http://www.abc.net.au/catalyst/stories/4107264.htm
From 1975 to 1998 the world saw a rapid rise of global average air surface temperatures, linked to increasing greenhouse gas emissions. But for the last 16 years the rate of rise has slowed dramatically leading skeptics to question predictions of catastrophe. In this episode we find out 'what happened to global warming?'
Anja Taylor, ABC (Australia), October 16, 2014
GLOBAL WARMING PAUSEI
TRANSCRIPT
download video: mp4
NARRATION
17 years ago, a warm wind was blowing across the Pacific. As it blew, it pushed sun-warmed waters westward, piling them high to the north-east of Australia. When the winds eased, the warm waters washed back across the vast ocean, releasing masses of heat to the atmosphere in what became the mother of all El Nino events.
Richard Morecroft
The Florida storms are being blamed on El Nino.
News Reporter
..wild storms and heavy rain in South America...
News Reporter
A man-made permanent drought is...
NARRATION
It was 1998 and the climate seemed set on a frightening trajectory.
News Reporter
What the world is experiencing could be part of a climate shift.
NARRATION
But the years that followed didn't live up to predictions, leading to a crisis of confidence.
Christopher Monckton
They have been deliberately exaggerating the evidence, over-stating the case, frightening people, frightening even children.
Professor Judith Curry
The globally average surface temperature hasn't increased in any significant way since 1998.
Maurice Newman
In fact, can be argued since 2003 it has cooled off somewhat.
NARRATION
It became the most important question to answer in climate science today - what happened to global warming? It's a cold and blustery day in Boulder, Colorado. It seems a fitting start to a story on what's become known as the 'global warming pause'. It's a well-established fact that people are less likely to believe the world is warming when there's cold weather about. But it was also here at the National Center for Atmospheric Research that a distinguished senior scientist found himself at the centre of a climate conspiracy storm.
Dr Kevin Trenberth
This related to what was subsequently called Climategate in which a whole bunch of emails were stolen.
NARRATION
Among the Many hacked emails in the 2009 Climategate scandal was one from Dr Kevin Trenberth to a colleague. Sceptics seized on one particular sentence as written proof that climate scientists were involved in a large-scale cover-up.
Dr Kevin Trenberth
It was picked up as me saying that there was no global warming, somehow or the other, and completely misinterpreted and it just propagated all over the place - it was amazing to see.
NARRATION
Yet, the world didn't seem to be warming... at least not much. While the period from 1975 to 1998 had seen a rapid rise of global average air surface temperatures, in the years since, the rate of rise has slowed dramatically, leading a vocal minority to question predictions of catastrophe.
Professor Judith Curry
So we're getting this growing divergence between the observations and the climate model simulations.
Emeritus Professor Garth Paltridge
You have at least to consider the possibility that the models are not reliable for one reason or another.
Anja Taylor
On one point the sceptics were right - none of the models used in future climate projections predicted the hiatus. And while the slowdown for the first few years was written off as natural variability, lately it's become something to explain.
NARRATION
From the data he's been analysing, Dr Trenberth sees a planet heating up just as fast as ever.
Dr Kevin Trenberth
We can look at the energy budget of the Earth by looking at information from satellites that are flying above the atmosphere, which can actually track the incoming solar radiation from the sun, how much is reflected and how much the Earth is radiating back to space. It's not absolutely accurate, but it does track the year-to-year variations very well.
NARRATION
His calculations show our budget is continually in surplus - more energy coming in than leaving the atmosphere.
Dr Kevin Trenberth
Given that there's an energy imbalance, where does that energy go? How much has gone into the oceans? How much has gone into melting Arctic sea ice? Warming the atmosphere, warming up the land, changing evaporation and therefore changing clouds which can also change the brightness of the planet. And when we first did this, there was some quite substantial discrepancies that in some years we can't account for where the energy has gone.
NARRATION
And that was the cause of the frustration expressed in Kevin's email. Monitoring systems simply aren't sophisticated enough to track all of the heat exchanges on the planet.
Anja Taylor
The main focus in global warming has been air temperatures, because it's the easiest to measure and it's the temperature we feel. But it's a tiny fraction of the planet's total heat content and it's also highly variable.
