Archive for April, 2010

Give Credit Where It’s Due Man!

April 26, 2010

I seem to recall I mentioned previously a paper by Petr Chylek and colleagues about the “Atlantic Multidecadal Oscillation” and polar temperature changes-I just checked, I didn’t mention it before. Well, thanks to Roger Pielke Sr’s blog, I have recently learned about a new, similar paper the same group has written about both poles. Now, I pretty much agree with Roger’s statements about what is good about the paper and what is not-I think their comments about the “general warming” are unfounded though not implausible. But I do have to take issue with this:

A bi‐polar seesaw pattern of the paleo temperature has been observed earlier in the Greenland and Antarctic ice core data. For the first time we identify a bi‐polar seesaw pattern in the 20th century Arctic and Antarctic instrumental temperature records.

I take issue with this group claiming they are the first to point out that the behavior of the Arctic and Antarctic are out of phase on this timescale. Indeed, this has been pointed out in the context of the “cosmic ray hypothesis” (see figure 6) by Henrik Svensmark-whether you believe it is due to his suggested idea or not, cloud albedo is a plausible mechanism. So why would anyone claim they thought of this first? Maybe they just were unaware of it?

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The Incredible Undrying Wilderness

April 20, 2010

Wasn’t that the title of a classic novel or something? Anyway, In our continuing quest to test claims of climate impacts, some have pointed out to me in discussions that while there may not be strong evidence for certain kinds of impacts in some places, some of the claims are (sometimes, depending on whose claims) dependent on geography. Sure, the US isn’t drying up catastrophically (you know, where we grow enough food for some huge percentage of the world’s population)-but what about the rainforest (or something else)!

If I were my father’s age, I’d be tempted to say “We still have that?”-Well, I’m not. And we already commented on the global drought changes. But with regard to the Amazon in particular, once again WCR has drawn my attention to an interesting article, about precipitation there. It seems that, since 1920, there are no signs of significant decreases in precipitation (although there are insignificant declines in the North) and some statistically significant increases in precipitation in Southern Amazonia. Despite the drying influence of deforestation and (allegedly) AGW, the multidecadal variability and long term trends show the Amazon is NOT drying up. If this has been the case during the warming of the last century, it is hard to see how a radically difference response to future warming could occur.

A side note on precipitation: I highly recommend this excellent post by Willis Eschenbach which does something I’ve wanted to do for a while: show the spatial variations in US precipitation trends. He also analyzes the Palmer Drought Severity Index, which we’ve mentioned before.

No Increase In Category 4 and 5 Tropical Cyclones In The Northern Hemisphere Since 1987

April 8, 2010

NOTE: Golly, this is embarrassing, in my sloppiness, I seem to have forgotten about the Northern Indian ocean. Unfortunately the North Indian does not seem to have completely reliable data over the period in question (apparently before 1990 they only reported twelve hourlies instead of six) NEVERTHELESS you shall see that this update doesn’t change anything about the conclusions. This suggests that the lack of increase in 4’s and 5’s is “robust” in the Team sense.

One of the common claims made about global warming is that there will be an increase in the frequency of the strongest tropical cyclones in a warmer world, and this is already evident[1, 2]. These claims have been criticized on the grounds that early observational data is not as accurate as present data[3] and ignoring decadal variability[4, 5]. Homogeneous satellite data fail to corroborate the large claimed trend, although they may indicate some intensity increase over the short period (note that they are thus still problematic due to decadal  variability)[6, 7]. A previous look at data since 1986[8] did identify a small increase in the number of category 4 and 5 storms in the North Hemisphere, and a larger but more suspect trend in the Southern Hemisphere. Theoretically speaking, one might expect, all other things being equal, that hurricanes would become slightly more intense over warmer sea surface temperatures[9], in order for this to play out in the real world, the factors other than sea surface temperature must not counteract this tendency, which has not been shown-indeed, the “Maximum Potential Intensity” is not well correlated with TC activity except in the North Atlantic[10] and it appears that while local warming may enhance activity, it does so only if it occurs more so than the tropical mean[11, 12] since widespread warming tends to increase “outflow” temperatures that act against increasing MPI. It is also worth pointing out that trends which have significance for society must pan out in terms of landfalling statistics, which have been under examined in terms of intensity. So even the small increases now claimed, if really due to sea surface warming, which has not been demonstrated, may have no significance for society, and if they do, because they are not large trends their importance may not manifest in terms of actually additional damages for some time, if at all.

