I’ve been away for a week (more about this later, maybe), so haven’t had a chance to post anything. It has been a fairly warm week here in the UK, so it’s seem worth mentioning a recent paper about the global risk of deadly heat. It’s been covered already by Carbon Brief, so I don’t need to say much (I’ll probably fail).

Credit: Mora et al. (2017)

A key point is illustrated in the figure on the right, which shows temperature and relative humidity. The black crosses shows temperature and relative humidity during events that were lethal. The blue line shows the likely boundary between lethal and non-lethal events, and the red line is a 95% probability threshold (which, I think, means almost certainly deadly). Our body (in fact, any mammal’s body) generates heat, and the ability to transfer that heat away depends on temperature and relative humidity, and there is a combination of temperature and relative humidity above which it is no longers possible to do so. As the paper says

The fact that temperature and relative humidity best predict times when climatic conditions become deadly is consistent with human thermal physiology, as they are both directly related to body heat exchange. First, the combination of an optimum body core temperature (that is, ~37<supoC), the fact that our metabolism generates heat (~100 W at rest) and that an object cannot dissipate heat to an environment with equal or higher temperature (that is, the second law of thermodynamics), dictates that any ambient temperature above 37oC should result in body heat accumulation and a dangerous exceedance of the optimum body core temperature (hyperthermia). Second, sweating, the main process by which the body dissipates heat, becomes ineffective at high relative humidity (that is, air saturated with water vapour prevents evaporation of sweat); therefore, body heat accumulation can occur at temperatures lower than the optimum body core temperature in environments of high relative humidity.

The Carbon Brief article does highlight some criticisms of this study (the available data did not cover all parts of the world, for example). However, it does seem clear that if we continue to emit CO2 into the atmosphere, we will continue to warm and a larger fraction of the world (and a larger fraction of the world’s population) will experience heatwave conditions (combinations of temperature and relative humidity) that could be deadly.

This is a key point, though. How these conditions will change in the future will depend on what emission (and, hence, concentation) pathway we actually follow. Climate change isn’t guaranteed to lead to a substantial increase in the probability of these conditions occuring; it largely depends on what we choose to do, or not do.

An adaptability limit to climate change due to heat stress (Sherwood & Huber 2009).

Posted in Climate change, Global warming, Science, Severe Events | Tagged , , , , , | 47 Comments

What does the Vostok ice core tell us?

Euan Mearns, who runs a blog called Energy Matters, had a post in 2014 about The Vostok ice core: Temperature CO2 and CH4. This post has apparently had 8000 reads, is probably one of the most read texts on the subject, and yet, according to this post,

the Climate Science community continues to ignore the fairly profound implications of what the data actually shows.

The key issue appears to be a lag between temperature changes and CO2/CH4 changes that led Eaun to conclude that

variations in CO2 and CH4 are both caused by global temperature change and freeze thaw cycles at high latitudes. These natural geochemical cycles makes it inevitable that CO2 and CH4 will correlate with temperature. It is therefore totally invalid to use this relationship as evidence for CO2 forcing of climate, especially since during the onset of glaciations, there is no correlation at all.


CO2 in the past played a negligible role. It simply responded to bio-geochemical process caused by changing temperature and ice cover.

I left a couple of comments, but only one has appeared, so I thought I would quickly write this post. The reason why the climate science community has probably ignored the profound implications in Euan’s posts is – I think – because they’re not really very profound. Firstly, this is data from a single site (Vostok). Even though greenhouse gases may be well-mixed, the temperature is not. You need to be a little careful when using this single site to infer something about global temperatures, and the relationship between temperature changes and CO2/CH4 changes. Maybe more importantly, though, what the data indicates is not really all that surprising.

It is certainly not the case that CO2 is the main driver of the glacial cycles. The trigger for the glacial cycles is probably orbital variations, in particular large changes in solar insolation at high northern latitudes. However, the net change in solar insolation (globally) is small, so it cannot – by itself – produce much in the way of warming/cooling. What is thought to happen is that these changes trigger either ice sheet retreat, or ice sheet advance (depending on whether we’re moving into a glacial, or out of a glacial). This changes the planetary albedo which produces either warming (ice sheet retreat) or cooling (ice sheet advance).

