Posts Tagged ‘global warming’

Andrew Dessler’s testimony on what we know about climate change

January 19, 2014

In his recent testimony, Andrew Dessler reviewed what he thinks “are the most important conclusions the climate scientific community has reached in over two centuries of work”. I think that’s a very good choice to focus on, as the basics of what we know is most important, “at least as to the thrust and direction of policy” (Herman Daly). This focus served as a good antidote to the other witness, Judith Curry, who emphasizes (and often exaggerates) uncertainty to the point of conflating it with ignorance.

Dessler mentioned the following “important points that we know with high confidence”:

1.  The climate is warming.

Let’s take this opportunity to show the updated figure by Cowtan and Way, extending their infilling method to the entire instrumental period (pause? which pause?):

Cowtan and Way - Global Avg Temp 1850 - 2012

2. Most of the recent warming is extremely likely due to emissions of carbon dioxide and other greenhouse gases by human activities.

This conclusion is based on several lines of evidence:

- Anthropogenic increase in greenhouse gases

- Physics of greenhouse effect

- Observed warming roughly matches what is expected

- Important role of CO2 in paleoclimate

- No alternative explanation for recent warming

- Fingerprints of enhanced greenhouse effect (e.g. stratospheric warming cooling, which was predicted before it was observed)

Dessler:

Thus, we have a standard model of climate science that is capable of explaining just about everything. Naturally, there are some things that aren’t necessarily explained by the model, just as there’re a few heavy smokers who don’t get lung cancer. But none of these are fundamental challenges to the standard model.

He goes on to explain that the so-called “hiatius” is not a fundamental challenge to our understanding of climate, though it is “an opportunity to refine and improve our understanding of [the interaction of ocean circulation, short-term climate variability, and long-term global warming].”

What about alternative theories? Any theory that wants to compete with the standard model has to explain all of the observations that the standard model can. Is there any model that can even come close to doing that?

No.

And making successful predictions would help convince scientists that the alternative theory should be taken seriously. How many successful predictions have alternative theories made?

Zero.

3. Future warming could be large 

On this point I always emphasize that the amount of future warming depends both on a combination of factors:

- the climate forcing (i.e. our emissions and other changes to the earth’ radiation budget)

- the climate sensitivity (the climate system’s response to those forcings)

- the climate response time (how fast will the system equilibrates).

Internal (unforced) variability also plays a role, but this usually averages out over long enough timescales.

4. The impacts of this are profound.

In the climate debate, we can argue about what we know or what we don’t know. Arguing about what we don’t know can give the impression that we don’t know much, even though some impacts are virtually certain.

The virtually certain impacts include:

• increasing temperatures

• more frequent extreme heat events

• changes in the distribution of rainfall

• rising seas

• the oceans becoming more acidic

Time is not our friend in this problem.

Nor is uncertainty.

The scientific community has been working on understanding the climate system for nearly 200 years. In that time, a robust understanding of it has emerged. We know the climate is warming. We know that humans are now in the driver’s seat of the climate system. We know that, over the next century, if nothing is done to rein in emissions, temperatures will likely increase enough to profoundly change the planet. I wish this weren’t true, but it is what the science tells us.

Peter Sinclair posted a video of Andrew Dessler’s testimony. Eli Rabett posted Dessler’s testimony in full.

A key distinction in the two senate hearings was that Andrew Dessler focused on what we know, whereas Judith Curry focused on what we don’t know (though “AndThenTheresPhysics” made a good point that Curry goes far beyond that, by e.g. proclaiming confidence in certain benign outcomes (e.g. regarding sensitivity) while claiming ignorance in areas where we have a half-decent, if incomplete, understanding, e.g. regarding the hiatus). I have argued before that emphasizing (let alone exaggerating) uncertainties is not the road to increase people’s understanding of the issue, where what we do know is much more important to convey (if your goal is to increase the public understanding of scientific knowledge). Alongside that I argue that much more attention is needed to explain the nature of science, which is needed to e.g. place scientific uncertainties in a proper context.

