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Two Key Climate Change Concepts Are ‘Misunderstood’

There is widespread confusion about the near-term benefits of reducing greenhouse gas emissions, and that misunderstanding may be complicating the formidable task of reducing manmade global warming, argue two climate researchers in Science in a story published Thursday.

The scientists, Damon Matthews of Concordia University in Montreal and Susan Solomon of MIT, make the case that policymakers, the media, and to some extent the public have misunderstood the implications of two key concepts — the “irreversibility” of climate change, and the amount of global warming already in the pipeline due to historical greenhouse gas emissions.

The duo challenge what they say have become pervasive misinterpretations of recent scientific results, including findings from a 2010 National Research Council report they helped write that said that the amount of global warming to date is essentially irreversible on the timescale of about 1,000 years. That study has been repeatedly cited by policymakers to justify delays in tackling carbon emissions by making global warming appear to be inexorable, regardless of what actions are taken.

But Matthews and Solomon rebut that justification, writing instead that, “the irreversibility of past changes does not mean that future warming is unavoidable.”

In addition, they said the notion that global warming would continue to take place even if the amount of greenhouse gases in the atmosphere were to be frozen at current levels — rather than increasing year-after-year as they are now — has also helped justify inaction.

These findings have “been misinterpreted to mean that the rate of increase in Earth’s global temperature is inevitable, regardless of how much or how quickly emissions decrease,” the Science article said.

In an interview, Matthews said that confusion over the irreversibility and the amount of future warming that is already baked into the climate system has been widespread, and is serving to overcomplicate the global-warming issue, which is already challenging. “Anything that makes the problem seem more complicated than it is, is disempowering I think,” Matthews said.

“Over the years, I keep hearing both scientists and certainly policymakers talk about future warming, particularly near-term future warming, as if it is inevitable or predetermined by emissions that we’ve already put into the atmosphere,” Matthews said. “That’s actually a misinterpretation” of the published research, he said, since future warming depends mainly on future emissions, leaving the ball squarely in the court of policymakers.

“There will be future warming, but it’s because of human actions. It’s not because of the climate system itself,” Matthews said. “Future emissions are what’s driving future warming.”

Trend in observed atmospheric carbon dioxide concentrations as measured at the Mauna Loa Observatory in Hawaii.
Click on the image to enlarge. Credit: NOAA.

If emissions are cut, that means that future warming will be reduced. If not, then future warming will be higher. It’s as simple as that, Matthews said.

For example, “freezing” the amount of greenhouse gases in the air at current levels — about 397 parts per million — would require massive emissions cuts from present emissions trajectories, but the emissions that would continue would still contribute to global warming, Matthews said.

In other words, freezing carbon dioxide concentrations in the atmosphere at a particular level, such as 350 parts per million, — the target of the environmental advocacy group — is not the same thing as eliminating all emissions.

In reality, neither scenario is likely anytime soon. Given recent global emissions trends, with rapidly increasing emissions from developing countries like China and India and a lack of sharp emissions cuts from the industrialized world, a freeze in atmospheric carbon concentrations is nowhere in sight, let alone a shutdown of all emissions, and a massive global effort would be needed to reverse course.

Matthews said that if emissions were reduced significantly in the near term, global warming would also be reduced over that time period, although it might not be detectable given the presence of natural climate variability.

Gavin Schmidt, a climate scientist at NASA’s Goddard Institute for Space Studies in New York, said that near-term actions to reduce emissions wouldn’t have a noticeable impact on the climate system for many years. “The fact remains that plausible near-term actions to reduce emissions are not going to have a detectable impact on trends for a couple of decades,” he said in an interview. 

The Science article said the critical factor determining future warming is “societal inertia,” rather than the inertia of the climate system, since actions taken now will determine the amount of emissions in the next few decades, and thereby determine how much additional global warming is likely to take place. “The future is within our hands. The amount of climate warming will be whatever we make it. We have not yet committed ourselves to anything particular other than by lack of action,” Matthews said.

Energy infrastructure such as coal-burning power plants, oil refineries, and pipelines are built to last several decades, so decisions made today regarding the building of such plants will affect emissions for many years to come.

Katharine Hayhoe, a climate scientist at Texas Tech University who was not involved in the Science article, said the misconceptions that Matthews and Solomon set out to correct are more common, and more problematic, among policymakers than in the general public. She said she thinks the main message that emerges from the article is a hopeful one.