NARRATION
As greenhouse gas emissions have risen over the last century, the long-term trend in air temperatures is obvious. But zoom in on the chart and you'll see fluctuations. These swings are put down to natural variability. The current hiatus is no different. But this time, climate scientists have been under pressure to pin down the exact cause. There have been several.
Dr Kevin Trenberth
So the sun went into a relatively quiet phase. In addition, there have been a number of small volcanoes that put debris into the stratosphere that blocked the sun. And what about the air pollution? China has been developing enormously - what has that done?
NARRATION
In total, aerosols and solar activity are thought to account for about 20% of the pause, but the biggest contender for where the rest of the heat is going is the one that's hardest to measure. The oceans absorb a whopping 93% of the world's excess heat.
Dr Kevin Trenberth
I've been working with the European Centre for Medium-Range Weather Forecasts, and they have developed an ocean-monitoring system that synthesises all of the information - sea-level measurements, the measurements from the floats, sensors that are measuring sea-surface temperature and so on - and that we've found is that after about 1999, a lot more heat is going deeper into the ocean. And this is unprecedented. Is this just a consequence of the change in the observing system or is it real? And I think we have good reason to believe that at some of this is real.
NARRATION
Multiple lines of evidence converge here in the Pacific, the largest and deepest ocean in the world.
Professor Matthew England
If you rotate the globe around, that's all you see for part of this hemisphere is just a big fat piece of ocean. The Pacific Ocean is a huge influence on climate.
NARRATION
Professor Matthew England has been key to nailing down how the Pacific has been dragging down world average temperatures.
Professor Matthew England
We had to look for something about the climate system post-2000 that was dramatically different to the climate system in the '80s and '90s, and one of the most dramatic things you see in the system is this flip in the Pacific Ocean. If ever you travel to the tropics in the Pacific Ocean, there's a prevailing wind from the east towards the west, and these easterly winds push a lot of the surface water across the West Pacific Ocean. If they remain for long enough, this water starts to get subducted into the ocean interior. During the '80s and '90s the winds were quite weak, not a lot of heat was getting subducted into the Pacific Ocean during that time and a lot of heat was remaining in the atmosphere.
NARRATION
Then came the massive El Nino event 17 years ago.
Dr Kevin Trenberth
In 1997-1998 there was a tremendous amount of heat that came out of the ocean, and we can measure it, and so the ocean actually cooled quite substantially. And so, we think that this may have then kicked the whole behaviour of the Pacific Ocean into a different mode.
NARRATION
The ocean once more began to build up heat. The change in the way the ocean either releases or draws in heat is part of a regular long-term cycle called the Pacific Decadal Oscillation. Each phase lasts around 15 to 30 years. When Dr Gerry Meehl from Boulder studied climate models with hiatuses, he discovered they linked closely with the negative phase of this pattern.
Dr Gerald Meehl
And sure enough the extra heat was going into the deeper ocean. So that was kind of the first tie we had, a tangible link to where the heat was going during these hiatus periods. And this connected then to stronger trade winds.
NARRATION
It was Matthew England who found these winds were unprecedented in strength this century.
Professor Matthew England
The winds are that much stronger than we'd ever seen before in the observations.
NARRATION
The winds are, in fact, being turbo-charged by abnormally warm waters in the Atlantic, as air races from high pressure to low, the winds push the warm surface waters west.
Professor Matthew England
So, over the last 20 or so years, the sea level over the West Pacific has risen quite dramatically above the global average sea-level rise, whilst in the East Pacific it's declined.
Dr Kevin Trenberth
And in this case, it's been piled up to such an extent that there's been a 20cm-rise in sea level compared with the Eastern Pacific. And that, to me, seems like a very large number.
Professor Matthew England
It's sort of reaches a breaking point perhaps where that heat then sloshes back to the East Pacific.
Dr Gerald Meehl
And that then adds to the warming from the increasing greenhouse gasses and you get real sudden increases of temperatures globally. Last time that happened was in the mid-1970s. Global temperatures warmed almost a half a degree Centigrade, which is almost half of the warming we got in the whole 20th century.
NARRATION
What that means is we're currently in the phase before the next global temperature jump.
Professor Matthew England
There will be warming out of this hiatus at some point in time - whether it's this or in five years' time, there's gonna be warming - and unfortunately, what we're seeing in the models is that the warming out of the hiatus is gonna be rapid, regardless of when that hiatus ends.