This warming/cooling then results in the release/uptake of CO2 from the oceans, and also influences vegetation (which itself produces an albedo change and releases, or takes up, CO2). The change in atmospheric CO2 (and CH4) then produces more warming/cooling, causes further retreat/advance of the ice sheets, and further changes in vegetation. These different processes (albedo changes and changes in atmospheric CO2/CH4) then together produce the temperature changes that move us into, or out of, a glacial period.

A key point is that CO2 does indeed respond to temperature changes (through ocean outgassing/uptake and changes in vegetation) and – in the context of the glacial cycles – is more properly a feedback, than a forcing. This, however, does not mean that it is not a greenhouse gas and that changes in its concentration in the atmosphere will not influence global temperatures (it clearly does). We really cannot explain the glacial cycle without including the influence of changes in greenhouse gas concentrations in the atmosphere.

This paper by James Hansen and Makiko Sato provides a nice explanation of the process and indicates that changes in atmospheric greenhouse gas concentrations (mainly CO2 and CH4) is responsible for about half of the glacial cycle temperature changes and that this is consistent with an equilibrium climate sensitivity of about 3oC ± 1oC. There are also a couple of nice Skeptical Science posts that discuss the whole CO2 lags temperature issue.

Of course, I’m not an expert on this, so may not have explained this as well as I could have. Also, maybe I have missed something and maybe what Euan Mearns has presented is indeed profound and should not be ignored by the climate science community. However, if I have learned something in my years as a research scientist; when you think you’ve discovered something profound and everyone else ignores it, maybe it really isn’t as profound as you initially thought.


Through the beauty of Twitter, people have provided some relevant references. Gavin Foster suggests that the newer West Antarctic Ice Sheet Divide Ice Core resolves some of the age issues. He also highlights this paper, the abstract of which says:

We show that although low-frequency CO2 variations parallel changes in Antarctic temperature, abrupt CO2 changes occur that have a clear relationship with abrupt climate changes in the Northern Hemisphere. …..We suggest that processes operating on centennial timescales, probably involving the Atlantic meridional overturning circulation, seem to be influencing global carbon-cycle dynamics and are at present not widely considered in Earth system models.

and this paper (which is discussed – I think – in the Skeptical Science posts I highlighted), the abstract of which says:

Differences between the respective temperature changes of the Northern Hemisphere and Southern Hemisphere parallel variations in the strength of the Atlantic meridional overturning circulation recorded in marine sediments. These observations, together with transient global climate model simulations, support the conclusion that an antiphased hemispheric temperature response to ocean circulation changes superimposed on globally in-phase warming driven by increasing CO2 concentrations is an explanation for much of the temperature change at the end of the most recent ice age.

Steve Forden also highlighted a paper that says:

The robust lead of Antarctic temperature over CO2 concentration during several recent glacial–interglacial transitions inferred from the Antarctic ice cores apparently contradicts the concept of CO2-driven climate change and still remains unexplained……….our results provide an explanation for the observed Antarctic temperature lead over CO2 concentration. It is shown that the interhemispheric oceanic heat transport provides a crucial link between the two hemispheres. We demonstrate that temporal variations of the oceanic heat transport strongly contribute to the observed phase relationship between polar temperature records in both hemispheres……Based on our results, we argue that the analysis of leads and lags alone, without a comprehensive understanding and an adequate model of all relevant climate processes, cannot provide direct information about causal relationships in the climate system.

And another couple of papers, thanks to Twitter. Does seem as though this isn’t really being ignored.

Eric Steig (who is one of the PIs of the WAIS Divide Ice Core) has highlighted a couple of other papers in this comment. In particular, Pedro et al. (2012), which says:

we show that the increase in CO2 likely lagged the increase in regional Antarctic temperature by less than 400 yr and that even a short lead of CO2 over temperature cannot be excluded. This result, consistent for both CO2 records, implies a faster coupling between temperature and CO2 than previous estimates, which had permitted up to millennial-scale lags.

