Archive for the ‘Risk & Uncertainty’ Category

Visually Pleasing Temperature Adjustments

June 2nd, 2008

Posted by: Roger Pielke, Jr.

This is a follow up to our continuing discussion of the possible implications of changes to mid-century global average temperatures for conclusions reached by the IPCC AR4, and how scientists react to such changes.

Over at Real Climate they pointed to the following figure as representing “a good first guess at what the change will look like” and asserted that it would have no meaningful implications for the trends in temperature rise since mid-century presented by the IPCC.

independent graph.jpg

Since there was some disagreement here in the comments of an earlier post about how to interpret this graph, I have decided to simply replicate it and then see if I could exactly replicate the graph from the Independent. The data is available here.

The first thing to note is that the Independent graph has a major error which Real Climate did not point out. It says that the smooth curve represents a 5-year average, when in fact, it actually represents a 21-point binomial filter. The difference in smoothing is critically important for interpreting what the graph actually says, and the error confused me and at least one climate scientist writing in our comments.

Here is a replication of the 21-point smoothing generated from the annual values, which will allow for my effort to replicate the graph from the Independent.

smooth seas.jpg

So far so good. But replication of the adjusted curve is a bit tricky as changing data for any one year has implications for the shape of the curve 10 years before that year and 10 years after. Upon trying to create a exact replication of the graph from The Independent, right away I realized that there was a major problem, because adding any increment to where Thompson et al. said it should begin (in 1945) instantly raised the adjusted curve to a point above the unadjusted curve. And as you can see in the Independent graph that at no point does the adjusted curve rise above the unadjusted curve, much less by a significant amount as implied by Thompson et al..

So right away it seems clear that we are not trying to make an adjustment that actually draws on the guidance from Thompson et al. This might seem odd, since the graph is supposed to show a proposed “guess” at the implications of Thompson et al. In any event, with that constraint removed I simply tried to get the best visual fit to the Independent graph that I could. And here is what I came up with.


Now, given the complicated smoothing routine, there is certainly any number of combinations of weird adjustments that will result in a very similar looking curve. (And if anyone from CRU is reading and wants to share with us exactly what you used, and the basis for it, please do so.) The adjustments I used are as follows:

1945 0
1946 0
1947 0
1948 0.1
1949 0.25
1950 0.18
1951 0.18
1952 0.18
1953 0.18
1954 0.16
1955 0.16
1956 0
1957 0
1958 0
1959 0
1960 0

Oh yeah, the effect of these visually pleasing adjustments on the IPCC trend from 1950? Not that it actually means anything given the obvious incorrectness, but it would reduce the trend by about 15%.

The Helpful Undergraduate: Another Response to James Annan

May 16th, 2008

Posted by: Roger Pielke, Jr.

In his latest essay on my stupidity, climate modeler James Annan made the helpful suggestion that I consult a “a numerate undergraduate to explain it to [me].” So I looked outside my office, where things are quiet out on the quad this time of year, but as luck would have it, I did find a young lady named Megan, who just happened to be majoring in mathematics who agreed to help me overcome my considerable ignorance.


How to Make Two Decades of Cooling Consistent with Warming

May 12th, 2008

Posted by: Roger Pielke, Jr.

The folks at Real Climate have produced a very interesting analysis that provides some useful information for the task of framing a falsification exercise on IPCC predictions of global surface temperature changes. The exercise also provides some insight into how this branch of the climate science community defines the concept of consistency between models and observations, and why it is that every observation seems to be, in their eyes, “consistent with” model predictions. This post explains why Real Climate is wrong in their conclusions on falsification and the why it is that two decades of cooling can be defined as “consistent with” predictions of warming.


Real Climate’s Bold Bet

May 9th, 2008

Posted by: Roger Pielke, Jr.

The Real Climate guys have offered odds on future temperature changes, which is great because it gives us a sense of their confidence in predictions of future global average temperatures. Unfortunately, RCs foray into laying odds is not as useful as it might be.

