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Home>Prism Update>Summer Seminar - Dr. Braaten

Global Temperatures

This is the picture of global temperatures back to the

(He is showing a graph)You can see on the right-hand side, over here, it has the global average
temperature which is about 15° Celsius. And over here, it's the change based on a mean from 1961-1990.

So you can see it really was much colder back during the latter part of the1800s and the early 1900s. Then began a warming trend where it kind of jumped around. But now recently, it's trending upward. And the peak here was 1998. This was associated with an El Nino. That's the largest global average to date. The past two years (2002 & 2003), have been tied for second, within a hundredth of a degree.

So we're now at a temperature of a little bit over 15.5°Celsius.

Temperature Anomalies

(He's showing a world map with red spots indicating temperature variations from average.) And here are the anomalies.
So an anomaly just means whether it is warmer or colder
than the average.And then the size of the circles, whether they be red or blue,indicates how much above or below that mean.

So you can see that 1993 (Note: he probably means 2003) was the second warmest year on record. Most of the planet had warmer than average temperatures which is very unusual. There's a lot of cooler areas, and a lot of warmer areas, but overall the mean is warmer.

In this case,it's very warm!And what interests us are the size of the red dots up in the polar region, are very large.So there are big changes occurring up in the polar regions.(Note: Red dots indicate it is warmer than average).

Climate Fluctuations

Fluctuations of climate really are not unusual. These are things that have
occurred throughout the past. When we talk about significant climate changes, we typically are looking at hundreds to thousand of years. If we look back just a thousand years, we see a period of warmth and a period that was very cold. Now we're going back into a period of warmth.

So, we have these periods of different climates. The first shown here, is a warm period, called the Medieval Climatic Optimum. Greenland was actually settled by the Vikings during this time.Then we have the Little Ice Age where Europe was very, very cold, and the weather during these periods was characterized by long, severe winters and short, wet summers. So it was a great challenge to grow things in Europe during this period. And this is also the time when the temperate glaciers, which are the glaciers in the Alps and in Alaska, actually advanced. They're now in retreat, but during this period, they actually advanced out quite a bit.

Unprecedented Temperature Change

Over the past 50 years, the trend in temperature change is unprecedented, even if you look back tens of thousands of years. We're in an interglacial period and you won't find any other interglacial period with this type of rise in temperature. It's a fast rise and it is unique, in the sense that it has NOT been seen in the paleoclimate record.

Greenland Ice Cores

(He's showing a photograph of an ice core). And last summer we were up in Greenland and they were drilling an ice core that went down over three kilometers, 2 miles or so into the ice. This is what they were extracting - this clear ice. This ice is from a depth of about 3050 meters. And the age of this ice is about 120,000 yrs. old. So, this ice was formed from snow that fell120,000 years ago.

This is back into a period that was very similar to the period that we're in
now climatically speaking. So this is sort of the Holy Grail of climate scientists. They want to get back into this period and understand what the temperature changes were, what the chemical compositions were, how much dust is in the sample, and all these other factors. That allows them to look at a period where there was a warming and then a very rapid drop into a cold period, which is really very similar to what we are in right now.

What Is Climate?

When we talk about the climate, what we're really talking about is a thermal balance of energies. We have energy coming in from the sun
it's heating the atmosphere, heating the ground, and some of it gets reflected back into space. Ther'es a thermal energy that's being radiated
out into space from the earth. And the earth has reached a balance now where this this temperature really doesn't really change much on the average from year to year. In fact, we typically see changes of less than a half a degree a year, and in some cases, even less.

So, really the earth itself is in radiative equilibrium. It's not going through wild changes at this point. It's going through very subtle changes.
And this radiative equilibrium temperature is due to the greenhouse gases.

If we didn't have any greenhouse gases in the atmosphere, then
the average temperature of the Earth would be about -18° C. And the reason for that is, simply, the radiative energy of the earth wouldn't be trapped and re-radiated back to the earth, it would just go back out to space. So, it would have a different equilibrium temperature.

What Are Greenhouse Gases?

The five main greenhouse gases are listed here. Carbon dioxide is the one everybody hears about but there are also some other ones.
Methane, nitrous oxide, chlorofluorocarbons, (which are refrigerants)
and then water vapor are the five main greenhouse gases.

Three of these are increasing quite a bit. With these types of gases there's a source and a sink and if these are in balance, there's no change in the overall concentration of the gas in the atmosphere.
But in this case, for those three gases, there's more going into the atmosphere than is coming out of the atmosphere.So they're building up.

