The Australian Science Media Centre rounded up questions on climate science from journalists and put them to leading scientists in the field. Below is the resulting Q&A.
1) There has been conflicting messages about warming in recent years – is it or is it not getting warmer?
Professor Steven Sherwood, Climate Change Research Centre at the University of New South Wales
“The trend on meaningful time-scales has remained upward. Recent observations remain consistent with mainstream models and theories that predict warming. A longer period of sustained flat or cooling temperatures would be needed to challenge them.”
Associate Professor Kevin Walsh, Associate Professor of meteorology in the School of Earth Sciences at the University of Melbourne
“It is getting warmer, but not at the same rate everywhere. Take the global average temperature, for instance. The year 1998 was the warmest year to date (because it was a big El Nino year), and if a trend line is calculated starting at 1998 going to 2009, this trend is not statistically significant. But if you take the same trend from 1997 or 1999, the upward temperature trend is statistically significant. And if you take a trend from 1900 to 2009, the upward temperature trend is REALLY statistically significant.”
“Why do I pick 1998? Because it is often said that the lack of a trend since 1998 invalidates the global warming hypothesis. But global warming is a trend superimposed upon natural variability, variability that still exists despite global warming. This means every so often you would expect a spike in the global average arising from natural variability alone, just like the year 1998. It would be MUCH more surprising if the global average temperature just kept on going up, year after year, without some years of slightly cooler temperatures.”
Professor Neville Nicholls, Professorial Fellow in the School of Geography and Environmental Science at Monash University
“The graph below shows global temperatures of the lower atmosphere (just above the Earth’s surface) averaged over November-January each year (ending in November 2009 – January 2010). The data are from Dr Roy Spencer and Dr John Christy (http://vortex.nsstc.uah.edu/data/msu/t2lt/uahncdc.lt), whose data have been used in the past to suggest that warming has ‘stopped’. As the figure shows, global warming is going strong, despite rumours of its demise. Global temperatures have increased about 0.5C since 1979/80 (satellite data started in 1979). Other data (temperatures over land, sea surface temperatures) show similar warming.”
Dr Paul Beggs, Senior Lecturer in the Division of Environmental and Life Sciences at Macquarie University, NSW
“The message from climate change experts about warming in recent years has been clear and consistent. Warming of the climate system is unequivocal. It is getting warmer.”
1) Is the warming of recent years statistically significant compared to other periods of inter-glacial warming? Are we simply seeing a blip, which will be smoothed out to something approaching normal inter-glacial periods or is this the start of something big?
Professor Steven Sherwood, Climate Change Research Centre at the University of New South Wales
“Most studies find that the warming stands out statistically, though this will be contested. What is more important is that the warming was predicted decades ago based on physical principles, and the predictions came true. The predicted future warming is much larger, if emissions continue. We ain’t seen nothing yet.”
2) Some sceptics say there is no evidence of a link between increasing carbon in the atmosphere, and increasing temperatures. Is the link clear?
Professor Steven Sherwood, Climate Change Research Centre at the University of New South Wales
“Yes, satellites can measure the greenhouse effect and its increase over time. These claims are false.”
Associate Professor Kevin Walsh, Associate Professor of meteorology in the School of Earth Sciences at the University of Melbourne
“If there is no link between increased concentrations of carbon dioxide in the atmosphere and global warming, then we don’t understand physics that has been used successfully in other scientific fields since the nineteenth century. There has to be a link. The controversy is about the size of the effect, not whether it exists or not.”
Professor Neville Nicholls, Professorial Fellow in the School of Geography and Environmental Science at Monash University, Melbourne
“Confidence in the reality of the link between carbon dioxide in the atmosphere and warming comes from three sources:
1. Laboratory experiments 150 years ago (and repeated many times since – you can even see a demonstration on YouTube) show that carbon dioxide is a greenhouse gas and that increasing its concentration will lead to warming unless other processes (a weakening sun, or massive volcanoes, or dust from an asteroid hitting the earth) offset this warming.
2. Predictions of the amount of warming expected from the likely increases in carbon dioxide have been made since at least 1959 (the 1959 prediction was published in Scientific American at the time). These predictions were initially done without the use of climate models, and were just based on physics. By the early 1970s, warming (up to the end of the 20th century) was being accurately predicted in journals such as Nature, using the climate models available at that time. Better models were used in 1988 to make predictions of warming, again proving quite accurate. Successful prediction is the standard technique that scientists use to confirm their understanding of a process. The success of repeated predictions (made over 50 years) of warming confirm our understanding of the physics of the greenhouse effect.