The motivation for this bet is the recent Keenlyside et al. paper that has caused a set of mixed reactions among the commenters in the blogosphere. Some commenters here have stridently argued that the predictions in the Keelyside et al. paper are perfectly consistent with predictions of climate models in the IPCC. However, when one such commenter here was asked to show a single IPCC climate model run showing no temperature increase for the 2 decades following the late 1990s he submitted an irrelevant link and disappeared. Others have argued that the Keenlyside et al. projections (and this includes Keenlyside) are inconsistent with the IPCC predictions. Real Climate apparently falls into this latter camp.

The Real Climate Bet (and there is also one for a later period) is that the period 1994-2004 will have a higher average temperature than the period 2000-2010. Since the periods have in common 2000-2004, we can throw those out as irrelevant. Thus, the bet is really about whether the period 1994-1998 will be warmer than the period 2005-2010. And since we know the temperatures for 2005 to present, the bet is really about what will happen in 2009 and 2010. (Using UKMET temps here.)

It is strange to see the Real Climate guys wagering on 2-year climate trends when they already taught us a lesson that 8 years is far to short for trends to be meaningful. But perhaps there is some other reason why they offer this bet. That reason is that they are playing with a stacked deck, which is what you do when looking for suckers. The following figure shows why.


For the Real Climate guys to lose the bet global average temperatures for 2009 and 2010 would have to fall by about 0.30 from the period 2005-present (and I’ve assumed Jan-Mar as the 2008 value, 2008 obviously could wind up higher or lower). Real Climate has boldly offered 50-50 odds that this will happen. This is a bit like giving 50-50 odds that Wigan will come back from a 3-0 halftime deficit to Manchester United. Who would take that bet?

Another interpretation of the odds provided by RC is that they actually believe that there is a 50% chance that global temperatures will decrease by more than 0.30 over the next few years. Since I don’t think they actually believe that, it is safe to conclude that they’ve offered a suckers bet. Too bad. When Real Climate wants to offer a 50-50 bet in which the bettor gets to pick which side to take in the bet (i.e., the definition of 50-50) then we’ll know that they are serious.

Teats on a Bull

May 8th, 2008

Posted by: Roger Pielke, Jr.

Here is a very thoughtful comment sent in by email on the ““consistent with chronicles”. I haven’t identified the author, since he didn’t ask me to post it. But it is worth a read about how climate science is received by one rancher in West Tennessee. I appreciate the feedback.


Kudos to Kerry Emanuel

April 11th, 2008

Posted by: Roger Pielke, Jr.

I have always held Kerry Emanuel in high regard, because he calls things like he sees them, but he also listens to others who might not share his views. He is, in short, a great scientist.

So it was not too surprising to see that Kerry’s views have evolved on the issue of hurricanes and climate change, as science has progressed. A Houston Chronicle story reports today the following:

One of the most influential scientists behind the theory that global warming has intensified recent hurricane activity says he will reconsider his stand.

The hurricane expert, Kerry Emanuel of the Massachusetts Institute of Technology, this week unveiled a novel technique for predicting hurricane activity. The new work suggests that, even in a dramatically warming world, hurricane frequency and intensity may not substantially rise during the next two centuries.

The research, appearing in the March issue of Bulletin of the American Meteorological Society, is all the more remarkable coming from Emanuel, a highly visible leader in his field and long an ardent proponent of a link between global warming and much stronger hurricanes.

His changing views could influence other scientists.

“The results surprised me,” Emanuel said of his work, adding that global warming may still play a role in raising the intensity of hurricanes but what that role is remains far from certain.

I emailed Kerry to ask if the story accurately reflected his views. He replied that it was a bit exaggerated, but basically OK. Those engaged in the political debate over climate change who are skeptical of a link between hurricanes and climate change might try to make some hay from this news report. But here at Prometheus we’d suggest viewing Kerry’s evolving view in the much broader context, which we have shared on multiple occasions, namely:

there are good reasons to expect that any conclusive connection between global warming and hurricanes or their impacts will not be made in the near term.

So don’t get to excited about the latest paper in hurricane climatology, the field evolves slowly, and the views of of our best scientists evolve with it.

Green Car Congress on PWG

April 8th, 2008

Posted by: Roger Pielke, Jr.

Here is a link to an excellent summary and thoughtful discussion of our Nature Commentary (PWG) at Green Car Congress written by Jack Rosebro.

Commentary in Nature

April 2nd, 2008

Posted by: Roger Pielke, Jr.