Carbon Dioxide Levels

(He is showing a graph) This is something you have probably seen before -- the trend for carbon dioxide. These measurements, by the way, were taken at the top of Mona Loa Observatory in Hawaii, where it is away from any activity and the air is very clean, and it shows us the background concentration of carbon dioxide in the troposphere, the part of the atmosphere we live in.

So going back 40 years, from 1958 to about 1999, you see this trend,
kind of a saw tooth change, and that has to do with the seasons. We have more carbon dioxide coming out of the atmosphere during the summer time, when plants are using it in photosynthesis. In the winter time, when plants die off, we have a build-up of carbon dioxide. So the peaks represent winter-time and the little troughs represent summer time.

But overall the trend is upward. So essentially carbon dioxide is just accumulating in the atmosphere. We have this sort of an annual cycle of concentration change, but overall, it's accumulating in the atmosphere.

And right now, we're at, about 380 parts per million and it's estimated that in about 100 years, we'll be at 500 parts per million. If we go back to pre-industrial revolution, the concentration was about 280 parts per million. So we're effectively doubling it. Doubling the concentration from the mid-1800s. So, it's a very interesting experiment that's being performed on the atmosphere.

And this talk really kind of goes into what we can expect from this change. We don't really know all the details of what's going to happen, but I'll try to get into what we think is going to happen,and what we see happening right now.

Ocean Circulation & Cloud Cover

It's not just a simple balance of the concentrations of the greenhouse gases,there are other factors. The ocean stores vast amounts of energy and carbon dioxide and some of the earth's oceans' circulations really take about a hundred years to complete. So from the point that it starts the circulation pattern and goes around the world and comes back up might be 100-200 years.

So there's a lot of uncertainty of what effect the storage capacity is going to have in,say, 50 years,when we see some of this water come back.

Clouds play a big role too, and you can expect changes in cloud cover,
as the climate warms. It also really depends on whether the clouds are high or low as to whether they have a net warming effect or net cooling effect.

High clouds have a net warming effect, because a lot of energy is transmitted through the clouds, but is trapped by the clouds.
Low clouds, which are stratus clouds (or water clouds) have a net cooling effect on the surface.They reflect a lot of the energy
back to space and don't absorb or hold in as muchof the Earth's IR radiation.

Models and Observations

So models play a big part in climate prediction. But,you can't just look at the greenhouse gases alone. If you do that you get a crazy prediction that doesn't really fit anything that we've seen in the past.If you include the greenhouse gases and aerosols and solar radiation, you get something that fits.When you actually do the simulation going back in time,you get something that fits pretty well what we're observing now.

There's a lot of models out and they're all trying to make predictions
and they have a range of uncertainties, but generally what's been estimated now is that in terms of probabilities, over the next hundred
years, there's 90% probability that we're going to have a big temperature increase --1.7- 4.9 degrees Celcius!

If you look back, in the past hundred years we've seen a one degree change. So we're almost certain,90% probability, that we're going to see a big temperature change over the next hundred years.

Consequences and Threats of Global Warming

So what are the consequences? The PRISM work is dealing with sea level
change from ice sheet melt.You can expect more extreme weather events, more intense storms, more property damage, etc. Expect more heat waves and droughts, which are going to affect agriculture, and the ability to grow enough food to supply the world population. There will be greater potential for heat-related illnesses and deaths.

This is something we observed last year in France. A lot of people, over 10,000 people,died of heat stress in France alone. And then increased spread of infectious diseases. With increased temperatures, disease carriers can move into areas where they've never been
before and expose the people to things to which no one has been exposed before. This is a thoroughly frightening scenario, but there's a lot of uncertainty here and I won't talk further about it.

But in terms of the threat - people talk a lot about terrorism now. In fact
terrorism might be sort of a blip compared to this. This (the quote on the slide) came out recently from the UK's chief science advisor, Sir David King."Climate change is a far greater threat to the world than international terrorism. "So it could be a very big issue over the next
100 -200 years.

Ice Sheets and Sea Level

Our work here at PRISM deals with climate change in the ice sheets and sea level rise. Essentially the ice sheets are these huge repositories of
fresh water on the planet.If that water melts and goes into the ocean, then sea level has to come up and it's the only source of really significant sea level rise. If the ice sheets were gone, sea
level would not be able to fluctuate a huge amount. But with the ice sheets there actually is the potential for huge fluctuations.

Sea Level History
And so these are the numbers. Greenland holds the equivalent of 7 meters, so its melting could cause over 20 feet of sea level change.

