揭开天气谜团（一）Solving our climate history puzzle（1）

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（一）Solving our climate history puzzle（1）

Chris Hatzis 
Eavesdrop on Experts, a podcast about stories of inspiration and insights. It’swhere expert types obsess, confess and profess. I’m Chris Hatzis, let’seavesdrop on experts changing the world - one lecture, one experiment, oneinterview at a time.

We’re all aware of the very realproblem of climate change in the present day, but what was Australia’s climatelike before official weather records began? How do scientists use tree-rings,ice cores and tropical corals to retrace the past? What do Indigenous seasonalcalendars reveal? And what do colonists’ diary entries about rainfall,droughts, bushfires and snowfalls tell us about natural climate cycles?

Dr Joelle Gergis is a climatescientist and paleo-climatologist at the University of Melbourne. She's a writerand stitcher of climate time, bringing together these bureau recordings,colonists' diaries, Aboriginal dreaming stories and tree rings. Her book“Sunburnt Country” pieces together Australia’s climate history for the firsttime, and uncovers a continent long vulnerable to climate extremes andvariability. Dr Joelle Gergis sat down to chat with our reporter Steve Grimwadeabout her book, her work in deciphering Australia’s climate story, and whatclimate change looks like in our own backyard.

Steve Grimwade 
Joelle, thanks for joining us.


Joelle Gergis 
My pleasure.

Steve Grimwade 
Let's go back to when it all started. What was your first memory of science?

Joelle Gergis 
Well I guess my first memory more of, I guess, climate extremes would be in1994 as a high school student. I was living in Sydney and there was reallymajor bushfires in my local area and there was just ash falling all over ourneighbourhood and it was really quite terrifying. It made me start to think alittle bit about climate extremes. Then later on when I started university Ilearnt about El Nino which is one of the main drivers of Australia's climatevariability. I learnt that these things were quite related. 

So I started to want to be ableto join the dots between the sorts of things that we experience as humans,things like bush fires or droughts or floods or various other extremes and tryand join the dots of what causes them and are they changing.

Steve Grimwade 
2009 or thereabouts you started a project that seems to have consumed much ofyour life since then. What was it and what was the objective?

Joelle Gergis 
Okay, so it was called the South Eastern Australian Recent Climate HistoryProject or the SEARCH Project. It's a little bit of a mouthful.

Steve Grimwade 
Great acronym though.

Joelle Gergis 
Yeah, so effectively what it was trying to do was reconstruct our climatehistory back all the way to 1788, where we had first European settlement in thefirst instance. So we wanted to really get a sense of what records we could usefrom the colonial era. So things like early settler accounts, early newspapers,government correspondence, even farm diaries and things like that. So there wasa whole range of different historical sources that had been really overlookedwhen it came to weather and climate variability. So we teamed up with theNational Library, the State Library of Victoria, the State Library of New SouthWales and also historians here at the University of Melbourne. We tried topiece together what the historical record had to say about past climateextremes and just general variability which was really interesting and excitingas a scientist to be able to delve into these really rich resources that we asscientists don't often get to do.

Steve Grimwade 
It's an interesting idea too because I'm interested in how well has humanmemory served us with regards to the variability of climate and actuallyrecording these changes. How much can you trust a colonist, and there's one inparticular I think in 1788 that says from the boat “I can see snow”. How canyou trust that?

Joelle Gergis 
Well, that's a really good question. So that's why we'd never really look atone sort of data source in isolation. So we looked at these diaries andanecdotal accounts from historical record but we're also really interested inrecovering early weather records. So there are actually instrumental weatherobservations of temperature and air pressure and sometimes even rainfall thatwere actually contained in a range of different scientific sources. So not onlywould we look at the diaries and what people were saying that were actuallyexperiencing these weather and climate extremes in the landscape, we alsolooked to cross check to see whether or not they were just being, you know,exaggerating a little or something like that. 

So always in the type of workthat I've been involved in in the past decade we always try and use multiplelines of evidence. So aside from looking at those early historical records, welooked at early weather records which are quantitative numbers if you like, andthen we also used records from the natural world. So we looked at things liketree rings and corals and ice cores from the broader Australian region to beable to take our understanding of climate variations back centuries into thepast. 

So we kind of used a bit of athree-pronged approach to the exercise which I think was pretty useful. Anothersource we looked at was climate models as well, because in some of the workthat we looked at we wanted to understand well is it just natural variabilityor are we actually looking at a climate change signal which has got to do witha human fingerprint on the Earth's climate?

Steve Grimwade 
You've recently released a book “Sunburnt Country”, released by Melbourne UniPublishing and I'm going to return to this later on on how you approached thewriting. But an interesting aspect of this are the paintings and the picturesand the art that is another resource for actually finding out what happened.Can you tell us about that?


Joelle Gergis 
Yeah, that was one of the most enjoyable aspects I think of writing this bookand also doing the research is that we were really lucky to have partners likethe National Library and the State Libraries and often they would send usimages. 

So they knew we were looking atthings like droughts and floods and bushfires and it was amazing to see thatactually in the historical record in the pictures collections that there werevery often just like I guess today when there's a significant weather event,people like take photos of them or they record them. But in the early era theydid watercolour paintings and other types of artworks. Then in the 19th centurywhen photography was available there's also a range of really early historicalimages. So once we had an image we could also have a look to think about whatwas the story behind that particular event and that was really interestingbecause I think it is a nice way of just engaging in this topic in a reallydifferent way. I really like art and I think it was just a nice way to bring itto life because it's not just always about the numbers.