[Update #4: The guys at Grist Magazine apparently have not yet read our paper, which probably explains why one of their commentators explains that everything we say is right but common wisdom, while another says that everything we say is wrong. At least they have their bases covered. Why don't these guys at Grist actually read the paper before commenting? One wonders.]

[Update #3: Andy Revkin of the NYT provides some comments as well here.]

[Update #2: John Tierney of the NYT times provides excerpts of an extended set of comments that I shared with him here.]

[Update: Here is a short interview I did with Scitizen link.]

Tom Wigley, Chris Green, and I have a Commentary in today’s Nature on the technology challenge of stabilization. It has already generated some discussion and this discussion will be the focus of some of my posts over the next weeks.

Meantime, please have a look at this summary that Tom, Chris, and I prepared:


LA Times on Adaptation

March 26th, 2008

Posted by: Roger Pielke, Jr.

Pielke LA Times.gif

The image above is from a LA Times story by Alan Zarembo and is based on some of our reserach on future hurricane damages under changes in both climate and society. Zarembo provides a perspective on a group of scholars and advocates that I once called “nonskeptical heretics.” Nonskeptical because they accept the science presented by the IPCC (as noted by Zarembo), and heretics because they take strong issue with many of the closely held assumptions that have come to frame the debate over climate policies.

Zarembo characterizes one of the most insidious assumptions — that support for adaptation necessarily means a loss of support for mitigation:

Other scientists say that time is running out to control carbon dioxide emissions and that the call to adapt is providing a potentially dangerous excuse to delay. . . Although most scientists agree that adaptation should play a major role in absorbing the effects of climate change, they say that buying into the heretics’ arguments will dig the world into a deeper hole by putting off greenhouse gas reductions until it is too late.

Well, no. It is a strawman to argue that strong support for adaptation means that one cannot also provide strong support for mitigation. A problem arises for mitigation-first proponents when they invoke things like hurricanes, malaria, and drought as justification for mitigation when clearly adaptive responses will be far more effective. Those who persist in linking mitigation to reducing such climate impacts will always find themselves on the wrong side of what research has shown — namely, climate change is a much smaller factor in such impacts than societal factors (compare the graph above). It is true. Get over it.

The best arguments for mitigation were presented by Zarembo coming from Steve Schneider, who rightly pointed to the uncertain but highly consequential impacts of human-caused climate change:

“You can’t adapt to melting the Greenland ice sheet,” said Stephen H. Schneider, a climatologist at Stanford University. “You can’t adapt to species that have gone extinct.”

If advocacy for action on mitigation emphasized these very large scale long-term impacts, rather than disasters, disease, etc., then there would be no need for adaptation and mitigation to be presented as opposing approaches. Consider that none of the people quoted in the Zarembo story who I know (including me) have suggested that adaptation can replace mitigation, particularly for issues like sea level rise and specifies extinction. So the argument that adaptation can’t deal with sea level rise over a century or more is somewhat of a strawman as well.

The reality is that whatever the world decides to do on mitigation, we will have no choice but to improve our adaptation to climate. Humans have been improving their adaptation to climate forever and will continue to do so. Since we are going to adapt, we should do it wisely. And this means rejecting bad policy arguments when offered in the way of substitutes for adaptation, like the tired old view that today’s disaster losses are somehow a justification for changes to energy policies. Misleading policy arguments and should be pointed out as such, because they hurt both the cause of adaptation, but ironically the cause of mitigation as well.

If mitigation advocates do not like being told that their misleading arguments poorly serve policy debate, well, they should probably try to come up with a more robust set of arguments. Arguing that support for adaptation undercuts support for mitigation is a little like making the argument that support for eating healthy and getting exercise (adapting one’s lifestyle) undercuts support for heart surgery research (mitigating the effects of heart disease). Obviously we should seek both adaptation and mitigation in the context of heart disease.

If the case for action on energy policy is so overwhelmingly strong (and again, I think that it is), then there should be no reason to resort to misleading arguments completely detached from the conclusions of a wide range of analyses. Misleading arguments may be politically expedient in the short term, but cannot help the mitigation cause in the long run. And dealing with the emissions of greenhouse gases will take place over the long run. Meantime, we’ll adapt.

Update on Falsifiability of Climate Predictions

March 15th, 2008

Posted by: Roger Pielke, Jr.


