Posts Tagged ‘global warming’

PBL survey shows strong scientific consensus that global warming is largely driven by greenhouse gases

August 4, 2015


(30 Aug 2015): US Presidential candidate Rick Santorum apparently made some erroneous statements about our survey when he was on the Bill Maher show. The source for his claims is probably Fabius Maximus’ blog discussed below. ATTP has a good post on the latest installment in this contuing saga.

(2 Sep 2015): Politifact did a fact-check on Santorum’s claim and found it to be false. Their article draws on input from a variety of experts and gives a very good overview of the issues involved.


As Michael Tobis rightly points out, the level of scientific consensus that you find “depends crucially on who you include as a scientist, what question you are asking, and how you go about asking it”. And on how you interpret the data. We argued that our survey results show a strong scientific consensus that global warming is predominantly caused by anthropogenic greenhouse gases. Others beg to differ. Recent differences of opinion are rooted in different interpretations of the data. Our interpretation is based on how we went about asking certain questions and what the responses indicate.

To quantify the level of agreement with a certain position, it makes most sense to look at the number of people as a fraction of those who answered the question. We asked respondents two questions about attribution of global warming (Q1 asking for a quantitative estimate and Q3 asking for a qualitative estimate; the complete set of survey questions is available here). However, as we wrote in the ES&T paper:

Undetermined responses (unknown, I do not know, other) were much more prevalent for Q1 (22%) than for Q3 (4%); presumably because the quantitative question (Q1) was considered more difficult to answer. This explanation was confirmed by the open comments under Q1 given by those with an undetermined answer: 100 out of 129 comments (78%) mentioned that this was a difficult question.

There are two ways of expressing the level of consensus, based on these data: as a fraction of the total number of respondents (including undetermined responses), or as a fraction of the number of respondents who gave a quantitative or qualitative judgment (excluding undetermined answers). The former estimate cannot exceed 78% based on Q1, since 22% of respondents gave an undetermined answer. A ratio expressed this way gives the appearance of a lower level of agreement. However, this is a consequence of the question being difficult to answer, due to the level of precision in the answer options, rather than it being a sign of less agreement.

Moreover, the results in terms of level of agreement based on Q1 and Q3 are mutually consistent with each other if the undetermined responses are omitted in calculating the ratio; they differ markedly when undetermined responses are included. In the supporting information we provided a table (reproduced below) with results for the level of agreement calculated either as a fraction of the total (i.e., including the undetermined answers) or as a fraction of those who expressed an opinion (i.e., excluding the undetermined answers), specified for different subgroups.

Verheggen et al - EST 2014 - Table S3

For the reasons outlined above we consider the results excluding the undetermined responses the most meaningful estimate of the actual level of agreement among our respondents. Indeed, in our abstract we wrote:

90% of respondents with more than 10 climate-related peer-reviewed publications (about half of all respondents), explicitly agreed with anthropogenic greenhouse gases (GHGs) being the dominant driver of recent global warming.

This is the average of the two subgroups with the highest number of self-reported publications for both Q1 and Q3. In our paper we discussed both ways of quantifying the level of consensus, including the 66% number as advocated by Tom Fuller (despite his claims that we didn’t).

Fabius Maximus goes further down still, claiming that the level of agreement with IPCC AR5 based on our survey results is only 43-47%. This result is based on the number of respondents who answered Q1b, asking for the confidence level associated with warming being predominantly greenhouse gas-driven, as a fraction of the total number of respondents who filled out Q1a (whether with a quantitative or an undetermined answer). As Tom Curtis notes, Fab Max erroneously compared our statement to the “extremely likely” statement in AR5, whereas in terms of greenhouse gases AR5 in Chapter 10 considered it “very likely” that they are responsible for more than half the warming. Moreover, our survey was undertaken in 2012, long before AR5 was available, so if respondents had IPCC in mind as a reference, it would have been AR4. If anything, the survey respondents were by and large more confident than IPCC that warming had been predominantly greenhouse gas driven, with over half assigning a higher likelihood than IPCC did in both AR4 and AR5.