Here, I will examine the issue of increases in the number-but not the proportion-of “intense” storms (category four and five on the Saffir Simpson Scale). Since 1987, the Western North Pacific basin has been entirely reliant on satellite monitoring due to discontinuing the Aircraft reconnaissance period, and satellite monitoring of the Atlantic and Eastern Pacific basin appears to have been adequate and fairly similar throughout this period. The Northern Indian appears problematic in the earliest years, but is nevertheless included as it does not appear to effect the results either way. In the North Hemisphere, there has been plenty of tropical warming over this period, so if there were an increase in storm intensity as a consequence in should be obvious. The presence of such a trend would not prove causation by warming (because of the decadal variability issue), but the absence of such a trend or a decrease would speak volumes about the validity of that hypothesis. Although this period is shorter than examined by the Elsner et al study[7] again if that studies trend is actually related to steadily rising sea surface temperatures, it shouldn’t be confined entirely to 1981-86.

Figure one shows the number of category four and five tropical cyclones in the Eastern North Pacific, Western North Pacific, Northern Indian, and North Atlantic basins summed together over the 1987-2009 period according to “best track” data[13] and Joint Typhoon Warning Center/HURDAT intensities, and an OLS fit line. As can be seen there is a slight decrease over this period despite significant warming, although the downward trend is obviously so small as to be insignificant.

Fig 1-Category 4 and 5 Tropical Cyclones in the North Atlantic, Western North Pacific, Northern Indian, and Eastern North Pacific from 1987 to 2009, with linear trend

The reason for the lack of increase in the Northern Hemisphere is primarily that the Eastern Pacific has seen a decline in these intense cyclone frequencies. The reasons for this tendency need to be better understood before attempting to attribute increases elsewhere to warming, since it appears that whatever has caused a decrease there must be some natural phenomenon which probably plays a role in the other basins. Indeed, it has been observed that overall activity in the ENP and NATL basins behave in complementary ways[14]-when one is active, the other is inactive, and vice versa.

None of this is contradictory to the recent “consensus” statement by the research community[15] that “it remains uncertain whether past changes in tropical cyclone activity have exceeded the variability expected from natural causes.”

With regard to the longer term, further study must be done to try and get homogeneous datasets as far back as possible, and the causes of decadal variability better understood.

[1]Webster, P. J., G. J. Holland, J. A. Curry, and H.-R. Chang (2005), Changes in tropical cyclone number and intensity in a warming environment, Science, 309, 1844–1846.

[2]Emanuel, K. A. (2005), Increasing destructiveness of tropical cyclones over the past 30 years, Nature, 326, 686– 688.

[3]Landsea, C.W., B.A. Harper, K. Hoarau, J.A. Knaff. 2006. Can We Detect Trends in Extreme Tropical Cyclones? Science, 313, 452-454.

[4]Chan, J. C. L., 2008: Decadal variations of intense typhoon occurrence in the western North Pacific. Proc. R. Soc. A, 464, 249−272.

[5]Goldenberg, S. B., C. W. Landsea, A. M. Mestas-Nuñez, and W. M. Gray (2001), The recent increase in Atlantic hurricane activity: Causes and implications, Science, 293, 474– 479.

[6]Kossin, J. P., Knapp, K. R., Vimont, D. J., Murnane, R. J. & Harper, B. A. A globally consistent reanalysis of hurricane variability and trends. Geophys. Res. Lett. 34, L04815 (2007).

[7]Elsner, J. B., Kossin, J. P. & Jagger, T. H. The increasing intensity of the strongest tropical cyclones. Nature 455, 92–95 (2008).

[8]Klotzbach, P.J., 2006. Trends in global tropical cyclone activity over the past twenty years (1986-2005). Geophysical Research Letters, 33, L010805, doi:10.1029/2006GL025881.