“It is often said — and I have said it myself — that a certain amount of change is inevitable. As the authors point out, that is largely because of the inertia in our energy systems that do not allow us to rapidly transition from carbon-emitting to carbon-free sources,” she said in an email. “This sad fact can make us feel like any action is futile. Reality, however, is very different: action is necessary, possible, and important. To me, that's the main point of this paper.”

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By dan_in_illinois
on March 28th, 2013


Was the global warming that has occurred in the distant past also been reversible?  If it was, then how did it get reversed so that we now have a decent climate once again?  If it wasn’t the same type of “irreversible” warming, why?

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By mememine69 (54434)
on March 28th, 2013

Understand this:
*Science can say a comet hit is real but can’t say a climate change crisis is as real as a comet hit.
*Find us just one IPCC warning that isn’t qualified with “maybe”.
*Science has NEVER said any crisis “WILL” happen in 27 years, only “maybe”, never eventual or imminent or…..
*Occupywallstreet does not even mention CO2 in its list of demands because of the bank-funded carbon trading stock markets ruled by corporations and politicians.
*Science gave us pesticides.
If science ever says a climate crisis is as certain as a comet hit, count me in. “MAYBE” isn’t good enough for real planet lovers. We don’t WANT this misery to be real for our children.

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By Yooper49855
on March 28th, 2013

@ dan_in_illinois:  Atmospheric CO2 levels are now 100 points higher than at any point in the past 600,000 years.  The last time CO2 levels were this high the Arctic and Greenland had no ice, sea levels were 70 feet higher and mammals such as camels thrived in the Arctic.

Looking backwards in the paleo record, the nearest comparison to the ongoing rise in CO2 and temperatures occurred during the PETM extinction 55 million years ago.  Except that the current rise in temperatures and CO2 is happening more than 10 times faster than during that PETM extinction event.

To “reverse” the ongoing AGW-caused climate change will require a complete cessation of fossil fuel emissions and about a hundred thousand years of hard rock chemical weathering; provided we stop our business-as-usual emissions trajectory.

Changing the atmospheric composition of our atmosphere has consequences.

Welcome to the Age of Consequences.

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By MikeH
on March 29th, 2013

@ dan_in_illinois

Read Jeff Masters precis of Dr Richard Alley’s AGU talk “The Biggest Control Knob: CO2 in Earth’s Climate History”

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By Eric Peterson (Front Royal, VA 22630)
on March 29th, 2013

The “pipeline” is mentioned at the beginning but not thereafter.  The pipeline is a century to millennium-scale process caused by the oceans. Where ocean-bottom water resurfaces it generally causes cooling because the deep ocean is only a few degrees C.  The global warming from CO2 that is sent to the deep ocean is warming that water a bit.  If it resurfaces it will still cause cooling and only a small amount less cooling.  So the pipeline will not supply any warmth for the next few centuries, the only time scales we care about.  For all intents and purposes, there is no pipeline.

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By Yooper49855
on March 29th, 2013

@ Eric Peterson:  the oceanic warming doesn’t depend on a full-mixing cycle time to warm the world (note that warmer-than-usual water going down also means that upwelling water will eventually likewise be warmer-than-usual).  The lag in thermal response to surface warming is currently in the 25-50 year range.  This means a multidecadal lag in response by the oceans to the incremental warming from the sun.

The reality is, our climate has built up 423,239,835 Hiroshima bombs worth of accumulated heat since 2005 (Levitus 2012).  Recent research shows that this sequestration of energy into the oceans is increasing, as the forcing from human activities (fossil fuel-derived CO2).  Per Balmaseda, Trenberth, and Källén (2013): 

“Aside from the volcanic cooling episodes, there is an additional cooling episode following the huge 1997–98 El Niño event after 1998, which mainly affects the upper 700 m. The event led to a global warming of the atmosphere and made 1998 the warmest year on record to that point as heat came out of the ocean, largely through evaporative cooling [Trenberth et al., 2002]. After 1998, there was a rapid exchange of heat between the regions above and below 700 m (Figure S01 in suplementary material). The heat exchange between the layers above and below 700 m during 1998 is consistent with a recent study based on Argo data for more recent events [Roemmich and Gilson, 2011]. Then after 1999 the warming starts again dramatically, this time also involving all depth ranges. This signals the beginning of the most sustained warming trend in this record of OHC. Indeed, recent warming rates of the waters below 700 m appear to be unprecedented.”

