揭开天气谜团（二）Solving our climate history puzzle（2）

亲爱的听众朋友们大家好！欢迎收听墨尔本大学官方音频节目。

我们的电台节目将为大家带来最新鲜有趣的，关于科学、文化等前沿英文原版节目。欢迎您持续关注！

揭开天气谜团（二）Solving our climate history puzzle（2）

Steve Grimwade 
Have to convince you though that Mountain Ash is as beautiful a tree and we'llsend you up to the Dandenongs. Not as long lived unfortunately.

Joelle Gergis 
Yeah.

Steve Grimwade 
Look and this is - I've got a love of trees so I've got to ask a little bitfurther. You write of polishing that sample because you core into the tree andyou bring out a sample which is quite thin. Is it one distinct piece and canyou polish the whole piece? Is it a foot long, is it two feet long?


Joelle Gergis 
Okay, good question. So basically what we do is we use a handheld incrementborer which is effectively like a large corkscrew and we hand-drill it into thetree. It doesn't damage the tree in any major way otherwise you wouldn't beable to do it. Then we extract a wooden core which is effectively the size of adrinking straw, it's really tiny. Then what we do is we mount it on a woodenblock and then we sand it down using sandpaper. What that does is actuallyreveal all these nice rings. You can either do - we had permits to look at 30cmcores but also metre cores from some of the older trees. So we were looking ata metre of just a really thin rod, if you like, of wood and usually we wouldtake three different samples from each tree to make sure we haven't skipped aring because sometimes if there's wedging it doesn't put down a ring in an evenway. You might miss it, so you have to do three different samples to be able toget an indication of the correct dating which is - it has to be as precise as possible.It's the most precise method we have in paleoclimatology and it basically formsthe backbone of what we understand about long-term climate variations in themost precise part of the geologic record.

Because you can use other thingslike ice cores and marine sediments which give us really long-term records. Butin terms of the year by year tree rings are the best records that we have. So Ihope that makes sense. So effectively what we do is we just have these sampleswhich we sand down and then we look at them under a microscope and then countthose different ring widths. So we were looking at that alternation betweenwide and narrow to get a sense of are there patterns. Then we pull all of thatinformation from an individual tree into all the different trees we've got froma stand of forest and then a whole bunch of study sites that we have. So in theend you can have hundreds of trees, 500 trees at times because like I said thisproject was part of a longer term study that's been going for about 20 years atthe University of Auckland. I was a PhD student working there.

Steve Grimwade 
So I guess we've now got to come to not the end of the story, it might be thestart of the story actually. What has the data shown you?

Joelle Gergis 
It's a good question. I'll talk about what we've found in terms of once we wereable to collate all these different types of records, so we collected theCowrie Tree rings from New Zealand and we also looked at Great Barrier Reefcorals and ice cores from Antarctica. I was involved in a global effort toconsolidate all of these natural archives for our region. Then what we wantedto do is figure out well what's the temperature been like in our region becauseobviously the globe is warming and we wanted to understand whether or not thetemperature we've been experiencing in our region is it unusual or is it justpart of these long-term natural fluctuations?

So what my team did is wedeveloped a 1000-year temperature reconstruction using all of these naturalrecords. Year by year, we went back year by year in time. What we found is thatthe warmest 30 years of the last 1000 years actually occurs in the most recentperiod, from 1985 to 2014 which was the last data point we had for theparticular study. Effectively what that shows is that we are now starting tomove out of the realm of natural variability that we've just seen in the recentgeologic past. Another part of that study was that we also looked at climatemodel simulations where we were able to determine well is this just a naturalfluctuation or is this something that has a human fingerprint? So we looked atthat and we found that we couldn't reproduce the rate and the magnitude of thewarming that we experience in our region without having the presence ofgreenhouse gases in the models, which effectively showed us that theAustralasian region is warming and our fingerprints are all over that signal.

Steve Grimwade 
So you write that Australia has one of the most spectacularly erratic climatesin the world. Is there anything normal about our weather ever and what can weexpect?

Joelle Gergis 
So Australia sits in the one of the great subtropical desert belts of theworld. So just below the tropics we have effectively an arid zone and that justhas to do with the way that the atmosphere circulates. So places like Australiaand Chile and South Africa there are desert belts. So that inherently gives usa dry climate. So we're actually a continent where two-thirds of Australia iseither arid or semi-arid. So we receive less than 50 cm of rainfall a year,which is not very much at all. So it's a very, very dry continent. 

Effectively we just have thesewet coastal fringes where most of our - 85 percent of our population lives onthe coast. So that gives us sort of the background in terms of the sort of setup that we're dealing with when it comes to climate variability in Australia.So the other issue or the other factor that drives Australian climatevariability is that we're a large island surrounded by ocean. So our climate isinfluenced by a range of different sources from the Indian Ocean, SouthernOcean and the Pacific Ocean. What that does is bring in a whole range offactors which makes it quite complex actually compared to some other differentregions of the world where they might just have continental area where theymight be far from the sea and it's a pretty moderate climate. But withAustralia because of our positioning on the planet in that sub-tropical regionof the world and also because we're surrounded by a lot of ocean, it means thatwe are in for an interesting ride sometimes.

Steve Grimwade 
If we have high variability is it hard to make that charge that it is actuallynot all natural variability?

Joelle Gergis 
Well this is where I think there's been a lot of public confusion because itseems that because we have this high variability that can sometimes mask theclimate change signal. So people think well we've all been through it allbefore but that's not quite the case. So we know that Australia is the land ofdrought and flooding rains. This we know, no one disputes that. 