Antarctica holds the equivalent of 60 meters, which could cause over 200 feet of sea level change. That's a huge potential for changing sea level.

Looking back over the past century, the rate of rise has been about 2 mm/year. And the expected rise, using some of the models that are out there is about a meter. So 48 + or - 40 cm over the next century.
We also have to realize that to people living in Kansas this might not seem like a big issue, but 60% of the world population lives in coastal areas.

EPA Estimates

There was a study that was done by EPA (Environmental Protection Agency) back in the 90s that said that ifthe sea level rises a meter, you're looking at costs to the US alone of 275-450 billion dollars. That was done a decade ago, so those numbers are way off already.

Also, with 1 meter of sea level rise - you're affecting 25 million people

Recent Changes In The Greenland Ice Sheet

(He's showing a map illustrating ice thickness in Greenland) These data comes from some of the work we are involved in. From the
flights on which Pannir flies his radar. But these are actually from laser altimeter measurements. These measurements have been repeated every 5 years and then normalized per year. What you're
seeing here are the measured changes in ice elevation in cm. per year.
The gray iindicates no change; yellows indicate an increase in thickness and the blues are a decrease in thickness.

So we see areas that really have no change.We see areas that have a positive change, and then we see these coastal areas,here, that are showing large, negative changes (i.e., losing ice). So those are what we're really focusing our interest on. Why are they changing so much?

What About Changes In Antarctica?

(He is showing a picture of ice shelf break in Antarctica and some graphs) Well, there are changes going on in Antarctica also. These are pictures from Antarctica. In March of 2002, there was a disintegration of an ice
shelf in Antarctica. And this is an ice shelf that had been there for
thousands of years.

Typically ice shelves expand outward and then they calve an iceberg off and the iceberg floats away and melts while the shelf grows a little more and another iceberg calves off, floats away and melts. That's what we've
normally seen with ice shelves. But what we saw with the Larson B ice shelf was that within a few days the whole thing simply disintegrated!
It just broke it into pieces. (Laugh) A huge part of this part of this ice shelf system that was along the Antarctic peninsula....

No one had ever seen anything like that before! And of course with the satellites we were able to capture that disintegration in great detail.

It had always been thought that these ice shelves play a role of blocking, or plugging up, the movement of the ice streams from the interior part of the continent. It was thought that if you pull the plug, so to speak, then
the ice streams would speed up. That was the theory.

Ok, now that theory has been tested, because the break-up of the Larson B Ice Shelf esentially pulled the plug on several ice streams. We can look at the change in speed of different ice streams leading into this Larson B complex, and in fact, you see huge changes after the disintegration.The acceleration was 3-10 times what it was before. So the shelf really was acting as a plug or "retarding mechanism". Now with the shelf gone, the streams are feeding much more ice into the ocean, up to a factor of10, than they ever have before in thousands of years.

So this is of big concern because as it feeds more ice into the ocean, you're going to get a change in sea level.

Ice Mass Balance

In terms of the ice sheet studies, we look at mass balance-- the net difference between accumulation from snowfall and loss from the melting and the calving of glaciers near the coast. And that difference or change in mass balance really reflects what sea level is doing. There are satellites now in space and more planned that will be used to find areas that
are changing very rapidly. Both NASA and the European Space Agency are involved in this.

The next question is: When they see them changing...Why are they changing? What's going on? So, the Larson B was one explanation for this change. But it is much more complicated than that. There are ice dynamics and climate fluctuations that are playing a role in the overall mass balance of the ice sheets.

That's where models come into play - to explain the current observations and to predict future changes. One of the key boundary conditions
on this mode is really the interface between the rock and the ice.
So we are interested in how the ice moves with respect to the solid ground. When we are talking about ice sheets, we are talking about ice masses that are grounded on land. Once they start to float (as icebergs), they've already contributed to sea level change. When they are on land, they're not contributing to sea level change -- it's only when the ice calves off into the water or melts that it can affect sea level.

Extreme Weather

So, I'm not going to go further into what actually we're doing, but I want to look at some of the other consequences of global warming. And one of these is extreme weather events. So as I mentioned earlier, these are something we would expect to see increase as the global temperature
warms up. But it's important to note that you can't point to one event
and say "Oh, it was hot last week," or "It was cold last week," or "We had a big storm last week."One event is meaningless in terms of climate change. It's very normal to have large fluctuations, soyou can't point to one weather or climate event as tied to global warming.

