Monday, July 4, 2011

What NCAR's Kevin Trenberth actually said at 2004 Harvard News Conference

This post is sort of an addendum to a post at regarding the echo-chambers accusations, fueled by Chris Landsea's IPCC resignation letter, that Kevin Trenberth has lied. Interestingly, when reading the actual transcript I can't find where, or what Trenberth was supposed to have lied about.

I went through the transcript and culled out important statements. Since I can't share so many quotes at SkepticForum, I figured I'd post the collection over here in case anyone wants to read what Trenberth actually had to say as opposed to just accepting others agenda driven mis-characterizations...
{Although if you have the time it would be much better to read the whole thing, click below}

Hurricanes and Global Warming News Conference

Center for Health and Global Environment
Harvard Medical School
October 21, 2004
Highlights from the Verbatim Transcript

Epstein: (medical doctor trained in tropical public health and Associate Director for the Center for Health and Global Environment at Harvard Medical School.)

{10/21/04 news conference - 2}

Four things we know are true from the 2001 Intergovernmental Panel on Climate Change. We know the climate is changing. Two, that humans are having an influence. Three, biological systems are responding on all continents, and weather is becoming more extreme. This alone, these statements, tell us that by deduction we've got to understand all events that we are seeing in terms of climate change and natural variability.

We cannot isolate one event and say "Oh, this is natural. This is climate." Everything is a function. I know this may sound new and heretical but that's the conclusion that climate and baseline is changing.

Since 2001, we know a lot more about the system. We know more about the deep ocean warming throughout the world. We know that surface pressures and winds are affected and polar winds are affected so that gradients are set up and so that storms can become more intense and are seeing these swings back and forth from dry periods to wet, et cetera.

McCarthy: (professor of Oceanography at Harvard University and as mentioned in the introduction co-chair of the Intergovernmental Panel on Climate Change Working Group 2 on impacts in the last assessment, which concluded its work in 2001)

{10/21/04 news conference - 3}

We know that the earth's temperature and precipitation patterns are changing as a result of changes — not only those attributable to natural variability but also attributable to the greenhouse gas condition that's accumulating in our atmosphere.

On every continent it is now evident that there are impacts from these changes in
temperature and precipitation and while some of those changes, some of those impacts, rather, are seen as positive, many of them are negative and disruptive. We see this in every aspect of natural ecosystems, but also in human socio-economic systems.

{...} In addition, there are increasingly intense precipitation events. Many of these we have just heard reference to, but similarly the projections for the future show that this is going to become increasingly common.

{...} The one aspect of this ongoing climate change that continues to receive less attention than it deserves is how the warmer world will lead to more extremes in weather and particularly these heavy precipitation events, extreme wind events, and more hot, dry periods as well.

{10/21/04 news conference - 5}

Trenberth: (from NCAR, the National Center for Atmospheric Research. Lead author on the 2001 IPCC report for Working Group One.)

Let me focus then on the science of climate change and the physical aspects of the climate change that are going on. The first key point, as Jim McCarthy said, is that the atmospheric composition is changing due to human activities. There's a buildup of carbon dioxide; it's around 31, 32% higher than pre-industrial levels. Global warming is happening and there is a lot of evidence for that, as others have already stated, and the global mean temperature is increasing.

One thing I would pick on, in particular, is that global sea level has risen about an inch and a quarter in the past ten years. This is good information — the first time we've had global information from satellites using a process called altimetry. Now most of this rise in sea level is due to expansion of the ocean as it warms up, and maybe 20 to 35% is from melting of glaciers.

So the sea surface temperature is rising globally. It's been about 1 degree Fahrenheit over the 20th century and it's risen in particular in recent times in the Atlantic and other regions, of course, that affect hurricanes. At the same time, water vapor amounts have increased and the empirical evidence suggests that water vapor in the atmosphere goes up about 10% [7% overall] for every degree Celsius—or say about 2 degrees Fahrenheit—increase in sea surface temperature in the atmosphere.

{10/21/04 news conference - 6}

And of course this is the fuel for the hurricanes and it also means that the hurricanes end up dropping a lot more precipitation and rainfall as a result. And so the environment in which these hurricanes form is changing and it's changing in ways that provide more fuel for them through the water vapor and the changes in sea surface temperature.

And another example aside from the ones over near Japan is that on late March 2004
there was a hurricane in the South Atlantic off the coast of Brazil. This was the first of its kind and it's clear evidence that things are changing.

In general, the changes in the tropics are such that more storm activity is favored, but it's very difficult to say whether or not these are going to be individual thunderstorms or hurricanes. And in general throughout the United States in the 20th century there was an increase in heavy rainfall events of about 7% and very heavy events, which is the top 1% of all events, were up about 20% in the 20th century. And so this is an indication that in general rainfall events are apt to increase.

There are several factors that go into making hurricanes. They're really a collective of thunderstorms and they need a disturbance that hangs together. And we are not able to say what global warming is likely to do to that, and so there could be a trade off between individual thunderstorms versus actual hurricanes. It also requires—this actually requires a favorable atmospheric circulation.