PBL background report - Q1b

Let me expand on the point of including or excluding the undetermined answers with a thought experiment. Imagine that we had asked whether respondents agreed with the AR4 statement on attribution, yes or no. I am confident that the resulting fraction of yes-responses would (far) exceed 66%. We chose instead to ask a more detailed question, and add other answer options for those who felt unwilling or unable to provide a quantitative answer. On the other hand, imagine if we had respondents choose whether the greenhouse gas contribution was -200, -199, …-2, -1, 0, 1, 2, … 99, 100, 101, …200% of the observed warming. The question would have been very difficult to answer to that level of precision. Perhaps only a handful would have ventured a guess and the vast majority would have picked one of the undetermined answer options (“I don’t know”, “unknown”, “other”). Should we in that case have concluded that the level of consensus is only a meagre few percentage points? I think not, since the result would be a direct consequence of the answer options being perceived as too difficult to meaningfully choose from.

Calculating the level of agreement in the way we suggest, i.e. excluding undetermined responses, provides a more robust measure as it’s relatively independent of the perceived difficulty of having to choose between specific answer options. And, as is omitted by the various critics, it is consistent with the responses to the qualitative attribution question, which also provides a clear indication of a strong consensus. If you were to insist on including undetermined responses in calculating the level of agreement, then it’s best to only use results from Q3. Tom Fuller’s 66% becomes 83% in that case (the level of consensus for all respondents), showing the lack of robustness in this approach when applied to Q1.

Verheggen et al - Figure 1 - GHG contribution to global warming

Some other issues that came up in recent discussions:

See also the basic summary of our survey findings and the accompanying FAQ.


Responses to the Climate Science Survey

April 12, 2015

Appeared in similar form on the PBL website

In the Spring of 2012, the Netherlands Environmental Assessment Agency PBL held a survey among 1868 scientists studying various aspects of climate change, including physical climate, climate impacts, and mitigation. The main results of the survey were published in an article in Environmental Science and Technology (ES&T) in August 2014: “Scientists’ views about attribution of global warming”. It showed that there is widespread agreement regarding a dominant influence of anthropogenic greenhouse gases on recent global warming. This agreement is stronger among respondents with more peer-reviewed publications.

A background report with the results for all 31 questions has now been made available. The total number of responses for each answer option is provided and a subdivision into seven groups for five questions. The background report contains previously unpublished data. Some highlights are provided below.

Climate sensitivity

Respondents were asked for their opinion regarding the best estimate and likely range for equilibrium climate sensitivity (ECS). This is an important quantity for projections of global warming, as it gives the expected warming that would follow from a doubling in atmospheric CO2 concentration after the climate system has equilibrated to the new conditions. Thus, expected warming in the future depends on the combination of total emissions and climate sensitivity.

The figure below gives the average estimates of ECS from 7 groups of respondents, including authors of the Working Group I report of the fourth IPCC Assesment Report (AR4), respondents who signed public declarations critical of mainstream climate science as embodied by IPCC (‘unconvinced’), and four different subgroups distinguished according to their self-declared number of climate related peer-reviewed publications (0–3; 4–10; 11–30; more than 30). Results from most groups were very close to the IPCC range (1.5-4.5 °C) mentioned in the fifth assessment report (AR5) – except those tagged as ‘unconvinced’ which strongly deviated from the other groups, and to a lesser extent the group of respondents with three or less publications. For all subgroups the ‘best estimate’ was slightly lower than the ‘best estimate’ reported in AR4 (i.e. 3 °C). AR5 provided no best estimate.

