Posts Tagged ‘climate change’

Climate change is real, we are causing it, and it is happening right now

June 14, 2011

A thundering open letter from the Australian scientific community has been published on “The Conversation”, as the start of a two-week series on climate science and “skeptics”:

The overwhelming scientific evidence tells us that human greenhouse gas emissions are resulting in climate changes that cannot be explained by natural causes.

Climate change is real, we are causing it, and it is happening right now.

Like it or not, humanity is facing a problem that is unparalleled in its scale and complexity. The magnitude of the problem was given a chilling focus in the most recent report of the International Energy Agency, which their chief economist characterised as the “worst news on emissions.”

Limiting global warming to 2°C is now beginning to look like a nearly insurmountable challenge.

Like all great challenges, climate change has brought out the best and the worst in people.

A vast number of scientists, engineers, and visionary businessmen are boldly designing a future that is based on low-impact energy pathways and living within safe planetary boundaries; a future in which substantial health gains can be achieved by eliminating fossil-fuel pollution; and a future in which we strive to hand over a liveable planet to posterity.

At the other extreme, understandable economic insecurity and fear of radical change have been exploited by ideologues and vested interests to whip up ill-informed, populist rage, and climate scientists have become the punching bag of shock jocks and tabloid scribes.

Aided by a pervasive media culture that often considers peer-reviewed scientific evidence to be in need of “balance” by internet bloggers, this has enabled so-called “sceptics” to find a captive audience while largely escaping scrutiny.

Australians have been exposed to a phony public debate which is not remotely reflected in the scientific literature and community of experts.

Beginning today, The Conversation will bring much-needed and long-overdue accountability to the climate “sceptics.”

For the next two weeks, our series of daily analyses will show how they can side-step the scientific literature and how they subvert normal peer review. They invariably ignore clear refutations of their arguments and continue to promote demonstrably false critiques.

We will show that “sceptics” often show little regard for truth and the critical procedures of the ethical conduct of science on which real skepticism is based.

The individuals who deny the balance of scientific evidence on climate change will impose a heavy future burden on Australians if their unsupported opinions are given undue credence.

And don’t miss this excellent article by Karl Braganza who describes in as few words as realistically possible how we know that we are warming up the earth:

fundamental understanding of the physics of radiation, combined with our understanding of climate change from the geological record, clearly demonstrates that increasing greenhouse gas concentrations will inevitably drive global warming. (…)

It’s now practically certain that increasing greenhouse gases have already warmed the climate system.

That continued rapid increases in greenhouse gases will cause rapid future warming is irrefutable.

Different approaches to the climate problem

May 16, 2011

The approach people take to climate change varies widely. They can be distinguished e.g. by the importance they place on climate change (or trust placed in the science), and by the conditions they put on potential solutions or response strategies. This gives rise to four different response strategies to the problem, along two axes:

Some archetypical responses for each quadrant are laid out in this cartoon:

(*): To which the German Coastguard in need of English language training replies: “What are you sinking about?” Cartoon adapted from Jip Lenstra.

There are of course loads of varieties possible here. Some contrarians may say: The water looks pretty nice. Some scientists (and so called “merchants of doubt”) are in fact saying: We’re thinking (and are not sure what’s happening. Let’s wait and see). Libertarians may say that life boats commissioned by the government are not to be trusted. And some greens may dream up a world of mermaids.

There are some interesting dynamics between the different archetypes: Most arguments happen in the horizontal direction (belief vs disbelief in an impending climate catastrophe; trust vs distrust of climate science; liking vs disliking certain lifeboats), whereas most liaisons occur in the vertical (between people who share the same (dis-)belief in climate change, but differ in the restrictions they place on response strategies).

Arguments on the science occur between the two upper panels: Is the boat sinking? Arguments on the response strategy often occur in the realm of the lower two panels: What restrictions (if any) do we place on the lifeboats? Are other agenda’s playing a role (besides wanting to save our souls)? Sometimes, the lower two panels actually partner up, like in those cases where they share a dislike for a certain lifeboat (CCS for example). Naturally, if you’re on a sinking boat most people will let go of any restrictions. Perhaps we can turn that around: The more restrictions people place on the lifeboat, the less severe they apparently think the problem is (in comparison with other issues).

