Climate Etc.

JC interview: hurricanes and global warming

by Judith Curry

My recent interview with David Whitehouse of the Global Warming Policy Foundation on Hurricanes Harvey and Irma and the link with global warming.

The video of the interview:

Transcript:

DW:  First of all – do we understand hurricanes?

JC:  We’re getting a whole lot better at predicting individual storms. This has really been a banner year for long range prediction, and detailed prediction for hurricane impacts. Models like ECMWF {European Centre for Medium-Range Weather Forecasts} and the NOAA models – they’re doing a good job. We understand the basics of how hurricanes form and we have a predicative capability using high resolution global and regional weather forecast models. We don’t understand rapid intensification. Like hurricane Harvey this year – it spun up very quickly, rapidly intensified, in less than 24 hours. We don’t know how to predict that much in advance. But in terms of track and overall intensity, rainfall impacts, we’re getting pretty good at being able to predict that. My company Climate Forecast Applications Network (CFAN) — hurricane forecasting is a big part of what we do, and we’ve have a really good year for our predictions.

DW: What do we know about, looking backward, in the past, what do we know about the rate of change of the intensity of hurricanes, or the frequency of occurrence.

JC:  We only have good satellite data back to maybe 1980. We have some satellite date going back to 1970. But it is of lesser quality. We don’t have long global records. But in the Atlantic, we have pretty good historical records, at least for the landfalling hurricanes. But not necessarily for the total number in the ocean basins. For the satellite record globally, there’s no trend in the numbers or overall accumulated cyclone energy. We have teased out a signal, of increasing percentage of category four and five hurricanes in two of the basins in the Atlantic and the North Indian Ocean. But trying to determine whether this is natural variability or human-caused — we just don’t have a long enough record to tease that out. There are hints of an increasing percentage of category four and five hurricanes, but we don’t have the knowledge or enough data to attribute that to humans versus natural variability.

DW: But some people have said that as a result of hurricane Harvey and Irma, that we live in a warmer world, the oceans are warmer, the sea level is higher, and this is going to make hurricanes more destructive. What do you think of that?

JC: Can they then tell me why we’ve had no major hurricanes strikes in the US for the twelve years preceding Hurricane Harvey? Sea surface temperature is only one ingredient for hurricane development and intensification, and it doesn’t seem to be absolute sea surface temperature, either. You can go back and there were really strong hurricanes in the nineteenth century for example, where surface temperatures were significantly cooler. And there were some horrendous hurricanes in the Atlantic in the early part of the twentieth century, when sea surface temperatures were noticeably cooler. It’s more relative sea surface temperatures and the overall dynamics of the atmosphere that are arguably the key ingredients – not just absolute sea surface temperature itself.

We now have a pretty good predictive capability of individual hurricanes. Our understanding of the climate dynamics of hurricanes is a different story. This is something that’s still a work in progress. There is a lot of debate in the scientific community about this, and we’re only now starting to see some high resolution global climate model simulations trying to sort out what we might see in the future.

There was a paper just published by a Japanese group: “Response of Tropical Cyclone Activity and Structure to Global Warming in a High-Resolution Global Nonhydrostatic Model” by Yohei Yamada et al. in the Journal of Climate. They ran the very high resolution Japanese climate model for the current conditions of perturbed warmer conditions, and they found a significant decrease in the number of hurricanes, but they found an increase in intensity, an increase in the horizontal size, which relates to storm surge among other things, and an increase in precipitation. I just glanced at it literally yesterday – I flagged it to read more carefully. But that may be the best study that I’ve seen of that kind. For the sake of argument, assume that is correct. What is the trade-off for 20% fewer hurricanes for a slight increase in overall intensity. In terms of overall damage. I don’t know what the trade-off is, so it might not be a net increase in actual damage if there’s fewer hurricanes. That’s the state of our understanding right now.

DW:  So, given the models — what the models say — What people might say will happen in the future, how long will it be before we are observationally able to compare what’s happening with the models?

JC: Kerry Emanuel has said that it will be mid-twenty-first century before we’d expect to see any climatological signal in the observations, because natural variability is so large. And weather roulette — sometimes crazy things happen, and then they don’t have anything to do with climate. By the time you have a long enough time — and this is assuming that we have some substantial warming over the next thirty years — if we do have substantial warming over the next thirty years, probably by 2050 we would start to be able to tease out a signal.

