Stories of Change Project

Camille Parmesan interview

Key

RH:      = Roger Harrabin, Interviewer

CP:      = Camille Parmesan, Professor, Oceans and Climate Change, Participant

RH:         OK Camille Parmesan,  can you start with telling me how we’ve underestimated things?

CP:         Well, in past reports, past IPCC reports and the big event analyses that have been in the scientific literature, there have always been some species that have been showing no change and that can be up to 30 or 40% of species in a study.

RH:         OK. So tell me what you’ve found which is new?

CP:         So with the warming that we’ve had what we expected and what we’ve generally found is that most species are responding by either changing where they live, by shifting poleward or up the mountains or changing the timing of spring events, so they’re breeding early, emerging earlier, migrating earlier. But in every study there’s always a certain percentage of species, it could be as little as 20% or as much as 40%, that aren’t changing, even though they're in an area that’s warming and even though other species in the same area are changing. And we’ve never really known what this meant, does it mean that they aren’t sensitive to climate change or does it mean that something else is going on that’s countering climate change that we don’t understand? So this is –

RH:         Well that would’ve been good news if the latter were the case.

CP:         Yes, it would’ve been good news. And so it’s been something I’ve always been curious about and just recently I’ve been starting to do more sophisticated analysis to try to explore what’s really happening with those species that appear not to be responding to climate change.

RH:         And what is happening?

CP:         So what we did is we took a very large UK dataset, long-term dataset, 46 years on flowering plants, and what we looked at was not just were they responding to spring temperatures, which is sort of the simple analysis that most people do, but we looked at how they might’ve been responding to temperatures throughout the current spring plus the whole year-and-half before. And once you do that you find that, alright, three-quarters of species only respond to spring temperature, they respond by advancing their flowering, that’s what we see, that’s what has been driving that major global signal of response to climate change.

RH:         And that’s well established, we kind of know all that, spring is getting earlier.

CP:         Yeah, it’s very well established and quite frankly it’s old news. But what’s exciting is that 20% of the species were not showing any change over that 46 years and yet when we looked at their sensitivity to temperature we found that they’re very sensitive to temperatures, just in a much more complex way than what we expected. So they respond to spring warming by advancing, but they respond to warm winters by delaying flowering

RH:         Why would they delay flowering because of a warm winter?

CP:         So that sounds very odd until you look into the plant physiology literature and you find out that a lot of these northern species, such as would be in the UK, need winter chilling. So a cold winter gives them the cue that winter is happening and as it warms up in spring it tells them, OK, winter’s over, now it’s spring, now I can start flowering. But when you have a warm winter they keep waiting around for the cold because they keep thinking winter hasn’t come. And so that waiting around causes them to delay flowering. Eventually they give up and they will flower, but it often comes out over this 46-year period as an actual delay in flowering which is a response to warming winter. And if they’re ones that also respond to warming spring by advancing, the observations are the combination of these two opposing forces for these poor plants, you know, warming spring is driving them to advance but warming winter is driving them to delay. And so many, many of them, most of them actually end up not showing any change in their flowering at all over this almost 50-year period, even though they’re very sensitive to the changes in temperature that anthropogenic climate changes have brought about.

RH:         I could imagine a climate sceptic’s response to this which is, look, here’s these biologists, they can see climate change in a lot of species but there’s others that appear to be not responding to climate change, so now they’ve come up with this fanciful idea that the fact they are not responding means they actually are responding.

CP:         The key is it’s not an idea, it’s actual data and that’s the whole point and that’s the reason why we worked with this UK dataset, is it’s very long-term. So we found out that you actually do need about 50 years of data because you need combinations of cold winters, warm springs, warm winters, cold springs in order to tease apart the differences in response between winter temperatures and spring temperatures and with this long-term dataset we were able to do that. And you can see over these many, many years that if you have a cold winter and you have a warm spring flowering is very early; if you have a warm winter and a cold spring flowering is delayed; if both of them have warmed, if you have warm winter, warm spring you tend to get no change at all in that year. So if it were just an idea I might agree with them but it’s not an idea, it’s very much based on very strong results from statistical analysis of very good long term datasets.