If you think the boat can’t sink (upper left), then it doesn’t make sense to invest in a life-boat (lower left). Unless you like the lifeboat for another reason, e.g. for energy independence or to avoid peak oil. That would be a typical lower left panel response: You want a specific boat, but you don’t care much about climate change. Burning coal is perfectly fine according to this mindset. If OTOH you think the boat is sinking (upper right), then it makes sense to get a life boat (lower right).

The reverse is also happening (much to the detriment of the discussion): Some people have such a strong dislike for the lifeboat (lower left), that they therefore deny that the boat is sinking (upper left). Others like green lifeboats so much (lower right), that they shout out loud that the boat is sinking (upper right) without actually understanding how or why or when. They are prone to exaggerating the problem.

These styles of argument (from bottom to top) basically argue the science as a proxy for what the disagreement is really about: Liking or disliking certain boats.

Gotta love analogies…

Commentary on US Committee hearing on climate change

March 31, 2011

There’s yet another congressional hearing on climate change today in the US, featuring

Dr. J. Scott Armstrong, Professor, The Wharton School, University of Pennsylvania

Dr. Richard Muller, Professor, University of California, Berkley and Faculty Senior Scientist, Lawrence Berkeley Laboratory

Dr. John Christy, Director, Earth System Science Center, University of Alabama in Huntsville

Mr. Peter Glaser, Partner, Troutman Sanders, LLP.

Dr. David Montgomery, Economist

Dr. Kerry A. Emanuel, Professor, Massachusetts Institute of Technology

Real time commentary will be provided by several mainstream climate scientists to put the expected spin in context (see e.g. this commentary on Christy’s previous testimony a few weeks ago):

Live commentary by Trenberth, Dessler and Yohe (more info on this here)

Live blogging by Gavin Schmidt, Jay Gulledge and Eli Kintisch

Since it’s been getting quite popular lately for politicians to debate and try to legislate scientific understanding (am I the only one who finds this weird? No, no), SkS set up a special page with climate myths from politicians to try and keep them accountable for spewing nonsense:

Climate Myths from Politicians

 

Biodiversity, extinction and climate change

February 19, 2011

The previous thread turned into a discussion on how climate change might affect biodiversity. It started with Jeff Id’s taunt:

A warmer world will produce more food, biodiversity and a nice place for people and critters to live. Polar bears might be mad, but life is hard.

Aftersome back and forth’s, with e.g. Dave H noting the apparent disconnect between a strong focus on uncertainty and such a strong statement about positive effects, ecologist Jeff Harvey chimed in:

high temperatures are not a pre-requisite for high biodiversity

He points out that an important factor for maintaining high genetic and species richness is

stability – that is, that conditions in a region are not altered frequently by some important extrinsic challenge, such as rapid local climatic changes. (…)

the current rate of warming threatens to seriously undermine the functioning of biomes and ecosystems through uneven effects on species within tightly interacting food webs. (…)

Our species has simplified the planet biologically through the combined effects of paving, ploughing, damming, dredging. logging. slashing and burning, mining, dousing in synthetic pesticides, biologically homogenizing (e.g. through invasive species), altering the chemical composition of the air and water, and through various other forms of pollution. We know that genetic diversity is being lost at rates unseen in 65 million years, and against this background we are challenging an already impoverished fauna and flora to respond to climate changes that are unprecedented in perhaps tens of thousands of years.

Jeff Id replies:

I think like so many tied up in the eco-sciences you have blended too many causes and effects together to attribute the micro-warming to anything damaging to the ecosystem. (…)

my point is that over the next hundred years of warm weather, it would certainly result in higher planetary biomass all other effects unconsidered. Higher biomass eventually results in higher diversity. Warm in general is good for the planet, if you do it slowly enough and not too much of it.