UPDATE 2:40PM 3-15-08: Within a few hours of this post, as we might have expected, rather than contributing to the substantive discussion, a climate scientist chooses instead to tell us how stupid we are for even discussing such subjects. We are told that “until the temperature obviously and unambiguously turns up again, this kind of stuff is going to continue.” Isn’t that what this post says? For the “stuff” read on below.

Regular readers will recall that not long ago I asked the climate community research community to suggest what climate observations might be observed on decadal time scales that might be inconsistent with predictions from models. While Real Climate has decided to take a pass on this question other scientists and interested observers have taken up the challenge, no doubt with interest added by the recent cooling in the primary datasets of global temperature.

A very interesting perspective is provided by Lucia Liljegren, who has several interesting posts on observations versus predictions. The figure above is from her analysis. Her complete analysis can be found here. She has several follow up posts in which she discusses other aspects of the analysis and links to a few other, similar explorations of this issue. She writes:

No matter which major temperature measuring group we examine, or which reasonable criteria for limiting our choices we select, it appears that possible that something not anticipated by the IPCC WG1 happened soon after they published their predictions for this century. That something may be the shift in the Pacific Decadal Oscillation; it may be something else. Statistics cannot tell us.

It may turn out that this something is a relatively infrequent but climatologically important, feature that results in unusually cold weather . Events that happen at a rate of 1% do happen– at a rate of 1%. So, if recent flat trend is the 1% event, then 30 year trend in temperatures will resume.

For what it’s worth: I believe AGW is real, based on physical arguments and longer term trends, I suspect we will discover that GCM’s are currently unable to predict shifts in the PDO. The result is the uncertainty intervals on IPCC projections for the short term trend were much too small.

Of course, the reason for the poor short term predictions may turn out to be something else entirely. It remains to those who make these predictions to try to identify what, if anything, resulted in this mismatch between projections and short term data. Or to stand steadfast and wait for La Nina to break and the weather to begin to warm.

Those wanting to quibble with her analysis would no doubt observe that the uncertainty around IPCC predictions for the short term is undoubtedly larger that then IPCC itself presented. Lucia in fact suggests this in her analysis, making one wonder if uncertainties are indeed larger than presented, why didn’t the IPCC say so?

In 2006 my father and I wrote about the possible effects on the climate debate of short-term predictions that do not square with observations:

predictions represent a huge gamble with public and policymaker opinion. If more-or-less steady global warming does not occur as forecast by these models, not only will professional reputations be at risk, but the need to reduce threats to the wide spectrum of serious and legitimate environmental concerns (including the human release of greenhouse gases) will be questioned by some as having been oversold. For better or worse, a failure to accurately predict the changes in the global average surface temperature, global average tropospheric temperature, ocean average heat content change, or Arctic sea ice coverage would raise questions on the reliance of global climate models for accurate prediction on multi-decadal time scales.

In one of the comments in response to that post a climate scientist (and Real Climate blogger) took us to task for raising the issue suggesting that there was no really reason to speculate about such things given that, “I’ve pointed out that in the obs, there is no sign of > 2 yr decreasing trends.”

Another climate scientist commented that climate models were completely on target:

Re the possibility that the Earth is acting in a way that the models hadn’t predicted, I must say I’m pretty relaxed about that. Let’s wait a few more years and see, eh?

I have not yet seen rebuttals to Lucia’s analysis, or others like it (she points to a few), which are not peer-reviewed analyses, yet certainly of some merit and worth considering. There continues to be good reasons for climate scientists to begin more openly discussing the limitations of short-term climate predictions and the implications for understanding uncertainties. They have these discussions among themselves all of the time. For example, with a view quite similar to my own, Real Climate’s Gavin Schimdt suggests that if the full context of a prediction from a climate model is not understood, then:

model results have an aura of exactitude that can be misleading. Reporting those results without the appropriate caveats can then provoke a backlash from those who know better, lending the whole field an aura of unreliability.

None of this discussion means that the basic conclusion that greenhouse gases affect the climate system is wrong, or that action to mitigate emissions do not make sense. What it does mean is that we should be concerned about the overselling of climate predictions and the corresponding risks to public credibility and advocacy built upon these predictions.