goddard Institute for Space Studies, say we must also consider slower feedbacks such as changes in the continental ice sheets. When these are taken into account, Hansen and others maintain, we need to get back down to the lower level of CO₂ that existed during the mid-20th century—about 350 ppm. That would require widespread deployment of expensive “air capture” technology that actively removes CO₂ from the atmosphere.

Furthermore, the notion that two degrees C of warming is a “safe” limit is subjective. It is based on when most of the globe will be exposed to potentially irreversible climate changes. Yet destructive change has already arrived in some regions. In the Arctic, loss of sea ice and thawing permafrost are wreaking havoc on indigenous peoples and ecosystems. In low-lying island nations, land and freshwater are disappearing because of rising sea levels and erosion. For these regions, current warming, and the further warming (at least 0.5 degree C) guaranteed by CO₂ already emitted, constitutes damaging climate change today.

Let us hope that a lower climate sensitivity of 2.5 degrees C turns out to be correct. If so, it offers cautious optimism. It provides encouragement that we can avert irreparable harm to our planet. That is, if—and only if—we accept the urgency of making a transition away from our reliance on fossil fuels for energy.

This article was originally published with the title "False Hope."

http://www.scientificamerican.com/article/earth-will-cross-the-climate-danger-threshold-by-2036/

Mario Molina et al., PNAS (2009), Reducing abrupt climate change risk using the Montreal Protocol and other regulatory actions to complement cuts in CO2 emissions

Proceedings of the National Academy of Sciences (October 12, 2009), doi: 10.1073/pnas.0902568106

Reducing abrupt climate change risk using the Montreal Protocol and other regulatory actions to complement cuts in CO2 emissions

Mario Molina, Durwood Zaelke, K. Madhava Sarma, Stephen O. Andersen, Veerabhadran Ramanathan and Donald Kaniaru

Abstract

Current emissions of anthropogenic greenhouse gases (GHGs) have already committed the planet to an increase in average surface temperature by the end of the century that may be above the critical threshold for tipping elements of the climate system into abrupt change with potentially irreversible and unmanageable consequences. This would mean that the climate system is close to entering if not already within the zone of ‘‘dangerous anthropogenic interference’’ (DAI). Scientific and policy literature refers to the need for ‘‘early,’’ ‘‘urgent,’’ ‘‘rapid,’’ and ‘‘fast-action’’ mitigation to help avoid DAI and abrupt climate changes. We define ‘‘fast-action’’ to include regulatory measures that can begin within 2–3 years, be substantially implemented in 5–10 years, and produce a climate response within decades. We discuss strategies for short-lived non-CO2 GHGs and particles, where existing agreements can be used to accomplish mitigation objectives. Policy makers can amend the Montreal Protocol to phase down the production and consumption of hydrofluorocarbons (HFCs) with high global warming potential. Other fast-action strategies can reduce emissions of black carbon particles and precursor gases that lead to ozone formation in the lower atmosphere, and increase biosequestration, including through biochar. These and other fast action strategies may reduce the risk of abrupt climate change in the next few decades by complementing cuts in CO2 emissions.

Link: http://www.pnas.org/content/early/2009/10/09/0902568106.full.pdf+html