3. In recent decades, a large number of more sophisticated climate models that take account of a wider range of climate mechanisms, and do a better job of simulating atmospheric behaviour, have been shown to reproduce the observed 20th century warming and cooling episodes when they use anthropogenic influences (including greenhouse gas increases) but cannot reproduce the observed temperature behaviour if only natural processes (solar variations and volcanoes) are included in the model. Some of the variations in the Earth’s climate in previous ages were caused by changes in the amount of energy received from the Sun. But satellite observations show that there has not been a trend to more heating from the Sun over recent decades, so the Sun has not caused the warming of the past 50 years.”
Dr Paul Beggs, Senior Lecturer in the Division of Environmental and Life Sciences at Macquarie University, NSW
“The sceptics are wrong. There is considerable evidence of a link between the observed increase in anthropogenic greenhouse gas concentrations in the atmosphere and the observed increase in global average temperatures. The link is clear.”
3) With the recent attacks on the IPCC reports, can we trust the science and the scientists? Can peer review be trusted?
Professor Steven Sherwood, Climate Change Research Centre at the University of New South Wales
“This event has been horribly overblown. The unfounded claims that have caused the controversy were so minor, they were not even mentioned in the report’s Executive Summary. The executive summaries are vetted very very thoroughly, could not have errors of this kind, and contain all the findings of importance to policymakers. The bowels of the text, where errors have been found, are not vetted very well (especially in the WG II and III reports) and IPCC needs to address this.
It is worth pointing out that the sin of the IPCC–publishing a prediction with no scientific foundation–is one that contrarians do every time they say we have nothing to worry about.”
Associate Professor Kevin Walsh, Associate Professor of Meteorology in the School of Earth Sciences at the University of Melbourne
“I’m assuming that most will understand the process of peer review, but maybe not, so I’ll just briefly describe it. A “peer” is someone who is an expert in the field of the work being evaluated, or who is an expert in a closely related scientific field. Often, they will be scientific competitors of the scientists whose work is being evaluated. Sometimes, the reviewer may be deeply sceptical about the topic of the work being assessed. So peer review is certainly not a self-congratulation society of like-minded scientists. On the other hand, though, even rigorous peer review can let things slip through, or assess work incompletely. It’s not surprising, therefore, that in the several thousand pages of the IPCC reports, a few problems have been found with the review process.
“Can peer review be trusted? I guess the next question is what is the alternative? Review by non-peers, or in other words by non-experts? This does not seem like a viable alternative. There will always be some issues with any review process. But peer review is the best process that we have come up with so far to perform quality control on scientific publications.”
Professor Neville Nicholls, Professorial Fellow in the School of Geography and Environmental Science at Monash University, Melbourne
“In 2009 there were 7,541 peer-reviewed scientific papers published in the peer-reviewed literature with the topic of ‘global warming’ or ‘greenhouse effect’ or ‘climate change’. With such a large number of papers there must be some that are incorrect. But the large number indicates that this is a very busy field, and such a busy field should ensure that most of the work published is checked by many other scientists.
“All those journal papers have been reviewed by 2-3 other scientists, prior to their publication. The IPCC then assesses this mountain of published scientific literature. The Fourth Assessment cites over 10,000 papers from the scientific literature, most of which have already been through the peer-review process to get into the scientific literature. The IPCC reports themselves are subjected to four reviews, over a 2-3 year period. The IPCC Fourth Assessment received about 90,000 comments from about 2,500 reviewers. The review comments are publicly available, as are the responses of the authors. So, any errors made by the authors in response to the reviewer comments should be found pretty quickly. It is hard to conceive of a more comprehensive and transparent process than that used by the IPCC.
“Once the IPCC reports themselves are completed, there is another process of review to prepare and revise summaries of the reports. Every sentence in these summaries is discussed and argued about (and finally agreed by consensus – not a vote) by scientists and representatives from more than 130 governments (and many of these government representatives are also scientists). It is hard to imagine any process of assessing a complex subject that would be subject to more comprehensive debate and review.”