CartoonUncertainty

Herman Daly said it as follows, in a quote I’ve used regularly over the past few years:

If you jump out of an airplane you need a crude parachute more than an accurate altimeter.

Arguing whether the altimeter might be off by a few inches is interesting from a scientific/technological perspective, but for the people in the plane it’s mostly a distraction.

Climate Science Survey – the questions

October 8, 2012

In the spring of 2012, a large scale climate science survey was held amongst 6500 scientists studying various aspects of global warming. The survey was spearheaded by the Netherlands Environmental Assessment Agency (PBL), where I was responsible for the execution and analysis during the first half of 2012.

The objective of this study is to gain insight into how climate scientists perceive the public debate on the physical scientific aspects of climate change. More info about the survey was posted on the PBL website at the time, which has recently been updated to include a link to the survey questionnaire. Please note that the survey is no longer active.

Some confusion has arisen over the status of this survey. I responded at WUWT in an attempt to clarify:

We undertook a survey in March/April of this year (which, as Hans Labohm mentioned in a comment on WUWT, had been previewed by a variety of people with different viewpoints). Some respondents, e.g. Timothy Ball, asked to see the questions again. After internal consultation, we decided to publish the survey questions on the institute’s website, so that they are viewable to all. We contacted the survey respondents to inform them of the questions being available to view. I informed Dr Ball of this as well, to follow-up on my earlier email to him.

Our email to all respondents, informing them of the fact that the survey questions are available on the web, was apparently misunderstood to mean that we were again soliciting responses to a survey; this is however not the case. Roger Pielke Sr had already put a notice about the survey on his blog, which he has since updated after an email clarifying that this is an inactive survey, to which he had previously responded.

Below we (Bart Verheggen and Bart Strengers) reply to some of the more substantive questions regarding the survey questions raised on WUWT. However, we will not discuss results or the survey sample at this point in time. We will do so when our manuscript has been accepted.

(more…)

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…

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

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.

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.

The problem is that it’s not our problem (but rather that of future generations)

September 6, 2010

Those who caused the problem are not the same as those who will carry the burden.

The more indirect the relation between their actions and the consequences, the lower the motivation to do something about it (consider e.g. the time lag between smoking and its health effects).

If someone causes a problem without having to bear the consequences themselves, their motivation to solve it becomes even smaller.

If those that are adversely affected can’t even hold you to account (e.g. because they aren’t born yet), it becomes tempting to not be bothered by the impending problem, even if you’re contributing to its cause.

There are not only equity issues with different parts of the world, but also with different generations: Intergenerational equity, an issue often mentioned by Jim Hansen. That is all the more pressing when you consider that our actions -or inactions- only take effect decades into the future:

Past and projected future temperature change under two scenario’s:

- Fossil intensive (SRES A1FI)

- Strong emission reductions (halved by 2050)

Note that the difference between strong emission reductions and fossil intensive becomes noticeable only after 3 decades or so: There are long time lags in the climate system.

It makes it so easy to say “it’s not our problem”…

Or is it?

Me and my daughter in the Polish Tatra mountains.

Figure above from Meinshausen et al., Nature 2009.

Recent changes in the sun, CO2 and global average temperature

April 11, 2010

Several times in recent weeks people have commented that the sun is responsible for the current climate change rather than CO2. Ironically, this was sometimes argued by the same people who were cheering on the claim that there is no deterministic forcing at work in driving temperatures upwards (be it GHG or the sun or whatever else). So much for coherence.

Let’s look at how the global average temperature, CO2 and the sun changed over recent decades:

Temperatures jiggle up and down, but are increasing over the longer term (multiple decades). CO2 has a seasonal cycle due to the ‘breathing’ of the biosphere, but is steadily increasing over the years due to human emissions. The sun shows an 11-year cycle, but no secular increase or decrease over this time period.