But in recent years, reallysince 1850, around the world we've actually changed the chemistry of theatmosphere and the ocean to such a point where we've actually changed thefundamental operation of the climate system. That's been through the burning offossil fuels to support human activity and also the clearing of land surfaceswhich also alters the carbon cycle. So forests soak up CO2 and moderates thewarming that we experience around the world. 

So since 1850 we've actuallyaccelerated the rates of change that we've experienced and what that does is itmeans that all of our weather and climate is now occurring on the background ofa warming plant. So if you can think of it it's sort of like naturalvariability but on steroids. It's getting a bit of a kick from this warming andwhen you might think well Australia is warmer by one degree. But even with onedegree we're starting to see some very serious impacts and that's whyscientists are really concerned. 

Because if we are careering downthe line to a future world where we are very likely at this stage to cross overthe two degrees that is set out in the United Nations Paris Agreement in termsof trying to stabilise climate change, then we're looking at a radicallyaltered planet.

Steve Grimwade 
What were you most surprised by in your data? Was there anything in particularthat stood out and made you think twice or more than that?

Joelle Gergis 
Well I guess for me when I approach this question just from a scientific pointof view we didn't really know what we were going to find. The warming in theregion is really distinctive and you see it and it stands out. I guess it wasjust a surprise to see that. I mean you never know what you're going toexperience when you do scientific research but it was a very clear result and Ithought it's something significant when we had it and when we sort of ran thenumbers and looked at it, we realised that we had a significant piece of workon our hands. Because people had already looked at the instrumental record andlooked at those climate modelling studies and determined that there was a humansignal in the Australian climate record. But it was the first time we were ableto use those records from the natural world and also it was just another lineof evidence if you like. 

I guess what did surprise me noteven from the scientific perspective, it was more from the broader perspectiveor community or political perspective if you like, was the backlash that ourteam received as a result of that. That was probably the most surprisingelement, not the actual scientific results.

Steve Grimwade 
Yeah I guess scientists from the renaissance have often found themselves on theright end of history or science but the wrong end of the stick. How were youprepared for the controversy that came out of your research?

Joelle Gergis 
To be quite honest I don't think I really was prepared. As a scientist we justdo our work and then I guess naively put it out into the community in the hopethat it helps somehow.

Steve Grimwade 
Maybe we can actually explain what that controversy was?

Joelle Gergis 
Okay the controversy just had to do with that temperature reconstruction paperthat we looked at. I mean there's a chapter in my book which details some ofthe details around what actually happened, but effectively people were tryingto undermine the results and sort of discredit me and also my team and castdoubt on the results that we'd come up with in that study which was, yeah, itwas unfortunate.

Steve Grimwade 
How do you keep certain of your work when it's under sustained attack? Whatbecomes important to you in your life as a worker, as a researcher, as a human?

Joelle Gergis 
Yeah there's two parts to that question. The first is - how do we remainconfident? Well we ran our results 1000 times each using four differentmethods. Sorry, 3000 times each using four different methods. So in the end wehad 12,000 different reconstructions using the same data set. 

Then we used a separate climatemodel just to make sure that we had also not - you know that that result wasalso reproducible because in science things need to be reproducible. So if wereproduce the results using four different independent statistical methods andalso different climate models then we can probably say we're fairly confidentin our results and we were. That's why we persisted with this, because it wasimportant. Even though we were under a lot of pressure, an immense amount ofpressure, we felt that it was an important result for the region and weren'tgoing to back down.

Steve Grimwade 
Was there a piece of advice or support that you received in this period thatprobably helped more than any other? Or even during your life more generally?

Joelle Gergis 
I mean I was really lucky to have a terrific mentor, Professor David Karoly.He's a bit of a stalwart of climate change debates in Australia and I wasreally lucky to have his wisdom to draw on. He had a lot of great personaladvice but also legal advice because we were coming under legal attack throughthe Freedom of Information request avenue where we had to release a lot ofemails and people were poring over our correspondence and things like that. 

Look, I think it probably hit mehard. I don't think I was prepared for it. I mean thankfully I've got terrificsupport networks around me now. So I think if anything like that happened nowit'd be quite different.

Steve Grimwade 
If we can learn from you, I mean obviously you do science for an outcome and inthe hope that people will learn. That's, I mean, both big picture policy butthat's also individuals. I mean you wrote that research shows that between 1988and 1997 one farmer committed suicide every four days, and I think this was aresult of the drought at the time. So how is climate science and modellingbeginning to help farmers prepare for their world?

Joelle Gergis 
Well it's interesting. I've just literally this week been at a conference onclimate change adaptation and I saw a really interesting presentation by asenior economist actually at the University of Adelaide. She was looking atwhat actually causes a farmer to walk off their land. She looked at a wholerange of different variables but the number one factor was maximumtemperatures. So when conditions became too hot they had to walk off the land.It just became unviable to actually farm under those conditions, because if youthink about it I mean temperature also influences the amount of availablemoisture that's in the system. Whether it be through dams with evaporation andthat kind of thing, but effectively it's becoming too hot to farm in parts ofthe Murray Darling Basin. So people are walking off the land. 

She was also saying that that'shaving really big impacts because if you're thinking about somebody say intheir mid-60s walking off the land and maybe they're multiple generations ofpeople that have worked that land, they have an identity crisis and they don'tknow what to do with themselves. Many times that leads to a lot of mentalhealth issues and people become really despairing and despondent and it can endin personal tragedy.

更多节目欢迎关注墨尔本大学官方中文频道：

微博：墨尔本大学官微

微信：MelbUni1853

网址：www.unimelb.edu.au

本期节目网址：https://pursuit.unimelb.edu.au/podcasts/solving-our-climate-history-puzzle