Glen Paul: G'day, and welcome to CSIROpod, I'm Glen Paul. The State of the Climate 2012, recently released by CSIRO and the Australian Bureau of Meteorology, details the latest observations of Australia's climate, and provides analysis of the factors that influence it.
The headline finding in the State of the Climate 2012 is that Australia's land and oceans have continued to warm in response to rising CO2 emissions from the burning of fossil fuels. Though much of Australia has swung from drought to floods since the last State of the Climate summary in 2010, it notes that the long-term warming trend has not changed, with each decade having been warmer than the previous decade since the 1950s. And what's more, the rate of change is increasing.
Joining me on the line to discuss the State of the Climate 2012 is CSIRO's Dr Michael Raupach. Mike, what are the fundamental differences showing up in this summary compared to the observations made in 2010?
Dr Raupach: Well the first difference is that over the last two years there has been a cooling trend in Australia because of two significant La Niña events in the Pacific Ocean. The major issue that everybody wonders of course is whether this cooling trend is the start of something much bigger, that somehow global warming has ceased, or the alarm bells have been ringing much too loudly.
This by all objective analysis is not the case. The cooling trend over the last couple of years in Australia is no indication that global warming has ceased, and the main reason for that is that we can attribute the cooling trend pretty reliably to the two La Niña events in the Pacific Ocean, which have the consequence of pulling down temperatures globally. This is a well know feature of La Niñas, that correlate very well with mild temporary coolings in the global atmosphere and climate, and this is what’s caused the temporary drop in Australia's temperature.
So we do not think that the cooler temperatures over the last two years in Australia are a signal that in any sense global warming has stopped.
Glen Paul: So the rains and the ensuing floods haven’t muddied the waters, so to speak, in relation to what is climate change. But how do you separate weather patterns such as El Niño and La Niña from the effects of climate change?
Dr Raupach: That is done by distinguishing the short term from the long term, and we know that short term weather has always fluctuated on scales from days to years, we've had climate variability on all of those scales for as long as we’ve been able to record the weather, and historically of course anecdotes tell us that this has been around all the time throughout human civilisation and longer.
So we, in order to detect climate change, have to screen this kind of short term variability out of the longer term trends, and this can be done in a number of ways by applying various filters to the record to remove the influence of El Niños and La Niñas, and other causes of short term fluctuations, including volcanic eruptions.
And when this is done the longer term trends remain clear, they’ve been clear for a century or more in the record of observations that we have, so those longer term trends are one – by far from the only one – but one of a number of reasons why the climate community believes that climate change is a reality, that the major cause is anthropogenic human emissions of carbon dioxide and other greenhouse gases, and that longer term we need to bring those emissions down in order to prevent climate change from getting into really dangerous territory in the coming Century.
Glen Paul: Hmm. And how and when will climate change begin to impact on these weather patterns themselves?
Dr Raupach: Well there has of course been speculation that climate change is already impacting on weather patterns, that we’ve had the warmest sea surface temperatures on record off the north coast of Australia, this has been associated with very high rainfall events, particularly in the north, and to some extent on the eastern part of the country. So there’s some evidence beginning to emerge that there is a link between these high temperatures, certainly they can be attributed to the combined influence of La Niña and a general warming of the climate, and those high rainfall events in northern and eastern Australia.
Glen Paul: Uh-huh. Now according to the summary, concentrations of long lived greenhouse gases in the atmosphere reached a new high in 2011. What sort of increases are we seeing there?
Dr Raupach: Since 2000 we’ve seen an increase in greenhouse gas emissions, particularly the emissions of carbon dioxide, at around 3 per cent. per year. That has continued up to the last year, despite a small downward blip in 2009, associated with the global financial crisis. That blip was completely overcome the following year, 2010, where the rate of increase of carbon dioxide with emissions from fossil fuels was about 5.9 per cent.
So we've seen through the last decade fossil fuel emissions of CO2 increasing at about 3% per year on average. That’s translated to a rise in CO2 concentrations which on average through that decade, the last decade, has been close to two parts per million per year; last year it was indeed two parts per million per year. And the consequence of that is that we’ve seen an increase over the last Century in CO2 concentrations from preindustrial values of around 280 parts per million, to the current value which is now well above 390 parts per million.