Scientists views on climate sensitivity - PBL

Role of climate science in society

Respondents were also asked their opinion about seven statements regarding the role of climate science in society and how the science should be communicated. There was a strong consensus that scientists themselves should communicate with both policymakers and the general public about climate change and that communication with the general public should focus on solid knowledge. To a lesser extent there was agreement that risks and uncertainties should be emphasised during such communication. Responses varied more strongly about whether or not existing uncertainties in climate science strengthen the case for mitigation (i.e. to avoid potential low probability, high impact events). There was (strong) disagreement with the statement that climate science would be too uncertain to be useful for policymaking on climate change.

Scientists views on role of science in society - PBL

The role of the sun in global warming

In the public debate about climate change the role of the sun is often put forward as an alternative explanation for global warming. Question 17 asked what fraction of recent global warming could be attributed to the sun. Those tagged as ‘unconvinced’ had the lowest fraction of respondents that indicated that they don’t know (together with AR4 authors) and the highest fraction that said that the role of the sun is unknown. As expected they also had by far the highest fraction (27%) that believed that the sun caused more than half of recent global warming.

As with the attribution questions (see the ES&T article), there appears to be a trend in responses going from the group with fewest publications to those with most. The more publications about climate change respondents report to have written, the larger fraction of them agree with the IPCC position that the sun hardly played a role in recent global warming, since the solar output decreased slightly over that period.

Scientists views on the role of the sun in global warming - PBL

More information:

PS: I’ll have a poster presentation about the survey at the EGU conference this week, in session EOS6 “Communication and Education in Geoscience” on Thursday evening.

Climate researcher Bart Strengers wins wager with climate sceptic Hans Labohm

January 23, 2015

Guestpost by Bart Strengers. Originally appeared as a news item on the PBL website.

Late 2009, in the run-up to the international climate conference in Copenhagen, PBL climate researcher Bart Strengers had an online discussion with climate sceptic Hans Labohm on the website of the Dutch news station NOS (in Dutch). This discussion, which was later also published as a PBL report, ended in a wager. Strengers wagered that the mean global temperature over the 2010–2014 period would be higher than the mean over 2000 to 2009. Hans Labohm believed there would be no warming and perhaps even a cooling; for example due to reduced solar activity.

At the request of Labohm, it was decided to use the UAH satellite temperature data set on the lower troposphere (TLT) (roughly the lowest 5 km of the atmosphere). These data sets are compiled by the University of Alabama in Huntsville. Satellites are used to measure radiation in the atmosphere, after which the temperature of the various layers of the atmosphere is derived using a complex algorithm.

According to the UAH today, temperatures appear to have been an average 0.1 °C warmer over the past five years than over the 10 years before that. Thus, Strengers has won the wager. The stakes: a good bottle of wine.

PBL temp comp Eng - 0040_001g_adhoc
The UAH temperature series since 1979 (no satellites were available for the period before then). The green lines represent the mean over periods of 10 years. The purple line on the far right is the mean over the 2010–2014 period.
UAH satellite data series shows the greatest warming

Precisely these UAH data, incidentally, show by far the most warming. The 4 other main global temperature series also show warming over the last 5 years, but one that is markedly lower (between 0.03 and 0.05 °C).

What causes the differences between the data series?

The table below shows the global warming, in °C, over the past 5 years, compared to the 10 years before that, for the five main global temperature series: the satellite series of the University of Alabama in Huntsville (UAH) and of the Remote Sensing Systems (RSS), and the surface temperature series of NASA, Climate Research Unit (CRU) and the National Climatic Data Centre (NCDC). CRU’s series are based on surface temperature measurements up to and including November 2014, as data on December were not yet available.

The large difference (by more than a factor of 3!) between the UAH and RSS satellite series is remarkable (also see the graph below). According to the UAH team, in which two well-known climate sceptics are involved, the difference is mainly caused by the fact that RSS partly bases its series on an old satellite (NOAA-15) with an increasingly lower orbit around the earth. This causes an error in measurements that is insufficiently corrected by RSS. All in all, it is a technical and complex issue, which possibly causes the differences, but it mainly shows how complicated the procedure is for determining global temperatures on the basis of satellite measurements. The three surface measurement series provide a much more consistent image of between 0.04 °C and 0.05 °C warming.