How fast and how much, we could argue all day.

I tried condensing Harvey’s points thus:

- Biodiversity depends more strongly on the rate of change of climate than on the actual climatic state (i.e. whether “warm” or “cold”).

- That is consistent both with evidence from the past and with theoretical considerations

- Biodiversity is already being stressed (by multiple anthopogenic stressors, of which climate change is one), and this stress is likely to increase as (the rate of) climate change will increase. (i.e. future projected biodiversity loss is much stronger than current biodiversity loss)

Of course, it’s a bit more cpmplicated than that, as Harvey aludes to in his reply. Later on he notes that

The IUCN (…) does not classify a species as being ‘formally’ extinct until it has not been recorded in the wild for at least 50 years.

And on the current rate of extionction:

We KNOW that between 10 and 40% of well-known species (vascular plants and vertebrates) are threatened with extinction.

This is an area that don’t know much about, so I don’t have much to add. It’s a very important aspect though, especially when taking into account that projected future (rates of) warming are much stronger than what we’ve seen so far. Not to mention that once a species is lost, it’s lost practically forever. I would think that the rate of species loss can be much greater than the maximum rate of new species development (or creation if you wish ;-).  

References on biodiversity, extinction and climate change:

Extinction risks from climate change

Coral decline threatens fish biodiversity

Papers on ecosystem response to past climate change

Kate at Climatesight on extinction and climate

Association between global temperature and biodiversity, origination and extinction in the fossile record

Recommended reading by Jeff Harvey

Past, present and future temperatures

February 2, 2011

Check out these two graphs of past, present and future climate change:

They both provide a compelling visual picture of potential future warming in the context of past temperatures.

I wanted to use one of these graphs for a climate presentation recently, and there are pro’s and cons to each. Most importantly (to me):

- The bottom figure includes the “constant composition” scenario (C3 in yellow), which I find a useless distraction. It has no realistic value, as it implies an abrupt and arbitrary CO2 emission reduction, but continued aerosol emissions. (Aerosol particles have a short atmospheric residence time, so emissions have to be sustained in order to keep the concentration constant. OTOH, CO2 has a very long lifetime and with roughly 70% lower emissions its concentration would remain constant). It shows the amount of unrealized warming, but it most definitely is not an (even remotely) plausible scenario, and thus should not be presented as such.

- As for the proxy temperatures going back to the Middle Ages (or even further), I prefer the (mini) spaghetti graph of the lower figure over the top figure, which features only the Mann et al (2008) reconstruction.

Steve Easterbrook reminded me of my dilemma with his post comparing the top figure with one on which the bottom figure is based. He notes a few other differences:

- Different scenario’s are used in each (e.g. the top fig includes the “fossil intensive” A1FI (sort of business as usual) scenario, whereas the bottom fig doesn’t. A2 is worst case shown in the bottom graph, whereas it’s the middle of the road in the top graph.)

- Different temperature baseline (pre-industrial versus 1995-2004 period)

The top figure is from the Copenhagen Diagnosis; the bottom figure from Chapman and Davis (2010).

I chose to show the top graph, mainly because of the bothersome inclusion of the C3 “scenario” in the other one.

2010 blog round-up

January 3, 2011

I started writing this blog in mid 2008, and it was off to a quiet start. In the last months of 2009 and the start of 2010, my blog traffic gradually increased due to me chiming in on popular blog discussions on topics such as the CRU email affair or criticizing some contested ‘skeptic’ or ‘lukewarmer’.

A big change in my readership occurred in March 2010, after I wrote a post comparing different datasets of global average temperature. I was looking for a good looking graph of the major surface temperature reconstructions for use in a presentation, and after I couldn’t find one to my liking decided to prepare my own.