Let’s go a bit farther back in time (HadCRU temperatures up to 2008; number of sunspots as a proxy of solar activity; original here):

And looking back at sunspot observations over the past 400 years (original):

So what does this tell us? Of course changes in the sun affect our climate (coherence check: This implies a certain degree of determinism). Low solar activity (e.g. during the Maunder and the Dalton minima) played a role in the so called ‘little ice age’. In the beginning of the 20th century solar activity increased, which contributed to the warming (together with greenhouse gases and a lack of volcanic activity). However, since the solar output (including cosmic rays) remained steady (or even decreased a bit) since the 1950′s, it doesn’t seem very likely that the sun contributed to the recent increase in temperatures since the 1970′s. The little ice age ended (~1850) long before the recent warming started (~1975), so no causal relation there either.

The main reasons that disqualify the sun as being a major culprit in recent global warming are:

• No increase in solar output (or decrease in cosmic rays) over the past 50 years

• Nighttime temperatures increased more than daytime (inconsistent with solar forcing; consistent with GHG forcing)

• Stratospheric cooling (inconsistent with solar forcing; consistent with GHG forcing)

See also Skeptical Science and Lockwood’s recent review paper (the first chapter, describing the context of the ‘controversy’ is well worth reading).

Global average temperature increase GISS HadCRU and NCDC compared

March 1, 2010

I made some graphs of global temperature change according to the three major compilations based on measured surface temperatures: GISS, HadCRU and NCDC. They are expressed as the temperature difference (“anomaly”) with respect to the 1901-2000 average as the baseline.

Temperatures jiggle up and down, but the overall trend is up: The globe is warming.

To highlight the long term trend more clearly, below the same figure with in addition the 11 year running mean (which stops 5 years short of each endpoint for lack of data to calculate the mean):

Some people prefer you to only look at the last dozen of years:

Often, the last datapoint (representing 2009) is omitted, and only HadCRU temperatures (in blue) are shown, to create the most visually compelling picture for claiming that “global warming has stopped” or even reversed (“blogal cooling”, pun intended).

If however we look at the trend through the average of the three datasets over the period 1975-2009 (during which greenhouse gas forcing was the dominant driver of climate change), we see the following:

The trend over 1975 to 2009 is approximately the same (0.17 +/- 0.03 degrees per decade) for all three temperature series.

The error represents the 95% confidence interval for the trend, i.e. if you were to repeat the trend analysis a hundred times on the real underlying data, 95 times you would find that the trend is within the range 0.14 to 0.20 degrees per decade.

The thin black lines represent the 95% confidence “predictions bands” for the data: Based on the observed variability, 95% of the data are expected to fall within these lines.

The observed yearly variability in global temperatures (sometimes exceeding 0.2 degrees) is such that 10 years is too short to discern the underlying long term trend (0.17 degrees per decade). There is no sign that the warming trend of the past 35 years has recently stopped or reversed.

 More info:

A major difference between the datasets is that HadCRU omits the arctic (in effect assuming that is warms as the global average), while GISS estimates it by interpolation. I don’t know about NCDC. See also RealClimate and James Hansen.

Similar analysis of GISS, HadCRU and NCDC temperatures up to 2007 by Tamino. Other nifty analyses by Tamino relating to the same theme can be found here, here, here and here.

1998 was a record warm year in large part because of a very strong El Nino event. If the effect of the ENSO cycle is removed, the warming trend becomes even more apparent, see e.g. RealClimate. Other rebuttals of the spurious 1998-claim at SkepticalScience, Coby Beck, Zeke Hausfather, RealClimate, Scott Mandia, Greenfyre (including lots more links) and Peter Sinclair of the denial crock of the week youtube videoseries.

Four independent statisticians were given the data (up to 2008) and asked to look for trends, without being told what the numbers represented. Not surprisingly, they found no evidence of a downward trend. Story retold e.g. here and here.

Robert Grumbine explains the art of cherrypicking and why it is not science.

Update: If you want higher resolution versions of any of the figures here you can email me via the link on the right (under “pages”).


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