There are also two Realclimate posts that cover this issue, and another Skeptical Science post.

Posted in Climate change, Climate sensitivity, ClimateBall, Global warming, Greenhouse effect, Pseudoscience, Research, Science | Tagged , , , , , | 57 Comments


Peddling is arguably the most favorite way for contrarians to lob factoids behind enemy lines. Once a door opens, peddlers block it with their foot and dispatch their sale pitches. Peddled talking points seldom matter to the topic at hand, i.e. they’re red herrings, or as I prefer to call them squirrels, because “look, squirrel!,” because the verb squirreling,  and because Rachel.

Responding to the peddler’s talking point only opens other doors. A flurry of squirrels get thrown on the field, exchanges go in many directions at the same time. At best we get constructive brainstorming, at worse a food fight. In any event, the Gods of ClimateBall (tm) rejoice.

Since language is a martial art, peddling can start anywhere and about anything. I recently experienced one with Freedom Fernando, after I dared to retweet a tweet telling that that some were burning food in Brazil. Fernando’s peddling move was his famous “but Venezuela”:

My response abides by the principle: A Squirrel for a Squirrel.  It also conveys that I don’t mind discussing the historical reasons why many South American countries became allergic to the Washington Consensus. I could have pointed out that famines correlated more with mismanagement and political conflicts than ideology, but baiting Fernando with a Marxian source was too tempting. At least twenty-seven tweets followed. There could have been more, but I decided to write this instead.

Fernando doubled-down his peddling by denying that Venezuela had economic sanctions. In return, I cited an official webpage of the US Government describing these. Then it got interesting.

A Think Tank Tie (see the mug face below) chimed in to say that the sanctions did not target Venezuela per se, but individuals. My first response recalled that this point was an ignoratio elenchi:

As if warning against doing business in Venezuela wasn’t a most effective way to put economic pressure on a country. (Many hold that official sanctions are inefficient at best.) As if the Iran sanctions couldn’t affect Venezuela. As if there wasn’t any underhanded ways to expand one’s country’s influence. As if any of this was relevant to my point anyway.

Then it gets surreal: Fernando accuses me of backing up a genocide. A genocide, no less. Qui ne dit mot consent, I suppose, so I reject his accusation and call him on his peddling. Instead of owning it, Fernando doubles down by blaming me for having provoked his peddling!

To show Fernando that I could not care less about ideology, I showed him the historical prices of oil between 2008 and 2014. The correlation between low oil prices and increase in Venezuelian suffering should be obvious to anyone. Our Think Tank Tie resurfaces, moving the goalpost using a “what about question.” I remind him of whataboutism while clarifying that the chart wasn’t meant as an explanation of the crisis:

Our Think Tank Tie then gets personal, which backfires quite quickly since he can’t commit to the crap his think tank peddles. Nevertheless, Fernando’s peddling succeeded. Squirrels were thrown. Nothing got resolved. Everybody left happy.

THE END? No, not at all. Like auditing, peddling never ends.

Posted in ClimateBall, Freedom Fighters | Tagged , , | 58 Comments

Climate communication

Doug McNeall recently gave a talk about surviving the climate communication environment, which he discusses in this post. A lightly edited version of the slides are available here. The slides, of course, don’t tell you precisely what was said in the talk, but I find little to disagree with. The environment can be difficult and challenging; we should try to say interesting things but also be careful of what we say; it should be relevant but not too complex; we should know the audience, and we should repeat the message.

One thing I will say is that Doug’s slides illustrate the apparent conflict between the deficit model and the cultural congnition model. I think such a conflict does exist, but I’ve never been sure why it needs to exist. It seems that there are some who are pre-disposed to reject certain information and that it’s extremely difficult to communicate effectively with such people if they don’t identify with you in some way. Therefore, some people (Katherine Hayhoe, for example) can be more effective communicators in some situations, and we should – in my opinion – encourage and support those who are capable of reaching people who might preferentially reject the information that’s being presented. However, this doesn’t mean that there is no place for those who simply see themselves as presenting information, rather then explicitly trying to reach certain groups. I don’t see a good reason why the deficit model and cultural congnition couldn’t be seen as complementary, rather than in conflict.