Note, too, that including the Argo data increases the global energy imbalance:
“The magnitude of the warming trend is consistent with observational estimates, being equivalent to an average 0.47 ± 0.03 W m-2 for the period 1975–2009. There is large decadal variability in the heat uptake, the latest decade being significantly higher (1.19 ± 0.11 W m-2) than the preceding record. Globally this corresponds to 0.84 W m-2, consistent with earlier estimates [Trenberth et al., 2009]. In an observing system experiment where Argo is withdrawn, the ocean heating for the last decade is reduced (0.82 ± 0.10 W m-2), but is still significantly higher than in previous decades.”

Meaning less short term warming at the surface…but at the expense of a greater earlier long-term warming, and faster sea level rise.

So the warming of the oceans is actually accelerating, not decreasing…

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By Robert Marston
on March 29th, 2013

I think that ‘confusion’ is simply being used by those who support continued high rates of emissions. Most arguments to the effect that ‘we can’t stop global warming so why try’ probably aren’t based in actual misunderstanding of the science, but moreso are just attempts to capitalize on it.

Nuances like this will confuse pretty much anyone who’s not following global warming on a day-to-day basis. So, yeah, it’s just people trying to capitalize on the confusion.

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By hank
on March 29th, 2013

An excellent example of a “Climate” meme gone wrong. While most people who follow the debate closely understand that the “AGW is irreversible” talk is just more of the “It’s worse than we thought” alarmism, your average ‘Joe’ on the street is thinking; “Why bother trying to do anything”.
There really needs to be a more standard message here. There are way too many people making way too many over-the-top claims about the perils of AGW that most people just don’t hear it anymore!

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By Bill Prindle (Charlottesville, VA 22902)
on March 29th, 2013

The greatest “hoax” perpetrated in the climate debate is the assertion that serious action to cut GHG emissions would be economically ruinous. This has been perpetrated through a small but influential band of economic modelers at CRA and elsewhere, who use Computable General Equilibrium (CGE) econometric models with algorithms written such than any technology substitutions come with large economic costs, starting at $50/ton of CO2 reduced or higher. When a model is based on such erroneous assumptions, they will show major economic damage. But those assumptions are wrong—energy efficiency and other clean energy technologies have lifecycle costs lower than the fossil fuels they would replace, such that they provide net economic benefits. The CRA CGE types will not admit this, and the James Inhofes continue to flack this unsound modeling to claim that climate action is costly. The truth is that climate action now is actually helpful to our economy—to say nothing about the non-climate environmental benefits that come with clean energy. That in itself is enough to justify clean energy policy action today.

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By Lewis Cleverdon
on March 29th, 2013

Well that’s clear as mud.

“Damon Matthews of Concordia University in Montreal and Susan Solomon of MIT, make the case that policymakers, the media, and to some extent the public have misunderstood the implications of two key concepts — the “irreversibility” of climate change, and the amount of global warming already in the pipeline due to historical greenhouse gas emissions.”

As reported, they appear to completely ignore critical issues around both key concepts.

On the supposed ‘irreversibility’ issue, the clear and obvious potentials for Carbon Recovery (to restore the pre-industrial atmosphere by 2100) and for Albedo Restoration (to restore the pre-industrial global SAT during this decade) are simply not mentioned. There is of course much to debate around both, starting with their indispensable roles in halting the untenable outcomes of GHG outputs (which the essential rapid Emissions Control cannot now achieve) and including the fact that both options require stringent collective supervision since either could be done very badly or for the wrong objective.
But to try to close down proper debate on these pivotal issues by proposing that Global Warming is irreversible on less than millennial timescales seems less than creditable.

Similarly their thoughts on the timelags issue, as reported, seems to lack central components of a proper clarification of the issue:
- Where for instance is the description of Ocean Thermal Inertia, and discussion of whether this should be either dismissed - or seen as a 25, 30, 35 or 40yr effective timelag on GHG outputs’ warming potential being realized ?
- Where is the outline of the unseen current warming, say from the albedo loss feedback, that is being locked in alongside anthro-GHG warming for say the 2050s ?
- Where is discussion of the other key timelagged factor, namely the rapid additional warming due to Emissions Control closing down our maintenance of the cooling ‘Sulphate Parasol’ ?