[9]Emanuel, K. A. The dependence of hurricane intensity on climate. Nature 326, 483–485 (1987).

[10]Chan, J.C.L. 2009. Thermodynamic control on the climate of intense tropical cyclones. Proceedings of the Royal Society A, 465, 3011-3021.

[11]Swanson, K.L, 2007. Impact of scaling behavior on tropical cyclone intensities. Geophysical Research Letters, 34, doi:10.1029/2007GL030851.

[12]Vecchi, G.A. and B.J. Soden. 2007. Effect of remote sea surface temperature change on tropical cyclone potential intensity. Nature, 450, 1066-1071.

[13]Knapp, K. R., M. C. Kruk, D. H. Levinson, H. J. Diamond, and C. J. Neumann, 2010: The International Best Track Archive for Climate Stewardship (IBTrACS): Unifying tropical cyclone best track data. Bulletin of the American Meteor. Society, In press.

[14]Maue, R. N. (2009), Northern Hemisphere tropical cyclone activity, Geophys. Res. Lett., 36, L05805, doi:10.1029/2008GL035946.

[15]Knutson, T. R. et al (2010), Tropical cyclones and climate change, Nature Geoscience 3, 157 – 163, doi:10.1038/ngeo779

Some Random Results

April 4, 2010

Seeing as this is a blog about testing hypotheses, I thought that I’d like to discuss a somewhat esoteric problem in doing such tests-namely, how to characterize one’s expectations or “null” hypotheses. The problem may be conceptually thought of this way: Suppose I want to test whether there is a “trend” in data which is sufficiently large that you can place high confidence that it is actually there and not just a fluctuation due to random chance. The problem is how to characterize the probability distribution function of trends due to chance. The simplest kind of assumption is the distribution that would arise out of pure “white noise”-basically every data point in a time series which is white noise will have no dependence on the points before (or after) them, although this is hardly the only thing that white noise is usually characterized by. The thing about white noise is that it is not going to tend to display “trends” very often. When you use white noise as your null hypothesis, rather than asking “how likely is it that this trend arose by chance” you are really asking, “how likely is it that this trend could occur from white noise”. Now, if the random behavior in the system you are looking at is a priori expected to behave like white noise, this is not wrong. But if you really expect the system to behave in a manner which is not like white noise, you are using a null hypothesis which will end up being too easy to reject.

For instance, by generating random (white noise) numbers and giving them the same mean and standard deviation that is found in NCDC’s US national annual precipitation, I estimate that the apparent trend in US precipitation is very nearly three standard deviations from the expected mean of my white noise base trend distribution. In other words the trend that appears to have taken place is highly significantly different from zero assuming that precipitation variability acts like white noise. But is it really the case that the probability of the trend in US precipitation occurring by chance is on the order of .1%? I doubt it. In reality the precipitation data has a correlation with itself of r~0.210 versus the simulated r of ~-0.002. In other words, there is some (albeit very little) dependence of data points in the actual precipitation record on precipitation in the previous year. The white noise synthetic data has no auto-correlation whatsoever (of course) and indeed the very weak r is actually negative(!). This implies that our synthetic data has a slightly lower tendency to exhibit trend behavior than reality. So, really, I don’t think the actual significance of the US precipitation trend is really three sigma.

Lock Out

April 1, 2010

In previously, I have talked about the incredible process that Ross McKitrick went through trying to get papers published showing that the land surface temperature data is exaggerating warming due to biases from non climatic factors. In this document from March 25th, Ross describes in great detail his related effort to rebut the IPCC’s bizarre claim that they could discount his findings on the basis of-well, actually they had no real basis, but claimed that the Arctic Oscillation etc. explained this(!) somehow. It turns out that journal after journal used lame, contradictory, and false excuses for rejecting the paper, and multiple journals just started ignoring his attempts to appeal these decisions. What appears to be going on is a full-on lock-out from the peer reviewed climate literature-disagree with the IPCC on this issue, you’ll find that something odd seems to occur-nobody will publish your work. Ever. So you’ll have to publish in stats journal or something. And the gatekeepers will still dismiss your work on totally illegitimate, fabricated grounds.

What else is new.