However, Doug’s post highlighted that some (mainly female scientists) are choosing to no longer engage on social media because of the harassment that they receive. This isn’t simply it being unpleasant, but is a level of harassment that is genuinely disturbing and that noone should be expected to endure. Doug asks what can be done about this, and I don’t have any good answers; it’s something that really shouldn’t happen, but clearly does. I also find it difficult to comment on something I’ve never experienced, and almost certainly will never experience.

All I can think of suggesting is based partly on a series of tweets from Jacquelyn Gill. Maybe we should try to continually remind ourselves that science communication can be difficult, that we can all do better, but that we should also try to support those who are engaging publicly and – when appropriate – promote what they’re doing. This doesn’t mean not correcting people when they make a mistake, or not suggesting ways in which they could do better; we just need to try and be constructive, and positive, when we do so (and, similarly, responding positively when people provide constructive criticism).

I really don’t have any suggestions as to how to deal with the harassment that some experience, but maybe we do need to try and remember how isolating social media can be and try to be more supportive of those who are engaging publicly. It won’t somehow negate the appalling harassment that some experience, but at least it shouldn’t make it worse. I know it’s not enough, and maybe it’s not even really a start, but it’s all that I can think of and it’s all that I think I can do. Maybe others, however, have better suggestions.

Posted in Climate change, ClimateBall | Tagged , , , , , , | 96 Comments

Lukewarmers resurgent

I’ve noticed a slight resurgence in those claiming to be lukewarmers and trying to argue that this is some kind of reasonable middle ground. I’ve written about lukewarmers before, but the basic issue with the lukewarmer argument is that they take something that is possible (low climate sensitivity) and argue that it is almost certain. The problem, quite obviously, is that arguing that something is likely, when it’s not, is not consistent with the available scientific evidence.

I think, however, that focusing on something like climate sensitivity somewhat misses a key point (intentionally possibly). The chance that climate sensitivity could be so low that we can continue to pump CO2 into the atmosphere, without any chance of the resulting changes leading to potentially damaging impacts, is almost certainly very small. Even if climate sensitivity is on the low side of the range, we can still pump enough CO2 into the atmosphere for the changes to be large and for the resulting impacts to be severe.

What I’m suggesting is that even lukewarmers (assuming that they would like to avoid changes that could have damaging impacts) should be willing to consider how we should be aiming to reduce our emissions. We can debate how best to go about reducing emissions, and how fast we should be aiming to do so, but the idea that we don’t need to do so is – I would argue – not even consistent with a reasonable lukewarmer position. Well, unless – as some suspect – lukewarmers are really just selecting their scientific position to suit their policy preferences.

I don’t know if I’ve expressed this as clearly as I might have, but what I’m really trying to suggest is that from a global warming perspective, the key factor (at least, the one over which we have some control) is our emissions. Is there a realistic scenario under which we can continue to pump CO2 into the atmosphere without producing impacts that are severely damaging? I would argue that the answer is no, even if you think that climate sensivity might be on the low side of the range.

Posted in Climate change, Climate sensitivity, Global warming, Greenhouse effect, Politics, Science | Tagged , , , , | 657 Comments

The crisis of free speech in higher education

I came across an interesting post by Mark Carrigan called the (coming) crisis of free speech in the digital university. The underlying issue is the suggestion that there is a crisis of free speech in higher education. This is related, I think, to the lack of viewpoint diversity, highlighted by the Heterodox Academy, who seem to think that we should be actively aiming to increase viewpoint diversity because

[f]ree speech and the exploration of unsettling ideas is threatened on many campuses.

I’ve written about the Heterodox Academy before and have been mostly unimpressed by what they suggest. If you want to know why, you should really read the earlier posts, but it’s not because I don’t think we should have more viewpoint diversity. My main concerns are that if biases are influencing how research is undertaken then we should improve scholarship, not introduce new biases. Additionally, I don’t actually see how we can actively increase viewpoint diversity, at least not in a way that doesn’t ultimately suppress other viewpoints.

