Alex Tardy, Meteorologist, National Weather Service
Daniel Cayan, Research Meteorologist, Scripps Institution of Oceanography
CAVANAUGH: Our top story on Midday Edition is the heat. It's supposed to be hot in the summertime, but this extended period of heat and humidity in San Diego seems extreme. And it's nowhere near as extreme as the kind of heat and drought conditions the rest of the country has been suffering through. So when does the daily weather begin to reflect the trends of climate change? My guests, Alex Tardee is a meteorologist with the national weather service here in San Diego. Welcome to the program.
TARDEE: Thanks for having me.
CAVANAUGH: Daniel Cayan is a meteorologist with Scripps institute of oceanography. Welcome to the show.
CAYAN: Thanks Maureen.
CAVANAUGH: We all know that it's hot, but how hot is it?
TARDEE: To put it in perspective, if you feel like the summer has been hot, those inland, day and day of 100-degree. Its. Eight-days for areas like Riverside where they have been above 103 degrees, eight-days in a row. With the rest of the country, July turned out to be the hottest we've seen since the mid-19-thirties. And since January 1st of this year, the whole entire country, hottest we've seen ever on record. We've been spared some of the real severe heat like you mentioned in your introduction. And certainly drought and heat go hand in hand, and have been feeding off of each other.
CAVANAUGH: What are the dangers of an extended period of very hot weather? We know that some people are at risk because of the heat, because of extended periods of being in like a nonair conditioned place. What about the fire danger here in Southern California?
TARDEE: There's a lot of impacts. Starting with the fire danger, the more days you have with a lot of heat and relatively lower humidity, you're drying out the vegetation. And the more you have that, the more you're increasing the chances of being sensitive to a fire. If there's a fire that starts, then you worry about is there going to be some wind to follow it. There's been some fatalities in Southern California directly related to heat, andes toens of hospitalizations. Not just in the deserts, but other parts of the area too, in the valleys.
CAVANAUGH: How does this summer compare tow the rest couple of years? I remember complaints. There was a summer that never developed.
TARDEE: You're exactly right. Last year was kind of a moderate summer. And we had a couple good hot stretches in July and August of last year, which is normal. Two years ago, we couldn't see the sun at the beaches, we had the gloom going all the way through August. This year in Palm Springs, they're running almost 5 degrees above normal. When you average all the days in, one or 2 degrees above normal is noticeable to the average person.
CAVANAUGH: What is causing this heat wave? Is there Homepost locked over the area? Is that what it is?
TARDEE: That's a good question. Since March, we've seen normally strong Homepost, when we talk about Homepost, a dome of warm above us, that's compressed over the land. You add those two together, it's just been a much stronger system than normal, and persistent. March broke records, and July was right behind it.
CAVANAUGH: Daniel, is this extreme heat a sign of climate change?
CAYAN: Well, it's consistent with climate change. But every short-term event is usually composed of a large fraction of natural variability, and as Alex was mentioning, with the particular form of the atmospheric circulation, that's a major ingredient of what we've seen. And likely even without human influences, we would be -- it would be warm in this situation. However, the greenhouse gas concentration in the atmosphere is the cause of increased heating at the surface, has been building CO2 increases of more than 1/3 now over preindustrial levels and projected to very likely double if we're lucky by the end of the century, and possibly eclipse that. So the presence circumstance is probably a sign of things to come. And unfortunately even though we can't totally attribute this to this particular event to climate change, it looks like in the future these kinds of events will be more common place.
CAVANAUGH: I do want to invite our listeners if they'd like to join the conversation. When we take this summer across country, the kinds of statistics Alex was talking about, drought and extreme high temperature, the warmest gentleman the United States has on record, that is also consistent with the kind of trend you're talking B; is that right?
CAYAN: It is. It's important to say that what we're seeing across the United States, Lrecord-breaking for July, and so forth, in its pattern, it's not unprecedented. We had enormous droughts and heat spells in the 30s and in the 50s which are kind of an analog to what we're skiing this year. It appears by taking this larger scale perspective, the global perspective, that there's -- many of these extremes that are occurring today at a rate of occurrence that probably does exceed what we would expect from just a natural climate variability perspective. So it's quite likely is that climate change is playing at least an incremental role.