Now in all honesty, it wasn’t my pretty graphs that drew thousands of visitors to check out that post, but rather the verbal antics of pseudonymous commenter “VS”. It was initially picked up by Bishop Hill (causing a massive traffic spike) from where it spread to WUWT, Josh’s cartoons and others. It garnered over 2000 comments, many of which consisted of cheering VS on in his attempt to show that the increase in global average temperature could be described by a random walk (from which he later seemed to backpedal), based on a near unit root in the timeseries. But besides the expected chorus of “see, it’s all a scam/random/don’t touch my SUV!”, which got on my nerves at times, it was an interesting discussion from which I learned a thing or two. Of course, from energy balance considerations it is quite clear that the global average temperature can’t randomly walk away in any one direction without being somehow “forced” to. But I do have this desire to understand where someone else is coming from, to search for a nucleus of truth amidst the rhetoric, and to see if common ground can be reached between reasonable people who disagree.

I did a recap of this discussion in various posts thereafter (though never a proper round-up regretfully): Here, here, and my favorite: a sarcastic analogy on April fools day, followed by part 2 (not half as funny).

My site stats clearly show this post is an outlier: 45,000 views, whereas all the others are below 3000. After the big spike was over, the number of pageviews stabilized on a level a few times higher than before (~3000/week after vs ~700/week before). I think a lot of this increased traffic is due to more lively discussions taking place in the comment threads. The number of pageviews in 2010 were almost 10 times that in 2009, and in 2008 it averaged less than 100/week.

Since my recent posts are published in whole on the front page, the number of pageviews of separate posts sais more about the popularity of the discussion ensuing in the comment thread than of the head post itself (most of my pageviews are to the frontpage). That said, after the global avg temp thread the top-3 most popular discussions were:

The risk of postponing corrective action to a gradually deteriorating situation (2713)

The NIPCC report: don’t be fooled (2712)

Scott Denning to ICCC Heartland ‘conference’ gathering: “Be skeptical… be very skeptical!”  (2378)

The NIPCC post (from 2009) is popular because it’s one of the only rebuttals of their 2009 “climate change reconsidered” document, and as such is easy to find by google. The others were mainly popular because of the ensuing debate I think, though I like the post featuring Scott Denning’s excellent Heartland presentation a lot.

I don’t think these were necessarily my best posts; I’ll try to make a list of those some time later this week. Suggestions welcome, as I’m curious to hear what my readers liked or disliked.

It is clear though, even from my own blog, that antagonism sells. Posts where I’m sharply critical of something or someone tend to be more popular than thoughtful essays. Others have similar experiences I believe. Which goes to show that for many, blogs are mostly about entertainment and polarization. The challenge is to get some thoughtful reflection, discussion and critical thinking in there too.

A happy, thoughtful and fun new year everyone!

Technology and solutions

November 9, 2010

To avoid other threads from being overriden by discussions on technology issues, here’s a semi-open thread for those topics.

A few references:

Mark Jacobson’s review of solutions to global warming, air pollution, and energy security, comparing electric, hydrogen (both from a variety of primary energy sources) and biofuel powered transport.

SkepticalScience moving into solutions. John Cook captures my own sentiment very well: “My views on various solution strategies are not as well formed as my views on the attribution of climate change.” Lots of learning to do. Their first post leans heavily on the idea of stabilization wedges by Pacala and Socolow.

There are tons of documents outlining strategies to achieve a low carbon economy. E.g. Roadmap 2050 from the European Climate Foundation, I discussed the Shell energy scenario’s previously, IPCC wgIII, . I’ll update this list when I have more time on my hands.

Joe Romm has a lot of useful things to say about sustainable technologies (as even noted Joe Romm critic Tom Fuller admits). To avoid getting stuck in the details or in overly adversarial posts, perhaps best to go to an overview post such as this or that first.

Previous posts of mine somewhat related to technology and/or solutions. Some other threads also evolved into interesting technology discussions, but I can’t locate them at the moment (which shows the use of keeping discussions on topic).

Topics on my to-write-about list regarding technologies are geoengineering (based on e.g. chapter 6 from my hand in this report, which starts with an overview of mitigation options before exploring some in more detail), the indirect land use effect of biomass (e.g. chapter 3.3. of the same report) and perhaps transport.