I checked the other day the reading from the Mauna Loa, CO2 observations in the reading for December 2011 was 393 parts per million for CO2. So we are indeed seeing this long term trend, very steady, despite the inter-annual variability and the strength of the CO2 sinks in land and ocean, that’s causing CO2 concentrations to rise at the moment by about two parts per million per year.
Glen Paul: Hmm, and of course with the rise in CO2 emissions comes the further warming of the land and the oceans. Does sea level rise continue to be an issue in the report?
Dr Raupach: The sea level rise does continue to be an issue. It’s been going up globally by an average of about just over three millimetres per year for the last three decades. Sea level rises around Australia are not uniform, and the sea level does not go up like water in a still bath which is having a slow tap run into it; it doesn’t rise uniformly all around the world. Sea levels vary, and the rates of rise vary from place to place.
Australia, for reasons associated with ocean circulations and wind patterns on the oceans, has seen larger rises around its coastlines on average than the rest of the world. But the major story is that we can expect to see sea level rise continuing, and most of that sea level rise is because of thermal expansion of the oceans – that is the ocean waters expanding as the climate warms.
Ninety percent of the excess energy that the earth’s system is receiving as a result of excess greenhouse gases in the atmosphere ends up in the oceans, and that excess energy is responsible for the bulk of the sea level rise that we’re seeing.
Glen Paul: OK. Now, much of Australia's population is concentrated along the coast, and some might say, well they’ve not noticed any significant change in sea level down at the local wharf, where they’ve fished for years. When might they start to notice or what might that wharf look like in 50 years time if things continue the way they're going?
Dr Raupach: Well, if sea level rise continues as predicted we’ll be getting rises of anywhere between 30 centimetres and well over a metre, with a median prediction of well over half a metre by the end of this Century, by 2100. So if half of that was realised by 2050, then we’d be looking at sea levels which are anywhere between 15 and 50 to 60, or even higher, centimetres above where they are now on the median.
Of course, this will cause a difference to sea levels of wharves, but perhaps more importantly it will cause increased damage as a result of storm events, because the relationship between inland propagation of a storm and sea level is highly leveraged. Storms will come in a lot further inland as a result of storm surges and the like, in response to each metre of sea level rise by something like a factor of one to a hundred.
Glen Paul: And obviously that’s not the kind of news that we want to hear about our future, yet you don’t come to these conclusions by pulling facts and figures out of your hat, to put it politely. A lot of work and top notch science goes into these reports. How does it make you feel when you hear some commentators being so dismissive of the research?
Dr Raupach: There is a tremendous tendency in the public debate about climate change to have that debate revolve around factoids, around small pieces of information which are taken out of context, and one example is the claim by some commentators that for Australia to meet its emissions reductions target of 5 per cent below 2000 levels by the year 2020 would make zero difference, or negligible difference to global climate change, on the grounds that Australia contributes only 1.3 per cent of global emissions anyway.
This ignores the fact the atmosphere is a globally shared commons, and climate change is a global problem, and therefore for Australia to take a stance like that would be inviting the view that Australia is not serious about climate change at all. Or we could draw the analogy between a speeder on a road who argues that he can drive perfectly safely, and therefore speed limits should not apply to him, and our society takes a dim view of that kind of thing.
And it’s likely in coming years that the global society will take a dim view of nations which take the corresponding view of the global atmosphere, that is that to the extent that climate change is perceived as a global problem, it’s everybody else's problem, not our own.
So we, Australia, need to meet our emissions targets, not only because we will make a difference – we will – but also because it’s the only way of us showing that we expect other countries to do the same thing.
Glen Paul: Fair enough. And of course people are welcome to form their own opinions by reading the summary, which is available as a downloadable PDF on the CSIRO website. Thank you very much for talking to me today about it, Mike.
Dr Raupach: Thanks, Glen.
Glen Paul: Dr Michael Raupach. For more information find us online at www.csiro.au. You can like us on Facebook, or follow us on Twitter at CSIROnews.