NARRATION
But a small minority of scientists disagree.
Professor Judith Curry
That's where I break with my colleagues. I just think there's a lot more uncertainty. We're now in the cool phase of the Pacific Decadal Oscillation, and I think that is the major thing that's causing the pause. And my understanding of the Pacific Decadal Oscillation is that we could stay in the cool phase for another two decades. So where does that leave us in terms of thinking that this sensitivity that we've deduced, largely based on this warming in the last quarter of the 20th century, during that period we were in the warm phase of the Pacific Decadal Oscillation.
Emeritus Professor Garth Paltridge
And this is a thought which is, for about 30 years people have tried to ignore because it takes away from the thought that most of the rise in temperature is due to increasing carbon dioxide in the atmosphere.
Professor Matthew England
Look, I agree that the warming in the '80s and '90s certainly would've had a component of Pacific natural variability to it. But it was beyond just that. So, if you think about the natural system without greenhouse gasses, it would see cooling of the atmosphere globally then warming in the positive phase, and we'd be flatlining over 100 years. We don't see that - we're seeing hiatus decades.
Professor Judith Curry
And there is one other possibility - that there is no missing heat. Changes in ocean circulation have changed the pattern of the clouds, which is reflecting more solar radiation and so the Earth isn't heating as much. So, unfortunately, the observations aren't quite good enough to distinguish between those two ideas.
Professor Matthew England
There's no evidence that clouds can account for this hiatus. Many things have occurred over the last 15 years that should've given us one of the coolest decades over the last 100 years. It's actually the warmest on record.
Dr Kevin Trenberth
We've seen that in Australia, we've seen that in the United States, all kinds of thousands of temperature records were broken.
Dr Gerald Meehl
A lot of the continental regions have continued to warm up. and we've seen an increase in, for example, heat extremes over a lot of continental areas, all the while that the global average temperatures haven't been doing much.
Professor Matthew England
Arctic Sea ice has declined dramatically, way beyond the projections. Sea level is rising faster than we projected even just five or ten years ago.
NARRATION
All things considered, there's been global warming pause.
Dr Kevin Trenberth
The whole of the climate system is really warming - it's just that the warming can be manifested in different ways.
Professor Matthew England
For some people, it's very easy for them to get this, but there are other people who are just absolutely obsessed with derailing the basic physics of climate change, and for them this poses a great little story that global warming's paused. I wish they were right but unfortunately they're wrong.
17 years ago, a warm wind was blowing across the Pacific. As it blew, it pushed sun-warmed waters westward, piling them high to the north-east of Australia. When the winds eased, the warm waters washed back across the vast ocean, releasing masses of heat to the atmosphere in what became the mother of all El Nino events.
Richard Morecroft
The Florida storms are being blamed on El Nino.
News Reporter
..wild storms and heavy rain in South America...
News Reporter
A man-made permanent drought is...
NARRATION
It was 1998 and the climate seemed set on a frightening trajectory.
News Reporter
What the world is experiencing could be part of a climate shift.
NARRATION
But the years that followed didn't live up to predictions, leading to a crisis of confidence.
Christopher Monckton
They have been deliberately exaggerating the evidence, over-stating the case, frightening people, frightening even children.
Professor Judith Curry
The globally average surface temperature hasn't increased in any significant way since 1998.
Maurice Newman
In fact, can be argued since 2003 it has cooled off somewhat.
NARRATION
It became the most important question to answer in climate science today - what happened to global warming? It's a cold and blustery day in Boulder, Colorado. It seems a fitting start to a story on what's become known as the 'global warming pause'. It's a well-established fact that people are less likely to believe the world is warming when there's cold weather about. But it was also here at the National Center for Atmospheric Research that a distinguished senior scientist found himself at the centre of a climate conspiracy storm.
Dr Kevin Trenberth
This related to what was subsequently called Climategate in which a whole bunch of emails were stolen.
NARRATION
Among the Many hacked emails in the 2009 Climategate scandal was one from Dr Kevin Trenberth to a colleague. Sceptics seized on one particular sentence as written proof that climate scientists were involved in a large-scale cover-up.
Dr Kevin Trenberth
It was picked up as me saying that there was no global warming, somehow or the other, and completely misinterpreted and it just propagated all over the place - it was amazing to see.