RH:         Can you give an example of any specific plants?

CP:         Well, in Britain what we’ve found is that there’s a whole set of plants that only respond to spring, such as the field maple, warmer spring it advances its flowering, very simple. But there is another group of plants, about 20% of them that need winter chilling and when they don’t get it they sort of hang around waiting for it and delay their flowering.

RH:         So that’s if it’s been a warm winter?

CP:         If it’s been a warm winter. If it’s a cold winter they actually do respond, just like everything else, to a warm spring by advancing flowering. So old man’s beard, the clematis that’s in the UK is in this category, it responds to both winter and spring warming but in opposite ways. And so what we see over the 46-year period is actually no change in its flowering date, even though it’s incredibly sensitive to temperature changes in winter and in spring.

RH:         So what happens if you were old man’s beard and it’s a warm winter then what’s going on in your head? Let’s suppose it would have a head under your beard.

CP:         <Chuckles> Well for old man’s beard what it’s wanting is a really cold winter to give it that cue to re-set its clock to say, OK, winter’s here and then when spring starts up as it warms it knows it should start flowering, but when winter is too warm it keeps hanging around waiting for that cold snap, eventually it’ll give up and it will flower –

RH:         So even if there’s a warm spring it’s not prompted to flower?

CP:         That’s right, the spring temperatures are driving the flowering in the opposite direction from the winter temperatures, so the overall observation over the 46 years is the combination of these two opposing drivers. So when you’ve got warm winters and warm springs the warming winter is causing them to delay, they’re waiting around for it to be cold, the warming spring is kind of still driving, eventually that kicks in and they realise it’s too warm and they start advancing their flowering, but when you get those two together they basically equal each other and what you see is no change at all in flowering date.

               In this study most of the species that were showing no overall change over that 50-year period actually were very sensitive to climate change, just in ways that were much more complicated than we expected. So we underestimated the proportion of species that actually have been impacted by recent climate change. That simple analysis where you look only at spring temperature, we estimated about three-quarters of species were impacted by climate change, but in this new analysis that includes winter temperatures we find that 90% of the plants in the UK were actually sensitive to recent climate change.

RH:         Is this published or will be published or it’s been published already?

CP:         This is published in PNAS in 2012, yes.

RH:         OK, Brilliant. Thank you very much.

<End of Interview>

• The Sustainable Earth Institute main website, Plymouth University
• The Sustainable Earth Institute Blog, Plymouth University
• Marine Institute, Plymouth University      
• Environmental Science Institute, University of Texas at Austin
• What We Know, a science outreach project of AAAS (the American Association for the Advancement of Science)
• Carbon Brief      
• Climate Communications, Aspen Global Change Institute

• video lecture: "Biodiversity and Climate Change", Linnean Society Lecture, Camille Parmesan
• ACCESS news interview, Camille Parmesan (presented in sign language)
• video: "Global Warming: Impacts on Wildlife and Society," University of Texas Environmental Science Institute, Camille Parmesan
• video interview: "So You've Got Climate Change: Living In A Warmer World - Part 1: A Chronic Condition," Texas Impact, Camille Parmesan
• video interview: "So You've Got Climate Change: Living In A Warmer World - Part 2: Small Changes, Big Impacts," Texas Impact, Camille Parmesan
• video interview: "So You've Got Climate Change: Living In A Warmer World - Part 3: Local and Global Action," Texas Impact, Camille Parmesan
• video interview: "So You've Got Climate Change: Living In A Warmer World - Part 4: Climate Change Tipping Points," Texas Impact, Camille Parmesan
• video interview: "So You've Got Climate Change: Living In A Warmer World - Part 5: Know Your Sources," Texas Impact, Camille Parmesan
• video interview: "So You've Got Climate Change: Living In A Warmer World - Part 6: Preserving Biodiversity," Texas Impact, Camille Parmesan
• webinar: "Living in a Warmer World", Texas Impact 7 min lecture, Camille Parmesan