If these scientists are able to refute rather well-established understandings on both mitigation techniques and timelags, then why are some distinctly vague and rather generalized statements the best that can be reported of the arguments of their refutations ? For instance:
“Matthews said that if emissions were reduced significantly [by x] in the near term [by y] global warming would also be reduced [by z] over that time period, although it might not be detectable given the presence of natural climate variability.”



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By Karen Street (Berkeley, Ca 94703)
on March 29th, 2013

Much thanks!

I don’t understand the statement about 350. There was an analysis in PNAS 2009 by Solomon et al, same Solomon, saying that we aren’t going to see 350 again this millennium.

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By Dave (Basking Ridge, NJ 07920)
on March 29th, 2013

Lewis: “Well that’s clear as mud”.  Personally I couldn’t agree more.  After reading this I was thinking the same thing.

One thing seems to be missing from this discussion and has specifically to do with policy makers who do not understand by 2013 that climate change is an urgent issue requiring immediate strong action – which is really what it boils down to. This is maybe the 700 pound gorilla we are ignoring.  Policy makers are politicians. Perhaps, as suggested here, one reason is that some have erroneously and honestly concluded that the situation is so bad that there’s no point in doing anything now and so on. There can be other less honest reasons.

Lawmakers and policy makers tend to be lawyers. Good lawyers can be quite adept at quickly mastering and ‘interpreting’ complicated technical arguments whichever way their client wants them to.  So in that sense, and based on having tracked relevant events here, I would argue the ‘cynical’ view that notwithstanding the “honest” contingent, a significant number of other US policymakers have in fact been professionally fully engaged with this issue for some time as evidenced by the various highly effective blocking actions on climate change / clean energy legislation. And that to do that effectively requires a good working knowledge of all the arguments. Congressional lawmakers wishing to argue against climate change action will do so as lawyers citing whatever arguments support their case. A potential example is given in this report:

“That study has been repeatedly cited by policymakers to justify delays in tackling carbon emissions by making global warming appear to be inexorable, regardless of what actions are taken.”

In view of this and various known history concerning similar critical perceptions of the US governments decision making processes over key issues, I therefore suspect that when needed, healthy campaign contribution checks have likely helped far more to efficiently and rapidly clarify congressional leaders’ ‘understandings’ about climate change. In view of that consideration, I think that any discussion of the technical confusion specifically of policymakers over climate change and irreversibility needs also to address the means to first or otherwise address fundamental bias or predispositions whether those biases and predispositions are individually felt honestly or by proxy.

@Karen: Thanks for the reference. To your question re 350, I think the idea of committed global warming due to the long residence time of CO2 and the factors that impact that particular aspect would bear some mention here.

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By Gill Raker (Nogales, AZ 85621-3211)
on March 29th, 2013

— at this point, climate change is so politicized that it’s difficult for the general public to sort out what scientists really know—and don’t know—about it, and this pretentious article will only serve to climate activists and some deluded scientists to keep believing that the only way to preserve the Holocene climate humans are used to is to cut carbon dioxide atmospheric concentrations to 350 parts per million, last seen around 1988: that’s like the 70-year-old alcoholic saying, ‘I’m going quit drinking when I’m 60 years old’… don’t you think?

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By Brett Callaghan (Athens, OH 45701)
on March 31st, 2013

As an Environmental Studies student, I have noticed that misunderstanding of information is a widespread issue with Climate Change.  People do not realize the serious reality of the issue because they do not properly understand the science behind it.
“Matthews said that if emissions were reduced significantly in the near term, global warming would also be reduced over that time period, although it might not be detectable given the presence of natural climate variability.”
If the reduction in global warming is not detectable, then how will scientists and policy makers help people to believe in the policy makers’ ability to make policies that to have an effect in reducing global warming, and to understand what effects have been made?

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By William Hughes-Games (Waipara New Zealand 7447)
on April 2nd, 2013

Another misconception is the true strength of methane as a green house gas.  As long as it is being emitted at a steady rate over many decades, the 20 or 25 times as effective, comment is valid.  However, if the methane emissions increase as they are doing now,  a figure of more than 100 is more to the point.

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By Jez Hunter (London)
on April 4th, 2013

Just a small point. In the article I think you mistake greenhouse gases in the atmosphere (@397ppm) for co2 solely - that is what mauna loa graph next to the statement measures. Real ghg levels are much higher though the last figure i saw was a few years ago when it measured approx 417 ppm.
Otherwise thanks got the article.

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