This relates to things like whether the wind will blow it apart or wind shear will cause it to collapse before the hurricane actually forms. And we can't say anything really about the tracks which make the hurricanes hit the U.S. or miss the U.S.—whether they [make] landfall or not. What we can say is that the high sea surface temperatures of water vapor make for more intense storms and so this is consistent with the evidence that we're seeing. And so this is the main link with global warming that we can establish at the current time.

And so this is supported also by the modeling evidence and the theoretical evidence.
There was a certain amount of activity regarding a paper that came out recently by a group headed by Tom Knutson at the Geophysical Fluid Dynamics Laboratory. And that supports the idea that indeed hurricanes are apt to become more intense in the future. So a key consequence, I think, is certainly perhaps increased damage from winds, but I think the biggest consequence is likely to be more heavy rains and flooding.

Patrick O'Driscoll, USA TODAY: Is what you're saying now much of a departure from what the IPCC report said three years ago, four years ago?

Trenberth: I think the evidence is mounting as Jim McCarthy suggested, and I refer to the hurricane off of the coast of Brazil. You heard also from Matthias that there is unprecedented activity out in parts of the Pacific, the far western Pacific, and now we have a series of seasons, very vigorous seasons ever since 1995. Let's see, I think seven of those—seven of the last ten years—has been above normal in terms of hurricanes. So this kind of evidence is pointing more in the direction that these extremes are occurring and are having a real impact on society.

Epstein: If I just second that and say — yes, we knew these things as of 2001, but now we've learned a lot more. Ruth Curry at Woods Hole [Oceanographic Institution] has published a paper showing that the tropics in general are becoming warmer and saltier as they evaporate and we're seeing changes towards the poles of fresher and cooler water. So there's a dynamic in the Atlantic Ocean, it's the same thing with all the oceans in terms of changes in this distribution of heat and salt.

And so that creates a belt out of which these hurricanes can be fueled. In general we're seeing more outliers, and that's what I was describing — more events that are even greater than one or two standard deviations from the mean. Like the heat wave last summer, like this state of hurricanes.

{10/21/04 news conference - 8}

McCarthy: I would just like to make one additional comment. I think one way to answer that question is, what we're seeing is happening more quickly than had been projected just four or five years ago, and that's true of the rate of ice loss in Greenland, the rate of loss of ice in Antarctica, but also the extreme events.

And if you look at the data the four of the last six years are now the warmest years on record. So, as we look ahead and we anticipate these changes, the temptation is to think that they'll be smooth changes. But if anything they're accelerating and they are more irregular than we had thought likely and therefore more disruptive.

Moderator: Is there a follow-up question there?
O'Driscoll: Just a brief one. Again, for many of you, for laypeople out here who may look at this and say, "Well, couldn't you chalk this up to just natural variation and deviation?" I mean, it's an awfully short period of time we're talking about here where we've seen these admittedly extreme changes. What's to say that it won't revert in coming years?

Trenberth: That's a very good point, and certainly in the Atlantic there's no guarantee that this is going to continue, because in the Atlantic there is large, natural decade-to-decade variability in hurricane activity and we know the way in which the ocean works in the Atlantic is that it's apt to favor this kind of thing. There will be on and off periods.

But at the same time within that, now superimposed on that natural variability, is also this longer-term trend that we associate with global warming. Even a year-to-year basis — there can be a year with more hurricanes or fewer hurricanes, depending on things like El Niño events in the tropical Pacific.

And indeed, as we've had more hurricanes in the Atlantic in recent years, there
have actually been fewer hurricanes in the far Eastern Pacific — you know, off of the west coast of Mexico and so on—and so there is a competition around the tropics as to where hurricanes tend to occur, and this natural variability is certainly going to continue.

Usha McFarling, Los Angeles Times: Elaborating on that last question, I'm just—can you be clear, are you—I know in the Knutson paper they are talking about perhaps increases of 5% of wind speed in 80 years,

{10/21/04 news conference - 9}

but this stuff doesn't seem to imply that what we saw in Florida may be due to climate change because of warmer sea surface temps. And I'm wondering — the hurricane researchers are saying what happened in Florida, they don't believe is linked to climate change—it's definitely more that decadal variability and just bad luck with the tracking of storms towards Florida instead of out to sea or elsewhere. So, maybe if you could be clear on what—what are we saying here? Are we saying that what we saw in Florida may be an indication on what's in the future, or are people implying that perhaps Florida was caused by climate change and we're already seeing the changes now instead of 80 years from now? Thank you.

Trenberth: That's a very good question, and I think one of the reasons we've got this press conference is to perhaps try to add a little bit to other statements that have been made by hurricane forecasters. Now as I mentioned before, there is a lot of natural variability and decadal variability in hurricanes, and as Matthias mentioned it's impossible in fact for researchers to tie an individual hurricane or even four hurricanes to global warming as such.

But as we... have mentioned, there is a much larger pattern going on and it's not just in the Atlantic but in the western Pacific and it's also other rainfall events, severe weather events across the United States, and so on. And so it's part of a larger pattern which is consistent with the sorts of things we expect with global warming.