IPCC history and mandate

October 1, 2010

The purpose of the IPCC was to assess the state of knowledge on the various aspects of climate change including science, environmental and socio-economic impacts and response strategies.

I.e. it was meant to report on and asses the scientific knowledge. This includes the question of how much evidence and (as a result) how much agreement amongst experts (consensus) there is for human induced climate change.

Some science historians point to other important aspects of IPCC’s history. The National Academy of Sciences wrote in 1979:

A plethora of studies from diverse sources indicates a consensus that climate changes will result from man’s combustion of fossil fuels and changes in land use.

Oreskes shows that the IPCC was set up in response to the emerging consensus in the 70’s/80’s that global warming due to GHG emissions would likely become a problem.

Spencer Weart writes:

The concern [about impending climate change] gave rise to the IPCC.

And also points to the Reagan administration being in favor of the clumsy IPCC approach, hoping that it would downplay the scientists’ fears.

When pointing to scientists who disagree with the IPCC consensus, it is important to note that people can agree in basically two directions. The survey by Brown, Pielke Sr and Annan for example shows this to be an approximate bell curve: Most (45-50%) of the respondents (scientists) more or less agree with the main thrust, and sizeable minorities (15-20%) think that IPCC overstated or understated its case. I discussed this survey and the broader question of why the consensus matters before. And I probably will pick this up again soon.

Scientifically, the more uncertain areas are the most interesting. However, if I look at the political decision making in terms of emission reductions and knowledge of the big picture (and the length of time that we’ve known about this big picture, albeit in gradually more certain terms), I can’t but conclude that the politics is hopelessly lagging behind the scientific knowledge in taking this problem seriously. (see e.g. my Dutch post “tijd voor de politiek om wetenschap serieuzer te nemen”.) Of course I’m aware that there’s more that informs politics than just the science, but still, there seems to be an uncomfortably big disconnect there. Stark warnings from science are ignored at our peril.

At this point in time, the uncertainties are pretty much irrelevant for policymaking, because any realistic change in the uncertain details is not going to affect the main trust of what we know, and thus the policy response that people may favour. For the long term, of course we need to finetune our knowledge, so research is still needed. (Hey, I’m a scientist, so I kind of have to say that, right?)

As Herman Daly said:

“Focusing on them [the big picture of what we know] creates a world of relative certainty, at least as to the thrust and direction of policy.” On the other hand, focusing on the more uncertain rates and valuations creates “a world of such enormous uncertainty and complexity as to paralyze policy”.

Perhaps that’s indeed what’s happening now, also cf. Judith’s uncertainty monster and complexity monster.

“To make the point more simply, if you jump out of an airplane you need a crude parachute more than an accurate altimeter.”

Funny how Daly and Curry both address the huge issues of uncertainty and complexity and arrive at diametrically opposed strategies of dealing with them. In terms of public communication, I’m with Daly.

From the principles governing IPCC work:

The role of the IPCC is to assess on a comprehensive, objective, open and transparent basis the scientific, technical and socio-economic information relevant to understanding the scientific basis of risk of human-induced climate change, its potential impacts and options for adaptation and mitigation.

IPCC reports should be neutral with respect to policy, although they may need to deal objectively with scientific, technical and socio-economic factors relevant to the application of particular policies.

Funnily enough, a commenter at Judith’s, Paul in Sweden, took this as proof of a “blatantly biased agenda”. Which is a little strange in light of the history of climate science and of the IPCC as mentioned above. Its mandate is a consequence of the scientific evidence for human induced climate change having become increasingly strong and societally relevant. It doesn’t state what the conclusion ought to be –it has to follow the science-, but of course it states what it’s supposed to assess.

Judith Curry also seems to suggest that the IPCC reports are working towards a predetermined conclusion, when she claims that they are akin to a legal brief (meant to persuade). If true, that should be reflected by large differences between the scientific evidence and the IPCC reports, and between scientists’ opinions and the IPCC reports.  I have not seen evidence of either.

Tom Curtis made some very thoughtful comments on the consensus thread at Judith’s, e.g.