Satellite temperature measurements difficult to compare with surface measurements

In addition, it is important to note that satellite and surface measurements are difficult to compare. This is due to the fact that satellite series are based on the temperature of the entire lower troposphere (the lowest 5 km of the atmosphere). The temperature of this atmospheric layer is, for example, much more sensitive to El Niños than surface temperatures are. This is illustrated in the graph below by the relatively high peak for the two satellite series at the time of the super El Niño in 1997–1998 and the less strong El Niño of 2010. The reverse is the case for La Niñas, such as the strong one of 2008; here, satellite series typically show a lower temperature.

PBL - temp comp - 0040_002g_adhoc
Temperatures according to 2 satellite series (UAH and RSS). The purple line indicates the mean of the three surface temperature series. The satellite series show peaks in 1998 and 2010, as a result of El Niño, which are greater than those in the surface temperature series. The low satellite value for 2008 coincides with the opposite of an El Niño: La Niña. Note how the last 4 years in the RSS series are far below those in the other series. According to the surface temperature measurements, 2014 was the warmest year on record!

The graph shows that the last years in the RSS series clearly deviate from the other temperature series, with lower values of over 0.1 °C. This suggests that RSS rather than UAH is too low (as also claimed by the UAH team). The outcome of this discussion may lead to adjustments to one or both satellite series, as has been done in the past, particularly to the UAH series, on numerous occasions.

The surface temperature series further indicate that 2014 was the warmest year on record, even without an El Niño!

Contribution by cooling and warming influences.

Strengers indicated at the time that ‘in light of the scientific uncertainties, I may lose, but this is not likely to happen’. He gave four reasons why a possible reduction in warming, or even a cooling could occur. Bold indicates that the related reason more or less became a reality over the past 5 years.

  • a continued (relatively) low solar activity;
  • a relatively high heat absorption by the (deep) oceans;
  • a period of cooling due to incidental variations in the climate;
  • lower climate sensitivity than expected.

In addition, Strengers gave three reasons why he nevertheless expected to win:

  • a further increase in greenhouse gas concentrations in the atmosphere;
  • the ‘best-estimate’ by the IPCC is that of a warming of 0.2 °C per decade;
  • the chances of overestimating climate sensitivity are smaller than those of underestimation.

The sum of all factors, thus, has led to continued warming. Below each of these factors is explained in more detail.

Continued (relatively) low solar activity

Over the past 5 years, the reduced solar activity has continued and, thus, likely also has slightly reduced global warming over that period. In the discussion at the time, Strengers wrote: ‘astrophysics […] cannot rule out the possibility of a long period of relatively low activity. This could lead to a reduction in warming of up to 0.4 °C (although 0.2 °C is more likely) over the coming 20 to 30 years.’ The past 5 years, therefore, are in keeping with the idea that such a period of relatively low activity is a fact, but the degree to which this reduction will actually continue over the coming years, or for how long it will go on, is still very uncertain.

Relatively high heat absorption by the (deep) oceans

Over 90% of the heat that is added to the climate system, particularly caused by the increase in greenhouse gases, ends up in the oceans. Only a few per cent is stored in the atmosphere. The remainder is absorbed by the land surface and ice sheets (which are therefore steadily melting). Variations in heat absorption can have a large impact on surface temperatures. According to a recent study by England et al., published in December 2013 in Nature, there has been increased heat absorption by the oceans since 2001, which since then has reduced warming by 0.1 to 0.2 °C. The added heat seem to be concentrated largely around the equator in the western part of the Pacific Ocean, at a depth of around 125 to 200 metres, which means it remains ‘hidden’ from the atmosphere. England and his team do not expect this heat storage effect to continue in this way and they project that, at a certain moment, temperatures at the surface level will begin to increase more rapidly. This could happen, for example, due to an El Niño with large amounts of heat being released suddenly, possibly causing temperatures to jump, as happened in 1997–1998 during the so-called super El Niño. Over the past months, a new El Niño seems to be developing. If this continues into 2015, this year may end up being even warmer than the record year of 2014.