Dr Paul Beggs, Senior Lecturer in the Division of Environmental and Life Sciences at Macquarie University, NSW
“Peer review can certainly be trusted, particularly the IPCC peer review process which is arguably the most rigorous and transparent peer review process in the history of science. Similarly, of course we can trust the science and scientists. Asking if we can trust the science and the scientists is like asking if we can trust medicine and the doctors. Just like we consult a doctor when we are unwell, we must trust and accept the consensus of the world’s climate change experts as clearly presented in the IPCC’s most recent Assessment Report (published in 2007, the year it was jointly awarded the Nobel Peace Prize with Al Gore).”
4) My sense is that earth’s carbon cycle is very poorly understood, the link between atmospheric, marine and terrestrial sinks. Much focus has been on the atmosphere – but is the real carbon action is in the world’s oceans?
Professor Steven Sherwood, Climate Change Research Centre at the University of New South Wales
“If I began pumping carbon monoxide into your office, and an alarm soon went off indicating CO levels were rising toward dangerous levels, would you dismiss concerns on the basis that there is much more CO in the global atmosphere than in your office and that you don’t fully understand the building’s air handling system?
“This is a slight of hand to distract the public from the clear facts that carbon dioxide rises are unequivocally due to fossil fuel burning (plus a few smaller sources). It sounds inspired by Ian Plimer’s book. His arguments rest on false assertions (which he continues to refuse to recant) and a willingness to ignore the most crucial evidence and arguments. His assertion that we don’t know why CO2 levels are rising or that is natural is preposterous and easily disproved.”
5) The sceptics say rainfall has not reduced in the Murray Darling Basin. What is the true story and how strong is the link with climate change?
Professor Steven Sherwood, Climate Change Research Centre at the University of New South Wales
“The sceptics here are (for once) technically correct, in that there is no proven link–yet– between Murray-Darling drought and climate change. BUT…(a) there are good reasons to expect most of Australia to gradually dry due to warming, regardless of any particular drought happening right now; (b) the severe droughts in southern Victoria and southwest Australia have been more firmly attributed to global warming; and (c) temperatures everywhere, including the Murray-Darling, are rising which increases the need for rainfall. Thus drought is worsening even though rain isn’t decreasing (because it isn’t increasing enough).”
Professor Neville Nicholls, Professorial Fellow in the School of Geography and Environmental Science at Monash University, Melbourne
“Annual MDB rainfall in each of the last nine years has been below 500mm (you can find these data at the Bureau of Meteorology’s web page). Prior to this dry period, the longest run of years below 500mm, since we have had decent data (starting in 1900), was six years (1925-1930). So, the current dry period is 50% longer than the previous record dry period. But this current dry period might still be just a fluke, or natural variability. We cannot confidently attribute it to global warming.”
6) What is the link between extreme weather and climate change? Sceptics say the link is weak and unproven.
Professor Steven Sherwood, Climate Change Research Centre at the University of New South Wales
“For some extremes this is true, but there is little doubt that a warmer climate will bring more extreme heat waves, and heavier downpours in areas that still receive ample rain. These things are being observed. We also expect more frequent and severe droughts, which is also being observed.”
Associate Professor Kevin Walsh, Associate Professor of meteorology in the School of Earth Sciences at the University of Melbourne
“The link is weak, but not necessarily unproven. I say it is weak because, so far, there is little indication of detectable trends in extreme weather events that can be tied directly to the warming that has occurred to date. One exception, of course, is increases in extreme high temperatures, which have been demonstrated in some regions of the globe to be associated with climate change trends. But for other phenomena such as tropical cyclones, trends have not been unambiguously associated with global warming. On the other hand, climate predictions suggest that we should start to see trends in some of these other phenomena, but probably not until later this century.”
Professor Neville Nicholls, Professorial Fellow in the School of Geography and Environmental Science at Monash University, Melbourne
“Hot extremes (hot days and nights, and heat waves) over much of the world have increased as the world has warmed over the past 50 years, while cold events (cold days, cold nights) have decreased in frequency and intensity. The link between these changes in extremes and global warming is very clear. Linking global warming and other types of extremes is more complicated. Some extremes (tornadoes, strong winds) are not monitored well enough to determine if they are changing. Some (tropical cyclones) are not modeled sufficiently well to make confident predictions of changes, or to understand the causes of changes. Some extremes (droughts, heavy rains) have been changing in different ways in different regions, so it is hard to make a global assessment. All the above issues are discussed in the IPCC Fourth Assessment reports.”