In other words, the IPCC was tasked with reporting the consensus view of the science, were such a consensus existed; and to explain and report the differing opinions where no such consensus existed. Whether they have done that is not best judged by whether they have explained and included the opinions of every crackpot fringe group with an axe to grind on global warming; nor even those of every climatologist, no matter how small a number might support their views. Rather, they are to be judged by the agreement between the IPCC reports and the known consensus and divergences of scientific opinion.

Fortunately, we have available several anonymous surveys of the scientists opinions, which show conclusively that the IPCC reports fairly represent the consensus of relevant scientists on those topics on which it reports. (…)

The purpose of IPCC is to provided as succinctly as possible the best possible scientific advice for policy deciders to operate on. If they were required to consider all and every idea on climate change that circulates on the blogosphere; then the resulting document would be to large, and to ill organised to be usefull as a guide to policy.

Nevermind that the politicans still wouldn’t have a clue as to what is more likely true. The science has to be assessed and weighted; that is what makes the IPCC process useful. There already is another outlet for every crackpot idea out there (NIPCC report); it doesn’t need to be done by the IPCC as well.

To quote the Dutch newspaper “Volkskrant” again:

its work has political implications, but that that doesn’t mean that it’s engaged in doing politics.

And since I discussed history as well, see also my first blog post where I described the IPCC process. I don’t think anyone has read it yet, so I’d be much obliged. And while doing self-promotion, I kind a like this oldie featuring Fred Singer.

Judith Curry on anthropogenic versus natural causes of global warming

September 20, 2010

As most will know by now, Judith Curry has started her own blog, Climate Etc. In a recent post entitled “doubt” she said some things that highly surprised me. Basically, she claims equal evidence for anthropogenic forcing and natural variability being responsible for “most of the observed increase in global average temperatures since the mid-20th century”:

As an example, my personal weights for the Italian flag are:

1. white 40% [uncertainty and unknowns]

2. green 30%, [evidence for anthropogenic forcing]

3. red 30%. [evidence against anthropogenic forcing]

Before posting this, I had an email conversation with Judith Curry about these issues (so as to minimize any misunderstanding on my part). She wrote back (reprinted with permission):

I think you are misunderstanding what the IPCC actually says.  The statement says MOST (>50%) of the warming can be attributed to  anthropogenic, with an confidence of very likely (>90%).    My balance of 50-50 is a hair outside the IPCC range (which could include 51-49), and 1% difference is in the noise here.   Most can imply 51% or 90%.   I will be discussing the issue of attribution at length in a future point.  But my main point in the doubt post is the size of the white area, which is bigger than 5-10% IMO.

So she would translate the IPCC statement in the Italian flag style as anywhere between

white: 10 -1

green: 46 – 89

red: 44 – 10

Her own estimate is not that far off (in terms of the ratio between green and red) from the most conservative IPCC statement (where “most” means “just a bit more than half”), except having a much greater estimate of the uncertainty (which is her main point). So she seems to interpret red and green as portions attributable to anthropogenic and natural forcing, whereas initially I had interpreted them as evidence for the statement at hand versus evidence against. Both makes sense, but both are different. Also, one could claim that the IPCC statement encapsulates the uncertainty in the fairly wide “most of the warming”, i.e. it could still span a wide range, allowing for plenty of uncertainty. Similar as say, the weather in a week’s time is very uncertain, but I can still say that it’s very likely to be in between zero and thirty degrees C (being late september in Holland). These different interpretations make me doubt the usefulness of the Italian flag symbol to aid in clarifying (dis-)agreements.

Judith also claims equal evidence / equal portions of attribution for her “litmus test question”:

Will the climate of the 21st century will be dominated by anthropogenic warming (green) or natural variability (solar, volcanoes, natural internal oscillations)?

which is the question with the greatest policy relevance, IMO.  My scores on this one are

green 25%

white 50%,

red 25%.