Steve Grimwade 
So when we try and work our way backwards and we do try and work our way fromthe current bureau recordings and then we go further back and we go to thediaries and we go to those first instrumental recordings. Then you go backthrough - well, you go through dreaming stories as well. Maybe can you tell meabout how Indigenous stories, have they informed this research? Can they?

Joelle Gergis 
So, a lot of people are really interested in Indigenous stories and for goodreason, they are really fascinating. I guess it's not exactly the kind ofinformation that we can directly use in the type of work that we do, becauseoftentimes we are looking at quantitative measures of say temperature orrainfall and these sorts of climate variables. So that's not to say it's notuseful information but it's a little bit yeah, not quite direct. 

But what it does do is itprovides us with a lot of really interesting information about how Indigenouspeople were perceiving the landscape and the climate over long periods of time.Even right now, so for instance the Bureau of Meteorology have actually donesome work with Indigenous communities in various places that have found thatthere are up to six different seasons recorded in different parts of Australia.So that really is a little bit different to the European sort of four seasoncalendar and so that gives us a really different appreciation and this sort ofnuance about the landscape. 

So Indigenous people werelooking at things like the timing of flowering plants or the arrival ofparticular water birds and changes in wind direction and rain clouds and thingslike that. So they're really interesting stories and I do talk about them in“Sunburnt Country”. But in terms of the research it wasn't actuallyincorporated in the main part of the project. But I did want to look at it sothat's why I put it in the book.

Steve Grimwade 
Let's go back beyond the dreaming stories to tree rings, core samples. I meanthis really is where your work begins to sort of capture us and really it seemsto be the foundation of your work is stitching together different ways ofunderstanding geological time or climate time.

Joelle Gergis 
So our understanding of climate variations is really confined to about 150years where we've got instrumental weather observations around the planet.While that is really interesting and important and it's definitely the highestquality record that we have, to be able to go further back in time to look atthese longer-term cycles that are present in the Earth's climate we have tolook at other records. So we look to the natural world. 

So when we've got things liketrees, they put on an annual band and that annual ring is related to thingslike temperature and rainfall variations during its growing season. So whenit's a poor year it might put on a very thin ring and when it's a really goodyear it might put on a wide ring. Then you can actually determine a statisticalrelationship between the instrumental weather observations that you have fromsay the Bureau of Meteorology. You can look at the period of overlap with thetree ring record and then you can develop that statistical relationship andtake that back in time. So effectively you end up extending the climate recordby hundreds and even thousands of years in some instances. So we use that ideaand that field of science is known as paleoclimatology and paleo just meansancient and climatology is all of accumulated weather. So what we're able to dois provide us with that long lens view, that long-term perspective on what theclimate was doing before we actually had people recording weather observationsand the landscape.

Steve Grimwade 
So we have Huon pines in Tasmania we say they get us back maybe 700 or 800years perhaps do they or…

Joelle Gergis 
Even longer. Some of those - the longest tree I think - the oldest tree inTasmania I think is around about 2000 years at least. That record from the HuonPine is about 4000 years old.

Steve Grimwade 
Terrific. Because you can also - you can probably dredge up old Huon pines thathave been long dead.

Joelle Gergis 
That's right exactly. So once a big old tree dies and gets covered up in aswamp or something like that, you can actually recover that material and thenpeople look at that and they're able to piece together the tree ring recordfrom using modern trees which are still alive and in the landscape and alsodead trees that are buried. So you have these buried forests that people lookat and then you can actually stitch all of that together and get a reallylong-term climate record. 

So I think the Huon Pine recordthese days is around 4000 years old, 4000 years in length which is quiteremarkable. It's one of the longest in the Southern Hemisphere for sure. So wedid use that record when we were looking at this work and we also used materialfrom New Zealand. In Northern New Zealand there's a species called Cowrie whichis part of the Agathis group which is a really ancient conifer. It's alsorelated to the Wollemi Pine group that's in the Blue Mountains that some peoplemight have heard of. So these are really ancient trees from a time when theEarth was really young and so they're really rare and there's not too many ofthem left. Luckily, we were able to access some of those forests in NorthernNew Zealand and use that type of work for climate reconstruction.

Steve Grimwade 
My view of you as a researcher, and researchers more general, is this idea ofdry science. But really when you write the story about going close to TaneMahuta which is in - is it the Northlands of New Zealand or…


Joelle Gergis 
Yeah, Northland, yeah.

Steve Grimwade 
Yeah, yeah. But you get the opportunity to go sort of to other trees that aredeeper in the forest that punters like myself can't see and you also describe areally beautiful experience with the local Indigenous people and theirrelationship with the tree. Maybe you could talk about that.

Joelle Gergis 
It really was a privilege working in that part of the world. I was part of aresearch team that had been working on Cowrie tree ring science for about 20years and we obtained special permission to go and sample these trees. Weexplained why it was important and it actually took me about six months ofcommunity consultation where I went and spoke to community elders and I spoketo a range of different groups and I explained what we were doing and why itwas important. 

Once they understood that theywere really behind it and we actually had some local guys come and help us out.We had an elder come as well and bless our work in the forest which was reallyquite extraordinary. Really, to be walking through these really ancient forestsand these forests giants it's one of the most special experiences I think I'vehad in my life and I doubt I'll ever get to do something like that again.

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