NARRATION
Yet, the world didn't seem to be warming... at least not much. While the period from 1975 to 1998 had seen a rapid rise of global average air surface temperatures, in the years since, the rate of rise has slowed dramatically, leading a vocal minority to question predictions of catastrophe.
Professor Judith Curry
So we're getting this growing divergence between the observations and the climate model simulations.
Emeritus Professor Garth Paltridge
You have at least to consider the possibility that the models are not reliable for one reason or another.
Anja Taylor
On one point the sceptics were right - none of the models used in future climate projections predicted the hiatus. And while the slowdown for the first few years was written off as natural variability, lately it's become something to explain.
NARRATION
From the data he's been analysing, Dr Trenberth sees a planet heating up just as fast as ever.
Dr Kevin Trenberth
We can look at the energy budget of the Earth by looking at information from satellites that are flying above the atmosphere, which can actually track the incoming solar radiation from the sun, how much is reflected and how much the Earth is radiating back to space. It's not absolutely accurate, but it does track the year-to-year variations very well.
NARRATION
His calculations show our budget is continually in surplus - more energy coming in than leaving the atmosphere.
Dr Kevin Trenberth
Given that there's an energy imbalance, where does that energy go? How much has gone into the oceans? How much has gone into melting Arctic sea ice? Warming the atmosphere, warming up the land, changing evaporation and therefore changing clouds which can also change the brightness of the planet. And when we first did this, there was some quite substantial discrepancies that in some years we can't account for where the energy has gone.
NARRATION
And that was the cause of the frustration expressed in Kevin's email. Monitoring systems simply aren't sophisticated enough to track all of the heat exchanges on the planet.
Anja Taylor
The main focus in global warming has been air temperatures, because it's the easiest to measure and it's the temperature we feel. But it's a tiny fraction of the planet's total heat content and it's also highly variable.
NARRATION
As greenhouse gas emissions have risen over the last century, the long-term trend in air temperatures is obvious. But zoom in on the chart and you'll see fluctuations. These swings are put down to natural variability. The current hiatus is no different. But this time, climate scientists have been under pressure to pin down the exact cause. There have been several.
Dr Kevin Trenberth
So the sun went into a relatively quiet phase. In addition, there have been a number of small volcanoes that put debris into the stratosphere that blocked the sun. And what about the air pollution? China has been developing enormously - what has that done?
NARRATION
In total, aerosols and solar activity are thought to account for about 20% of the pause, but the biggest contender for where the rest of the heat is going is the one that's hardest to measure. The oceans absorb a whopping 93% of the world's excess heat.
Dr Kevin Trenberth
I've been working with the European Centre for Medium-Range Weather Forecasts, and they have developed an ocean-monitoring system that synthesises all of the information - sea-level measurements, the measurements from the floats, sensors that are measuring sea-surface temperature and so on - and that we've found is that after about 1999, a lot more heat is going deeper into the ocean. And this is unprecedented. Is this just a consequence of the change in the observing system or is it real? And I think we have good reason to believe that at some of this is real.
NARRATION
Multiple lines of evidence converge here in the Pacific, the largest and deepest ocean in the world.
Professor Matthew England
If you rotate the globe around, that's all you see for part of this hemisphere is just a big fat piece of ocean. The Pacific Ocean is a huge influence on climate.
NARRATION
Professor Matthew England has been key to nailing down how the Pacific has been dragging down world average temperatures.
Professor Matthew England
We had to look for something about the climate system post-2000 that was dramatically different to the climate system in the '80s and '90s, and one of the most dramatic things you see in the system is this flip in the Pacific Ocean. If ever you travel to the tropics in the Pacific Ocean, there's a prevailing wind from the east towards the west, and these easterly winds push a lot of the surface water across the West Pacific Ocean. If they remain for long enough, this water starts to get subducted into the ocean interior. During the '80s and '90s the winds were quite weak, not a lot of heat was getting subducted into the Pacific Ocean during that time and a lot of heat was remaining in the atmosphere.
NARRATION
Then came the massive El Nino event 17 years ago.
Dr Kevin Trenberth
In 1997-1998 there was a tremendous amount of heat that came out of the ocean, and we can measure it, and so the ocean actually cooled quite substantially. And so, we think that this may have then kicked the whole behaviour of the Pacific Ocean into a different mode.