This is astounding. I interpret this as claiming equal evidence pointing to natural variability being dominant over the next 90 years as compared to anthropogenic forcing. Or alternatively, an equal portion of 21st century climate change being attributable to human induced warming as to natural variability.

I’ve read quite a few “skeptical” papers that attempt to blame the warming on natural processes, and even if you’d take them as face value (even though in most cases they haven’t stood up to scrutiny), their collective body of evidence is a molehill compared to the mountain of evidence pointing to the dominance of anthropogenic forcing.

In a comment, Judith points to a blog post at Skeptical Science, with graphs of several natural forcings (solar) and cycles (PDO, ENSO) for the past 25-30 years. They exerted a slight cooling effect over this period. In contrast, CO2 exerted a strong warming effect, and indeed, the temperature has gone up. That hardly qualifies as equal amounts of evidence pointing to the warming being natural versus anthropogenic.

For future warming, her pronouncement is even stranger. In all plausible scenario’s, greenhouse gas concentrations will continue to rise for at least another few decades; in a business as usual scenario for many more to come. What natural forcing or variability could plausibly rival this relentlessly rising anthropogenic forcing in magnitude? Is there evidence at all for that being plausible? If so, is that evidence really as large as the evidence showing that greenhouse gas forcing will exceed the likely bounds of natural variability (if it hasn’t already)?

Take a look at how the global average temperature has varied over the past 130 years (yearly averages with 11 year running mean in bold):

An indication of unforced natural variability is given by the year to year variation, amounting to 0.1 to 0.2 deg C on a yearly basis. As the Skeptical Science article shows, natural forcings can not explain the most recent warming, because they don’t exhibit a trend of the needed direction or magnitude.

Now let’s stipulate that it’s all due to longer term natural variation (as opposed to a forcing) of an unspecified kind. What would that mean for the planetary energy balance? If internal variations would have been responsible for most of the planetary warming, the earth would be emitting more energy to outer space than it receives, resulting in a negative radiative imbalance at the top of the atmosphere (or the energy would have to come from other parts of the earth’s system).

Neither is the case. It’s actually opposite: There is a positive radiation imbalance and other reservoirs (e.g. oceanscryosphere) are also gaining more energy.

And then we haven’t even looked into the future yet. I recently posted this graph of two scenario’s that plausibly bracket a business as usual trajectory (red) and a stringent emission reduction trajectory (blue). The measured temperature increase up to now (which according to most scientists is strongly impacted by anthropogenic emissions) is given by the black line.

Judith’s estimates for the 21st century come down to a chance of warming of 0.25 + 0.75/2 = 0.625 versus a chance of cooling of 0.375, assuming natural factors having a 50% chance of either warming or cooling. So she deems the chance of warming to be roughly twice that of cooling, presumably even in a BAU scenario. Too bad that’s too long of a timeframe to place a climate bet on.

Look at how much the red -and even the blue- projections will likely deviate from the recent temperatures. I sure hope that there will be some magical counteracting cooling effect, but I haven’t seen any plausible evidence for such.

Postscript: From our email conversation, I understand her point of view better than before. But unlike the statement about the 20th century warming, which is not as far off from the IPCC as I had initially thought (except for the amount of uncertainty), her statement about the projected 21st century warming is hard for me to square with the mainstream scientific view, for which there is lots of evidence.

Extreme weather and climate change

August 18, 2010

It is an ill-posed question whether the 2003 heatwave was caused, in a simple deterministic sense, by a modification of the external influences on climate—for example, increasing concentrations of greenhouse gases in the atmosphere—because almost any such weather event might have occurred by chance in an unmodified climate. However, it is possible to estimate by how much human activities may have increased the risk of the occurrence of such a heatwave.

This is from a 2004 article in Nature about the European heatwave of 2003. The same can probably be said about the Russian heatwave of 2010. Arguing about whether this was ‘caused’ by AGW doesn’t make sense, unless you clarify carefully what you really mean.