But looking at that period, the next 30 years, we’re probably looking at a shift in the Atlantic to the cool phase of the Atlantic multidecadal oscillation. In 1995, after a relatively quiet period in the Atlantic, we flipped to the warm phase of the Atlantic multidecadal oscillation, and that like really juiced-up the hurricanes. And so, at some time, probably in the order of ten years, we’ll see a flip to the cool phase again, and presumably much quieter situation in the Atlantic for hurricanes.

DW: So are those who point to Harvey and Irma as being climate change in action, are they mistaking weather for climate?

JC:  Oh yes, they’re mistaking weather for climate. Harvey and Irma were big storms, but they’re don’t really rank up there with the worst that we’ve seen in the last decade or the last century. There were some horrendous ones earlier in the twentieth century. Including really bad ones that hit Houston and Florida. These aren’t particularly unusual as far as hurricanes go. They’re top-20 kind of storms, but they’re not record-breaking in any way, apart from the overall rainfall from Harvey, which was really more of a fluke from the weather situation that allowed the storm to sit in one place for a very long time. There’s nothing unusual about this hurricane season or about Harvey and Irma. The US had incredibly lucky run of 12 years without a major landfall during this active phase of the hurricane cycle. We were incredibly lucky. Our luck is now broken. But it’s totally expected.

DW: Can I ask you finally about event attribution? Because there are people saying that hurricane Harvey wouldn’t have happened without climate change., there are people say that the heatwave in Russia was made ten times more likely because of climate change, or the drought in America was made X-times more likely. Can I ask you what you think about scientists who try and attribute individual events to climate change in a direct way?

JC:  The group that I like is really the NOAA group in Boulder, who looks at the historical record and tries to see is there anything unusual. Looking back a hundred years, is this exceptional in any way? If it is not particularly exceptional, given the record we have for the last hundred years, then it’s hard to argue that it is human caused climate change. Occasionally we do get genuinely record-breaking events. Then we need to trace back to what was the atmospheric dynamics, and whatever that contributed to that event and you need to tease it out. It needs a lot of detective work.

There is this new movement to use climate model simulations of natural variability, and then with natural variation plus human-caused global warming, but these same climate models they’re using can’t resolve these extreme events. They can’t produce hurricanes, they don’t have the right temperature distributions to provide heatwaves. It is just Voodoo statistics that they’re playing with these models — which do not have the capability to predict these extreme events in the current climate or an unperturbed climate anyways. I’m not very impressed with the model-based attribution arguments. Carefully-constructed diagnostic analysis and comparisons with historical events — to me those are of much more value.

DW: So we have to wait and see?

JC: We just have to wait and see. In the IPCC Fifth Assessment Report introduced this concept of time of emergence – when you would expect to see the statistics of the future climate breakout from the variability statistics of current climate, then they come up with something like 2050. We are not able to see a signal where the statistics would be genuinely different from what we have now. We’re not able to see that.

I don’t quite understand why it is important to attribute these extreme events other than to hysterically advocate reducing fossil fuels. In terms of trying to figure out how to manage extreme events and reduce our vulnerability, what’s causing it is almost a secondary concern. We’re not preparing for the events we have now, or the events we’ve seen in the twentieth century, let alone for the events that we might see in the latter part of the 21st century. If we have enough money for that extra resilience – wow, that would be great to prepare for even bigger events than we’ve seen. But adapting and preparing for the ones we’re seeing now would be a big step in the right direction to reducing our vulnerability to what we might be facing in the future.

Thinking that reducing fossil fuels is going to help with extreme events on the timescale of the 21st century is a pipe dream. Even if you believe the climate models, and we are able to drastically reduce fossil fuel emissions by 2050, we’re going to see miniscule impacts on the climate and the weather by the end of the 21st century. Any benefits would be realised in the 22nd and 23rd centuries. If we think we have enough wisdom and knowledge to what might happen in the 22nd and 23rd Century — personally I’d rather see us deal with here and now, and maybe focus on what we might be facing out to 2050. That seems a more practical and realistic goal, for what we should be trying to do. That’s my opinion.

Acknowledgement:  Thanks to Larry Kummer for the transcription and some annotations.