With global warming a lot of the heat goes into driving the hydrological cycle, evaporating moisture, putting moisture into the atmosphere, which then gets rained out and there's more moisture lying around. Then the rain events tend to be heavier. And at the same time in places where it's not raining, there is more evaporation and so the droughts tend to be stronger as well.

And so ironically you can have stronger rainfall events and stronger droughts at exactly the same time and caused by the same phenomenon.
And of course we're well aware that there's a major drought going on in the southwestern parts of the country. And so, it's just larger context that we thought was missing and needed to be brought to bear to indicate that this is a real risk and it's something we are going to have to deal with as we move into the future.

Epstein: {...} what Kevin's comments help us understand is that we can understand the dynamics under them. They're making sense in terms of the warming

{10/21/04 news conference - 10}

of the ocean, drying out of land. As surfaces of the ocean and the land heat up it changes the pressure and the pressure gradients that's changing wind speeds. As I mentioned, we're now seeing increased wind speeds around both poles. So we're seeing some changes in temperature and pressure and pressure gradients and wind and weather patterns that are consistent with the changes we know to be associated with warming of the ocean and climate change.

Juliet Eilperin, Washington Post: I think you mentioned it briefly, but I just wanted to check again. Can you just explain the dynamics when sea temperature, sea surface temperatures, rise, then water vapor is increased? In other words there is more water evaporating and how does that shift the dynamics again? Can you just go over that one more time?

Trenberth: Certainly. Well, we know from a very fundamental physical law that as you warm up the atmosphere it can hold more moisture and so if you keep the relative humidity constant then for every 1 degree—I'm sorry this is in Celsius—1 degree Celsius there's a 7% increase in the water-holding capacity.

Now empirically, when we look at what's going on over the North Atlantic, for every 1 degree Celsius increase in sea surface temperature it's actually about a 10% increase in the water vapor in the lowest 20,000 feet of the atmosphere. So we take the column integral, it's not just the humidity of the surface we're looking at, but also throughout the lower part of the atmosphere.

And so that has gone up by about 5%, for instance, in the last fifteen years from the very good measurements that we've got now over the ocean from an instrument called the—well, it's a microwave instrument—and so the water-holding capacity goes up and the empirical evidence suggests that the actual amount of moisture in the atmosphere goes up, and this is, of course, the fuel for any thunderstorms and tropical storms.

Epstein: As I learned from Kevin you've got a push-pull on the water cycle. As water warms, the oceans warm, they evaporate faster. As the atmosphere warms, it can hold more water vapor. So water is warming, water vapor's rising, and ice is melting. These are the three parts of the hydrological cycle that are changing.

{10/21/04 news conference - 11}

Trenberth: Yes, certainly. If you just look at what's going on in the Atlantic the record has a lot of variability from year to year. Some of that's associated with El Niño—this is Kevin Trenberth from NCAR again—and also there's this decadal variability which may well be associated with things like this thermohaline circulation. That was the change in circulation throughout the Atlantic that was a key in the movie called "The Day After Tomorrow." And so that's a form of natural variability, but it may well also be affected by global warming.

And if you simply take that narrow view, then it's very hard to find a global warming signature in the record. And we're suggesting here that maybe the main signature is not so much in the frequency, the number of hurricanes, but rather more in the intensity of hurricanes and the very heavy rainfall events. Certainly there is a very clear signature in the United States, and east of the Rockies in particular, where heavy rainfall events are increasing and a good fraction, a fraction, of those are associated with hurricane events.

Chris Crisler, Florida Today: We're rather hurricane-centered down here as you might imagine, and given—you do seem to be talking about a broader trend than perhaps an increase in more extreme events. So, I just want to clarify—you can't be more specific about, say, number of storms, but storms we do get might be more intense, and you can't be more specific about tracks necessarily at this point.

Trenberth: One of the things that we did say in the 2001 report is that certainly the environment in the tropics becomes one which favors more storm activity in a general sense, but it's very difficult for us given our current knowledge to say whether it's going to be a whole lot of individual thunderstorms or a collective of thunderstorms where they get organized into a tropical storm or a hurricane.

And it could be that as we move into the future that we end up with a whole lot of thunderstorms, but of course Florida gets a lot of thunderstorm activity as well, and so you can also expect that kind of thing, as well.

{10/21/04 news conference - 17}

McCarthy: {...} One of the realizations of the late '90s work that is summarized in the IPCC documents is that that's not a choice we can make any longer. We have embarked upon a path and are now at a point where these impacts are all about us and will continue to arise. Many of them negative, some perhaps positive. There certainly are some positive ones, but it's the negative ones we are talking about today that are so disruptive to lives, livelihood, and property, and indeed much of what we have done in the way we have used our habitable areas has contributed to this.

Moderator: You've been listening to a tele-news event sponsored by the Center for Health and the Global Environment at Harvard Medical School.
~ ~ ~ ~ ~ ~ ~

Related sites on the World Wide Web:
Experts to Warn Global Warming Likely to Continue Spurring More Outbreaks of
Intense Hurricane Activity (news release)

Center for Health and the Global Environment, Harvard Medical School

National Center for Atmospheric Research

Swiss Re

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