A single weather event can not be attributed one-to-one to an external forcing of the climate. But the chance of occurrence can. Therefore it is in principle possible to say something about the relative likelihood of a certain extreme event in an unperturbed climate versus that in a human-perturbed climate. Or, to put it differently, to assign a certain portion of the blame/causality to the external forcing.

The return period for European heatwaves: Human influence has increased the chance of occurrence 9 fold. Figure from a 2008 presentation by Myles Allen (slide nr 24).

Weather is not climate. But of course they are related. In fact, climate change is a consequence of the weather changing over time. Due to changes in the planetary energy balance the chance of certain weather conditions changes. Over time this becomes apparent as a change in the mean weather: The climate has then observably changed. You cannot have climate change without changes in the weather.

Nielsen-Gammon has a good article about how to deal with these attribution issues related to single weather events. (h/t Judith Curry over at Kloor’s)

In between these two extremes, where AGW in a sense causes everything and AGW changes the probabilities but doesn’t in a sense cause anything in particular, there are, I think, two possibilities for ways in which we can assign a portion of the blame to AGW if appropriate.

The first way is to consider the direct effect of AGW on the mean state of the atmosphere, and consider that change to the mean state as AGW’s contribution to individual weather events. I’ll call this the “additive effect” approach. (…)

So, for example, temperatures in large parts of Russia are averaging 6 C or more above normal. At this point, climate change (from all anthropogenic causes), according to best estimates, has produced about 1 C of warming in the area. So it would be fair to say that man has turned what would have been a 5 C heat wave into a 6 C heat wave. Climate change has added one degree to the heat wave.

This sounds like a small impact, but it’s not appropriate to attribute 1/6 of the impacts to anthropogenic climate effects. Deaths, fires, and the like increase nonlinearly with the severity of a heat wave, so anthropogenic effects have made this heat wave lots more than 20% more severe than it would have been otherwise.

(This is meant to be an illustration, not a rigorously quantitative attribution.)

The second way is to consider the estimated effect of AGW on the probability of extreme events. I’ll call this the “probabilistic approach”. (…)

For extreme events, we want to know how often a certain threshold is crossed. (…)

So, to correctly say that an individual event was likely caused by AGW, its probability of occurrence would need to have increased, because of AGW alone, by a factor of 3 or more over pre-AGW conditions.

(bold in original; “likely” in the IPCC sense refers to 67% to 90% chance, hence the factor of 3)

Michael Tobis puts the question as follows:

“Is the average time between persistent anomalies on this scale anywhere on earth in the undisturbed holocene climate much greater than a human lifetime?” In other words, is this so weird we would NEVER expect to see it at all?

There are two approaches to answering this question. One is statistical (mathematical), and the other is integrative (based on experience and expertise rather than number-crunching).

He also summarized his position nicely in a comment at Kloor’s:

Stopping at “attribution of causality of individual events  is impossible” is not strong enough for the recent astonishing situation in Asia. “We are absolutely certain this couldn’t have happened in an undisrupted atmosphere” is too strong (…)

Why claim it is so unusual? Three reasons 1) this is an uncommonly stable and long-lived pattern (those are not good) 2) this is an uncommonly intense pattern, dipping all the way to the monsoon zone and fraternizing with the monsoon, to Pakistan’s great detriment and 3) the really big events tend not be in summer and not to be centered on hot spots but on cold spots. In other words, this blocking event has features dramatically different form other ones we have seen.

From ClimateCentral:

While there’s overwhelming observational evidence showing that humans are affecting climate, this evidence comes from long-term trends, rather than individual events.

Extreme events are related to climate change, however: the odds of them happening are much greater with climate change. (…)

We can estimate probabilities, but rarely can it be asserted with 100 percent confidence that there is a causal relationship between variables.

Tom Yulsman has an interesting article based on an interview with Peter Stott. What struck me though was Steve Bloom’s comment, comparing the manner in which doctors talk about the health risks of smoking versus how climate scientists talk about the climatological risks of greenhouse gas emissions. See also this pointy comment by SecularAnimist. Doctors tend to be much more upfront about the risks than climate scientists are (see also my previous post).


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