7) With so much uncertainty, what can we be sure about? There must be unknowns/missing links/things science is not so sure about. What are they?
Professor Steven Sherwood, Climate Change Research Centre at the University of New South Wales
“Relatively few things are certain, but these things should compel people to action. They are: (a) human activities (mainly fossil fuel burning) are increasing greenhouse gas levels, (b) increased greenhouse gas levels have a warming effect, and (c) we are observing warming at the rate calculated from this effect. None of this is contestable.”
Associate Professor Kevin Walsh, Associate Professor of meteorology in the School of Earth Sciences at the University of Melbourne
“If we wait until we have absolute certainty on all aspects of this topic before acting, we will never act. People in their daily and professional lives make decisions all the time without being absolutely certain about the consequences. Regarding uncertainty: most scientists – and not just most climate scientists, most scientists in general – are pretty certain that the observed global warming over the past 100 years is due to man-made greenhouse gases, and have been for some time. But it seems very difficult to get this message across to the public. One reason is that it is much harder to figure out what the effect of global warming will be at the local level, for example, what will be the average rainfall in the Murray-Darling basin in 2050. It’s harder because calculations involving rainfall are harder to do, since some of the processes involved are not as well understood as they should be, and so the uncertainty is greater. We are dealing here with likelihood and risk management, not certainty. The important thing for scientists (and journalists) is to clearly convey an appreciation of the likelihood of a particular prediction, which will range from almost certain (e.g. that the global temperature will continue to increase, although not always every year) to predictions of much lower certainty. But some predictions ARE certain enough for action to be taken, and it has – like restrictions on the building of new structures close to the coast due to predicted sea level rise, for instance. The only way to reduce uncertainty is with better science.”
Dr Paul Beggs, Senior Lecturer in the Division of Environmental and Life Sciences at Macquarie University
“There is, of course, some uncertainty regarding some aspects of climate change, but we can be sure about many things. I think the public is being underestimated if the media or anyone else thinks it will only act if it has certainty on this issue. The public acts without certainly all the time. Many people are already acting on climate change. While the research on climate change must continue, I look forward to much more community discussion of the many responses to climate change.”
8) How much credence do we give to the central plank of Monckton’s argument that spending loads on cutting carbon will have basically sod all impact on restraining temperature rise?
Professor Steven Sherwood, Climate Change Research Centre at the University of New South Wales
“Monckton has no credibility on this issue and is peddling snake oil. It is true that meaningful reduction will not be easy, but economic studies show that half the job can be accomplished at zero net cost. It just requires changing habits and standing up to some special interest groups.”
9) We hear a lot about the difference between ‘weather’ and ‘climate’, but where do climatologists tend to draw the line? How significant is it, for example, if a given region of Australia were to suffer both its hottest and its driest summer (Dec-Feb) this year? Would that be considered a solid AGW signal or does three months still count as ‘weather’ not ‘climate’?
Professor Steven Sherwood, Climate Change Research Centre at the University of New South Wales
“That would count as weather, not climate. The real question in science is whether observations are consistent with different hypotheses. The snowstorms in Europe and the US, for example, are fully consistent with greenhouse warming predictions: less than one degree of warming will not put an end to snowstorms! The only evidence that matters is that which would be inconsistent with one argument or the other. The observed global warming, and its geographic pattern, is inconsistent with the notion that greenhouse gases have no effect on climate and has been shown so in many independent, peer-reviewed studies.”
Professor Neville Nicholls, Professorial Fellow in the School of Geography and Environmental Science at Monash University, Melbourne
“As the IPCC Fourth Assessment says very clearly, a single extreme event cannot be attributed to global warming (or any other cause). This is the case whether we are talking about a single storm or a single hot summer. But a consistent string of extreme events of the same type – such as the run of unprecedented heat waves that have hit Australia in the past few years – starts to look a lot more like climate change, and less like a fluke.”
10) What greenhouse gas cuts need to be made and by when to achieve certain temperature-rise limits (i.e. of 2 degrees) and to minimise the impact of climate change?
Professor Steven Sherwood, Climate Change Research Centre at the University of New South Wales
“We can predict temperature rises over the long term to about a factor of 2, which isn’t great and means we are dealing here with probabilities. To have a decent chance of avoiding an eventual 2C rise would require that future emissions be roughly equal to all past emissions. This would require emissions to peak in the next decade or so and then decline almost as fast as they rose over the 20th century.”