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Extreme weather: the records which are being -

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Robyn Williams: Here's a QI question for you; which team in Australian broadcasting has the best looks combined with the highest academic qualifications? The answer at the end of this Science Show. Second question; did you notice what President Obama mentioned for the first time in eons?

Barack Obama: We want our kids to grow up in a country where they have access to the best schools and the best teachers, a country that lives up to its legacy as the global leader in technology and discovery and innovation, with all the good jobs and new businesses that follow. We want our children to live in an America that isn't burdened by debt, that isn't weakened by inequality, that isn't threatened by the destructive power of a warming planet.

Robyn Williams: Did he say 'warming planet'? Is it safe to mention such things again in America? In a week when two huge storms battered New York, what is going on? Here is renowned climate scientist Dr Kevin Trenberth.

Kevin Trenberth: There's a very good reason for talking about the extremes because when we think about climate change and how we actually experience it, it's mainly through the changes in the extremes. It's not through the global mean temperature. The global mean temperature has gone up 0.8°C. You probably can't perceive 0.8°C. But going along with that with a warming climate there are more high temperatures and heatwaves and wildfires and other consequences, but you expect that you will break records on the warm side and the cold side at the same rate.

And in the's the ratio of the cold records and the warm records: in the 1950s it was about 1 to 1, it was less than that, the cold records were actually exceeding the warm records in the '60s and '70s. And in the '80s it was edging up more to more warm records. In the '90s it was about 1.4 to 1, and by the 2000s it was about 2 to 1. And then if we look at more recent times, if we look at 2010 it's about 2.3 to 1, 2011 it was 2.7 to 1, and for the first six months or so of this year it was running at a ratio of 9 to 1. So this is where there's clear evidence of climate change. We are breaking records on the high side, and this is not something that would occur in an un-changing climate.

Robyn Williams: Dr Kevin Trenberth is head of climate analysis at the National Centre for Atmospheric Research in Boulder, Colorado. He lists some of the extreme events we've endured recently.

Kevin Trenberth: An Australian example, 2009 on 7 February, Melbourne got up to 46.4°C. For the Americans in the audience it's 117°F. There was drought for about two months. Prior to this there were intense heatwaves, very strong winds, there were bushfires galore and over a million acres were burnt, there were 173 deaths, and 2,030 houses were destroyed. This is so-called Black Saturday on 7 February, and it so happens I landed in Melbourne on 7 February for a conference at that time and I got to see some of these wildfires right up close and personal, unfortunately.

The second example is Russia. So this is a year or so later in August of 2010. This is a famous region just off of Red Square, St Basil, but it's all hidden in the smoke, and the wildfires were all over the place.

But at the same time, it turns out, there was flooding in both China and India, and spectacularly so in Pakistan. There was something like 300,000 people that were displaced as a result of the flooding that occurred at the same time that the heatwave was going on in Russia.

And so 56,000 deaths, $15 billion in damages estimated, over 2,000 buildings destroyed, there were major crop failures, especially wheat. This had an impact on the international marketplace for wheat. The cost of basic staples went up throughout the world and especially it went up in the Middle East, Northern Africa, and it led some sense the Arab Spring was partly a consequence of these increases in prices and the tensions that resulted.

Robyn Williams: So why the extremes? Dr Trenberth points out that small temperature rises accumulate. There's more energy in the atmosphere. Normal events become more violent, like this:

Kevin Trenberth: So when we go to 2011 there was tremendous flooding along the Mississippi River as well, going from April to May, and it turns out that this was the third 500-year flood in the last 20 years. Well, of course they are not 500-year floods anymore. That's one of the consequences. And there were a tremendous amount of tornadoes, a huge loss of life in Joplin, Missouri, and a little bit later, by June Arizona was on fire, the worst wildfires in Arizona, and there was a major drought, and the worst wildfire in Texas, 600 homes were lost in this particular fire, and record heat in places like Dallas, over 40°C.

And then in 2012...I live in Boulder, Colorado, there was the so-called Waldo Canyon fire where there were 346 homes lost, and this is the High Park fire near Fort Collins, 259 houses lost. Somewhere here, let's see, right there is my institution, NCAR, the National Centre for Atmospheric Research, and about 1.5 kilometres away there was a wildfire that actually shut down NCAR for a couple of days because the air quality, the smoke was just too great and you couldn't run the computers or anything like that.

And so this year...this is the average temperature. The average temperature was over 35°C in many regions. It finally beat out the 1930s, this was the so-called dustbowl era in the United States, and this has always been hanging over us, that there was this dustbowl era, and it was much drier back in here than it was with this tremendous drought that we've had even this year in the United States. But we broke most of the records that occurred back in the 1930s.

And so with regard to the attribution of extremes, often we cannot say that these events were caused by global warming. In fact we're often asked that; is this due to global warming? It's not the right question because there is, I would say, always a global warming component to what is going on nowadays, but most of what is going on is the natural variability, the weather. And I mentioned before, you know, how large is this effect? And I suggested that maybe it's in the neighbourhood of 5% to 10%, and we can argue that that's the kind of number you get in an extended drought.

But I do think because we're breaking these records, that it's highly likely that these events would not have occurred without global warming. Just remember, this is the only planet we've got. Thank you very much.

Robyn Williams: Dr Kevin Trenberth at the University of New South Wales. He's head of climate analysis at the National Centre for Atmospheric Research in Boulder, Colorado. And there's a Catalyst special on that next Thursday at 8pm on ABC1, Taking Australia's Temperature, don't miss it.