CAVANAUGH: A Scripps institution report, they participated in several reports, one said summer months of extreme heat will be the norm by 2060. What led you to that conclusion?
CAYAN: Well, in looking to the futures, we used the same kind of models that Alex uses in projecting the weather days in advance. But these are run over decades into the future to understand what further loading of greenhouse gas into the atmosphere will be. Virtually every model run internationally, and now there's more than 20 that have provided information, indicate that our climate is warming, there's a range of possibilities. This is not a pure, exact science, but the range of warming cast in today's ups and downs what wee seen historically is actually quite remarkable. Looking at those models going forward into the middle part of the century, here in California, we are seeing projections of 2 degrees Fahrenheit to about 5 degrees Farenheit. Alex mentioned the fact that the man on the street and myself included can feel maybe more than a degree when it's averaged over a season or a year, so this is at least twofold of that, and perhaps even more. As you shift that average climate forward and superimpose the kind of event that we're seeing this last week, the extremes are going to get hotter. They're not only going to get hotter, but probably longer in duration. So there is a concern there.
CAVANAUGH: Rich is calling us from San Diego. Welcome to the program. Okay. He wanted to ask you when you're making those models, predicting the outcome of climate change in 50 years on and so forth, do you take into consideration the kind of mitigation that states like California are trying to do when it comes to greenhouse gases?
CAYAN: The models are run under a variety of scenarios, how greenhouse gas emissions may unfold not only here in California but even globally because we are in terms of the atmosphere a global system, and it's a well-mixed atmosphere. So we're all sharing. But again
the scenarios go from optimistic that would follow if other regions followed California's lead, and other scenarios that are not very optimistic. So we hook at the gamut of those, and one reason for the broad range of potential futures in terms of temperature is the fact that that folds in this range of scenarios, rather than just business as usual.
CAVANAUGH: I want to ask you both a question because I think this is what a lot. People who have lived in San Diego for at a while have noticed. It seems that humidity as increased in San Diego in receipt years. Is that just something that's part of our dilutional system? Or do you keep data on changing humidity?
TARDEE: We do keep data on it. With the drought that we're seeing right now, it's the worst drought we've seen since the 1950s. And a lot of these accumulate into a greater impact. We have seen an increase in humidity. It's a subtle increase, but it's there, it's real.
CAVANAUGH: Is there any chance that San Diego will start to people more tropical as it gets hotter and more humid?
CAYAN: Well, we do live under the influence of north peculiar high, which is a pretty imposing force of a trier climate here. So I wouldn't expect that we're going to turn into Miami. But as things get warmer, and the hot spells that we have had recently, 2006 was a great example, where nighttime temperatures and humidities were exceedingly high, we've seen the evidence of heat waves becoming more than historically, and we've seen the lack of cooling at night, which of course a lot of us have experienced in the last week or so.
CAVANAUGH: Many of us are testimony with el NiÒo. Is that affecting what's going on now?
TARDEE: If you look at the current pattern, when you heat up the land and makes the Homepost stronger, you're actually changing the weather pattern. If you look just to your east the past week, there's been an increase in thunderstorms. You're adding moisture when you heat the environment and you dry that monopoly up from the south. In terms of El NiÒo, we typically see more of an impact as you get up to the winter months. There are southern impacts. We probably aren't seeing that necessarily right now over our region. We're seeing the impact of a large kale drought in the United States, a big dome of Homepost that's positively fed from that drought and changing our weather pattern just slightly, but bringing more moisture into our region, and more hot weather.
CAVANAUGH: What is the long-term forecast for San Diego? When is this heat wave going to end?
TARDEE: I'll very them in reverse. In the short-term, it electric like you're going to have a cool-down, but we're going to heat back up this weekend. Maybe not quite at the levels we were at, but very close to those levels it. Long-term projection, we have some relief in terms of more storminess for the winter, probably starting November for at least the very good probability of normal precipitation. We are disciplining an El NiÒo event which would bring a normal precipitation pattern, but it also could bring milder temperatures in the winter months with more cloud cover.
CAVANAUGH: Thank you both.