A period of cooling due to incidental variations in the climate

The climate knows random variations. Strengers wrote that these may lead to longer periods of no warming or even cooling, even under a steady increase in greenhouse gas concentrations in the atmosphere. During the discussions, Strengers pointed to a study which shows on the basis of climate models that periods of up to 16 years of random cooling or non-warming may occur, even in an overall warming climate. Recent research shows that a combination of random factors likely has led to a reduction in temperature increases over the past 15 years (see the section below, ‘IPCC’s ‘best-estimate’ is that of a warming of 0.2 °C per decade’, for more details). However, this reduction in warming was not high enough for the past 5 years to be cooler than the decade before that.

Lower climate sensitivity than expected

The IPCC – the scientific body that inventories all knowledge on climate change every 5 to 7 years –stated in 2007 in its fourth assessment report (AR4) that climate sensitivity was likely (i.e. with a likelihood of 66%) between 2.0 and 4.5 °C, with a ‘best estimate’ of 3 °C. The fifth assessment report (2013) stated a range of 1.5 to 4.5 °C without giving a ‘best estimate’. The reason for the downward adjustment of the lower limit to 1.5 °C (at which it had been estimated since 1990) originated from a number of studies that pointed to the possibility of a low climate sensitivity. The ‘best estimate’ was not provided “because of a lack of agreement on values across assessed lines of evidence and studies” (i.e. based on all studies up to and including July 2012). All this, however, does not mean that climate sensitivity was ‘less than expected’. In fact, the only thing that can be concluded is that the value of climate sensitivity has become more uncertain.

Further increase in greenhouse gas concentrations in the atmosphere

Greenhouse gas concentrations in the atmosphere have steadily increased over the past 5 years. By late 2014, CO2 concentrations were at 399 ppm (399 molecules of CO2 per million molecules of air). Five years ago this level was 388 ppm. The increase is a direct result from an ever faster increase in CO2 emissions, particularly in countries such as India and China.

IPCC’s ‘best-estimate’ is that of a warming of around 0.2 °C per decade

At the time of IPCC’s fourth assessment report, in 2007, a global warming of 0.2 °C was assumed for the current decade (2010–2019), particularly on the basis of climate model results. As discussed above, the degree of warming according to the UAH series, which is based on satellite measurements, was 0.1 °C over the last 5 years, compared to the mean of the 10 years before that. If this trend continues over the coming 5 years, our current decade will register a warming of around 0.15 °C – slightly less than the ‘best estimate’, but well within the projected range by the IPCC. However, all surface temperature series show a lower degree of warming, between 0.04 and 0.05 °C, over the past 5 years (see the section on ‘What causes the differences between the data series?’). Extrapolation over the 2010–2019 decade shows a total maximum warming of 0.08 °C [typo fixed]. This is in line with the discussion on the ´hiatus´ or the finding that the rate of warming over the past 15 years has been lower than in the 20 years before that, and also lower than the average outcome of many climate models. Note though that there is no significant change in trend from 1998. If climate model calculations take into account the ´random factors´ that cannot be predicted, such as the occurrence of El Niños, solar activity, and volcano eruptions, then models and observations seem much more in agreement.

The chances of overestimating climate sensitivity are smaller than those of underestimation

The IPPC’s fifth assessment report (2013) states that climate sensitivity is likely (66% probability) to be between 1.5 and 4.5 °C. It subsequently states that it is extremely unlikely (less than 5% probability) to be smaller than 1, and very unlikely (less than 10% probability) to be higher than 6.  In other words, very low values are less likely than very high values, which substantiates the above statement.

[Note: hyperlinks added by Bart Verheggen]

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)


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?


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


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.


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.


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.


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