What you have to do is really take a long-term view of this. The longer, the better! I showed you our temperature records
go back 150 years. It would be nice if we had 500 years of temperature records, but we don't. So we just have to take what we have, and put them through a statistical analysis to see whether or not, we have a long- term trend. And to see whether it fits our expectations. So that's what we're going to do in some of these things.

Extreme Precipitation
One of them I want to look at is extreme precipitation events. You would expect, as the climate warms, more extreme precipitation events.
And what this means is that you're likely to have more precipitation fall over shorter intervals of time. So you get an increased frequency of heavy, extreme precipitation events.

In this case (he shows a graph of data), extreme precipitation was defined as more precipitation events. They went back in the records and counted the number of these events, normalizing it to the area, and then plotting it. There is a positive trend. In other words, it's increasing.
You see an increase in these heavy, extreme precipitation events.

Blizzards And Snow

So, do we see the predicted increase in blizzards and snowstorms with global warming? For colder locations, what we expect to see is an increase in the intensity and frequency of winter storms or snow storms.
And that's simply because in warmer climates you get more moisture into the atmosphere before it condenses. It's related to the saturation vapor pressure of water. And the saturation vapor pressure increases exponentially with temperature. So warming it a little bit increases a lot what the saturation vapor pressure is. And that simply means that water can exist as a vapor before condensing out.

Temperate locations here (on the graph) refer to the latitude. So the cold locations are places like Canada. Examples of temperate locations are the Dakotas and Minnesota. In those temperate locations, we expect actually to see a decrease in the frequency, but an increase in the intensity of winter storms. In other words, fewer storms but the storms that they get are much more intense.

There are some studies that have been done that showed that snowfall has increased in high latitudes in North America. And in the higher latitude regions up in Canada we do see an increase in snowfall but we also see that the snow accumulations are melting away much faster. In other words, the spring thaw is coming earlierand that's also something we would expect -- that the warming temperature will give you more snow but the snow is going to be melted away earlier.

Cyclonic Winds

Ok, what about storms? There's also some work that has been looking at mid-latitude storms -- some meteorologists call them mid-latitude cyclones. What we define as a mid-latitude storm is simply a storm with fronts. So there is a warm front and a cold front in a low-pressure center, you know, that potentially has very strong winds and significant weather associated with it.
If we look back over the past couple of decades, we have observed an increase in the frequency of intense storms in the North Atlantic -- the northern North Atlantic (i.e., from the equator to the north) and Western Europe. There has been an increase in the frequency of these very intense storms. And with these storms you don't only get a lot of precipitation, but you get very strong winds that can do damage, tear down trees and topple cars, and tear down power lines, and things like that. Europe has seen quite a few of these storms recently and that's unusual. Or, at least, the numbers they've seen are unusual.

However, if you look to the South in the North Atlantic, (South of 30° North in the North Atlantic), you actually see a decrease in the frequency and intensity of storms. It's not really clear, why that is.

Hurricanes and Tropical Storms

Tropical storms and hurricanes are typically formed near the equator in very warm ocean temperatures and really don't have any fronts. They are essentially storms without fronts. And they form near the equator or within 10°-20° of the equator and then they migrate to the north. They don't form in all ocean basins, but they form in a many of them. So if we look at this (slide), this is just for the North Atlantic.

If we look at the trends going back a hundred years or so, and you look at all hurricanes or even look at just the most severe (category 3-5) hurricanes, you don't see much of a change.

So, what about increased frequency of drought? Everyone has heard of the Dust Bowl of the 30s. It was such a huge event, spanning 6 years or more, that scientists really can't determine or discern any trend. If you look at the trends from the early part of the century, you get this huge spike where the Dust Bowl was and, you know, if you are trying to fit a trend -- it just doesn't work. So we don't have much information about whether droughts are increasing.

To conclude, global warming and its implications are potentially very serious. I think, if anything, that is an understatement. I think its going to be extremely serious. It's going to be an issue that requires world attention. It's going to require sacrifice.

Sea level rise, changes to the ice sheet? Yes, we're seeing that.

What about the signal in other weather events?

  • More extreme precipitation events? Yes, we are seeing that.
  • Increased intensity of snowstorms? Yes.
  • Increased frequency of mid-latitude cyclones? Maybe, we see it in certain regions, -- we don't see it in other regions.
  • Increased frequency and intensity of tropical storms , hurricanes? No. Definitely we definitely don't see a trend here.
  • Increased frequencies of droughts? Again, maybe. Because of the dust bowl, we don't know.

And really, it's probably going to take decades before we know exactly what the human contribution is on these weather events. And even on the ice sheets and how the ice sheets respond to natural climate fluctuations.


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