NARRATION
The ocean once more began to build up heat. The change in the way the ocean either releases or draws in heat is part of a regular long-term cycle called the Pacific Decadal Oscillation. Each phase lasts around 15 to 30 years. When Dr Gerry Meehl from Boulder studied climate models with hiatuses, he discovered they linked closely with the negative phase of this pattern.
Dr Gerald Meehl
And sure enough the extra heat was going into the deeper ocean. So that was kind of the first tie we had, a tangible link to where the heat was going during these hiatus periods. And this connected then to stronger trade winds.
NARRATION
It was Matthew England who found these winds were unprecedented in strength this century.
Professor Matthew England
The winds are that much stronger than we'd ever seen before in the observations.
NARRATION
The winds are, in fact, being turbo-charged by abnormally warm waters in the Atlantic, as air races from high pressure to low, the winds push the warm surface waters west.
Professor Matthew England
So, over the last 20 or so years, the sea level over the West Pacific has risen quite dramatically above the global average sea-level rise, whilst in the East Pacific it's declined.
Dr Kevin Trenberth
And in this case, it's been piled up to such an extent that there's been a 20cm-rise in sea level compared with the Eastern Pacific. And that, to me, seems like a very large number.
Professor Matthew England
It's sort of reaches a breaking point perhaps where that heat then sloshes back to the East Pacific.
Dr Gerald Meehl
And that then adds to the warming from the increasing greenhouse gasses and you get real sudden increases of temperatures globally. Last time that happened was in the mid-1970s. Global temperatures warmed almost a half a degree Centigrade, which is almost half of the warming we got in the whole 20th century.
NARRATION
What that means is we're currently in the phase before the next global temperature jump.
Professor Matthew England
There will be warming out of this hiatus at some point in time - whether it's this or in five years' time, there's gonna be warming - and unfortunately, what we're seeing in the models is that the warming out of the hiatus is gonna be rapid, regardless of when that hiatus ends.
NARRATION
But a small minority of scientists disagree.
Professor Judith Curry
That's where I break with my colleagues. I just think there's a lot more uncertainty. We're now in the cool phase of the Pacific Decadal Oscillation, and I think that is the major thing that's causing the pause. And my understanding of the Pacific Decadal Oscillation is that we could stay in the cool phase for another two decades. So where does that leave us in terms of thinking that this sensitivity that we've deduced, largely based on this warming in the last quarter of the 20th century, during that period we were in the warm phase of the Pacific Decadal Oscillation.
Emeritus Professor Garth Paltridge
And this is a thought which is, for about 30 years people have tried to ignore because it takes away from the thought that most of the rise in temperature is due to increasing carbon dioxide in the atmosphere.
Professor Matthew England
Look, I agree that the warming in the '80s and '90s certainly would've had a component of Pacific natural variability to it. But it was beyond just that. So, if you think about the natural system without greenhouse gasses, it would see cooling of the atmosphere globally then warming in the positive phase, and we'd be flatlining over 100 years. We don't see that - we're seeing hiatus decades.
Professor Judith Curry
And there is one other possibility - that there is no missing heat. Changes in ocean circulation have changed the pattern of the clouds, which is reflecting more solar radiation and so the Earth isn't heating as much. So, unfortunately, the observations aren't quite good enough to distinguish between those two ideas.
Professor Matthew England
There's no evidence that clouds can account for this hiatus. Many things have occurred over the last 15 years that should've given us one of the coolest decades over the last 100 years. It's actually the warmest on record.
Dr Kevin Trenberth
We've seen that in Australia, we've seen that in the United States, all kinds of thousands of temperature records were broken.
Dr Gerald Meehl
A lot of the continental regions have continued to warm up. and we've seen an increase in, for example, heat extremes over a lot of continental areas, all the while that the global average temperatures haven't been doing much.
Professor Matthew England
Arctic Sea ice has declined dramatically, way beyond the projections. Sea level is rising faster than we projected even just five or ten years ago.
NARRATION
All things considered, there's been global warming pause.
Dr Kevin Trenberth
The whole of the climate system is really warming - it's just that the warming can be manifested in different ways.
Professor Matthew England
For some people, it's very easy for them to get this, but there are other people who are just absolutely obsessed with derailing the basic physics of climate change, and for them this poses a great little story that global warming's paused. I wish they were right but unfortunately they're wrong.
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