As Mark Carrigan’s post says

The crisis of free speech in higher education is overdetermined. ….

…. we urgently need to reject the idea that the crisis of free speech is a matter of censorious millennials undermining the institutional culture of the university. This is such obvious nonsense as an account of the change underway in our universities that it wouldn’t even be worth engaging with, if it were not promulgated with such vigour by so many influential outlets.

There clearly are things happening on campus that all who value free speech should condemn. There are indications that the institutions themselves are trying to discourage speaking freely, there are some cases where the state itself appears to be suppressing certain views, and there are also even some activities on campuses that are objectionable.

However, many of those who are arguing that there is a crisis of free speech in higher education seem to use isolated events to suggest that the problem is pervasive; that the academy is full of people who are trying to suppress alternative views. The problem with this is that isolated extreme events can then be used to delegitimise any criticism of alternative views, which – ultimately – then acts to suppress the criticism.

I’ve seen similar tactics in the climate debate. Many who are regularly criticised will use extreme cases to suggest that all their critics behave in this way and, hence, that their critics are not only behaving in an unreasonable manner, but can be ignored.

This is my problem with the claims of a crisis of free speech in the academy. I don’t think that it is motivated by a genuine desire to protect free speech, but by a desire to promote certain views that are not as prominent as they would like. Rather than simply finding stronger arguments, they’re attempting to suggest that the academy is full of people who are trying to actively suppress alternative views, rather than there simply being many people who happen to disagree with their views.

I think there are valid free speech issues in higher education, but I really don’t think that the problem is that higher education is dominated by people who want to suppress alternative views. It may well be that some views dominate over others, but that’s probably inevitable; if those who hold under-represented views want these views to be more prominent, they should make more convincing arguments, not try to suppress those who do not agree with them.

Posted in Freedom Fighters, Politics, The philosophy of science, Universities | Tagged , , , , | 132 Comments

Trump and Paris

So, Trump has decided to withdraw from the Paris climate accord. It’s not really a great surprise, but disappointing nonetheless. The thing that gets me is how inconsistent the arguments for leaving seem to be. I particularly liked David Roberts’s article which pointed out that the Paris climate deal can’t be both nonbinding and draconian. Similarly, people seem to justify leaving on the basis of the Paris accord not really achieving much. Well, it wasn’t intended to be the final step and if it isn’t achieving enough, surely the solution is then to do more, not less.

However, some of the claims of it achieving little are wrong. It’s suggested that it would only reduce global temperatures by a few tenths of a degree by 2100. However, this is only likely if, after 2030, we simply give up, and go back to increasing our emissions. As illustrated by the figure on the right, [f]ull implementation of current Paris pledges plus all announced mid-century strategies would reduce expected warming by 2100 to 3.3°C, a difference of 0.9°C.

However, I actually think the momentum is going to be diffiult to stop. Lots of countries are starting to think of ways to reduce theirs emissions, and even many US states have claimed that this will not influence their intention to reduce emissions. So, when it comes to addressing climate change, the US withdrawing from the Paris accord may not be that significant. It may mean that we don’t reduce emissions as fast as we might have otherwise done, but I suspect that the overall effect will be small.

What I think is more concerning are the geopolitical implications of this decision. A global superpower has decided to withdraw from an agreement that was aimed at addressing what might be the most important global issue of this age; essentially the US will no longer be playing a leadership role. Other countries will be, and already are, stepping in to take on this leadership role and the influence of the US in the world will be diminished. Not only that, there are economic implications. It seems clear that we will be seeing more and more of a shift away from fossil fuels, and those who embrace this will probably benefit more than those who do not.

I don’t have a good sense of the implications of the above. Maybe there aren’t many. However, it would certainly seem better to have the US playing a leading role, than taking a step back and allowing others to take over this leadership role. I don’t think it’s going to be easy to take it on again, and I hope they don’t regret allowing this to happen.

Posted in Climate change, Global warming, Politics | Tagged , , , , | 179 Comments