A pause for this message: climate change numbers aren’t adding...

A pause for this message: climate change numbers aren’t adding up

• THE AUSTRALIAN
• OCTOBER 18, 2014 12:00AM

Graham Lloyd

Environment Editor
Sydney


“Global mean surface temperatures rose rapidly from the 1970s but have been relatively flat over the most recent 15 years to 2013.” British MET office. Source: Supplied
SCIENCE, like climate, can take a long time to change direction.
When Intergovernmental Panel on Climate Change chairman Rajendra Pachauri first acknowledged to this newspaper in February last year the existence of a pause in global surface temperatures of more than a decade, his comments were met with incredulity.
But as the political and diplomatic world strives to deliver meaningful action on climate change, momentum is building behind the controversial view that the numbers don’t add up.
A rising chorus of literature in the world’s best scientific journals and most prestigious opinion pages has argued the climate change math is flawed. Like a freight train that has left the station, questions about an 18-year “hiatus” in global average surface temperatures and the location of “missing” heat from the climate system are building a head of steam.
For climate scientists, irritating questions from “sceptics” about the “pause” have now become peer-reviewed papers that suggest the Earth’s climate may be much less sensitive to higher levels of carbon dioxide than predicted.
Michael Asten, from the school of earth atmosphere and environment at Monash University, says there have been 15 articles commenting on and analysing the pause, or hiatus, published by the top journal group Nature in the past two years.
“While opinions on causes differ, existence of the pause is settled; only activists dare claim the pause in global temperature does not exist,” Asten says.
For scientists such as Matthew England, from University of NSW Climate Change Research Centre, the “missing heat” will reappear with a vengeance. But it is unclear when this will happen.
There is no dispute that the level of carbon dioxide in the atmosphere is rising, that human actions are contributing to the rise and, all things being equal, this will have an impact on the Earth’s climate.
But while the IPCC says it is more certain than ever that humans are causing climate change, the gap between what climate models have predicted should happen and what is being observed is growing.
Clearly, in nature, all things are not equal and the uncertainties of scientific understanding continue to be great. This week, fresh science has shed new light on how plants use more CO2 than previously thought. We now know plankton growth in the Arctic Ocean accelerates with increasing UV light, locking up more carbon. Complex processes are layered over complex systems that occur across timeframes longer than scientists have been able to physically measure them.
Key questions remain about the impact of clouds and ocean cycles and the true level of climate sensitivity to CO2.
It is a crucial time for science.
Garth Paltridge, former chief research scientist with the CSIRO Division of Atmospheric Research and chief executive of the Antarctic Co-operative Research Centre, fears the rise of “postmodern” science. In the world of postmodern science, he says, results are valid only in the context of society’s beliefs, and where the very existence of scientific truth can be denied.
“Postmodern science envisages a sort of political nirvana in which scientific theory and results can be consciously and legitimately manipulated to suit either the dictates of political correctness or the politics of the government of the day,” Paltridge says.
At this point, Australian governments and their climate agencies are standing firmly behind the IPCC. But respected US climate scientist Judith Curry agrees with Paltridge. Curry is a professor and former chairwoman of the school of earth and atmospheric Sciences at the Georgia Institute of Technology. She has served on the NASA Advisory Council Earth Science Subcommittee, National Academies Climate Research Committee and the Space Studies Board, and the National Oceanic and Atmospheric Administration Climate Working Group.
Curry has been a strong voice in the climate change debate internationally and is at the centre of new research that questions climate sensitivity. She argues the sensitivity of the climate to increasing concentrations of carbon dioxide is a central question in the debate on the appropriate policy response to increasing carbon dioxide in the atmosphere.
In the US, she says, a climate policy dialogue is starting to open up, with discussion of the 2C threshold, lower sensitivity and the hiatus.
Climate sensitivity is defined as the global surface warming that occurs when the concentration of carbon dioxide in the atmosphere doubles. High sensitivity will lead to substantial warming as atmospheric CO2 continues to increase. If climate sensitivity is low, Curry says, future warming will be substantially lower and it may be several generations before average temperatures move past the 2C limit set for dangerous warming.
According to the IPCC’s latest report, the actual change in 70 years if the level of CO2 in the atmosphere doubles — known as the transient climate response — is likely to be in the range of 1C to 2.5C. Curry says most climate models have transient climate response values exceeding 1.8C. The IPCC report notes, however, there is a substantial discrepancy between recent observation-based estimates of climate sensitivity and estimates from climate models.
In Curry’s calculation, the best estimate for transient climate response is 1.33C with a likely range of 1.05C to 1.80C. Her observation-based energy-balance approach calculations use the same data as the IPCC’s latest report for the effects on the Earth’s energy balance of changes in greenhouse gases, aerosols and other drivers of climate change.
The Curry paper also estimates what the long-term warming from a doubling of carbon dioxide concentrations will be, once the deep ocean has warmed up.
“Our estimates of sensitivity, both over a 70-year timeframe and long term, are far lower than the average values of sensitivity determined from global climate models that are used for warming projections,” Curry says.
“Also, our ranges are narrower, with far lower upper limits than reported by the IPCC’s latest report. Even our upper limits lie below the average values of climate models.”
Curry says more than a dozen other observation-based studies havde found climate sensitivity values lower than those determined using global climate models, including recent papers in prestigious climate journals.
She says the new climate sensitivity estimates add to the growing evidence that climate models are running “too hot”.
“Moreover, the estimates in these empirical studies are being borne out by the much-discussed ‘pause’ or ‘hiatus’ in global warming — the period since 1998 during which global average surface temperatures have not significantly increased,” she says.
The pause in warming is at odds with the 2007 IPCC report, which expected warming to increase at a rate of 0.2C per decade in the early 21st century.
Curry says the warming hiatus, combined with assessments that the climate-model sensitivities are too high, raises serious questions as to whether the climate-model projections of 21st-century temperatures are fit for making public policy decisions.
Inquirer put a series of questions to Australia’s high-profile climate change bodies asking them to comment on Curry’s research on climate sensitivity, the hiatus in global surface temperatures and model predictions.
Former climate commissioners Will Steffen and Tim Flannery were unavailable to answer but Climate Council chief executive Amanda McKenzie says “vested interests have been using the ‘so-called pause’ to spread doubt and misinformation”.
“The Earth continues to warm strongly,” she says. “Since 1998 human activities have introduced two billion Hiroshima bombs’ worth of heat into the atmosphere.”
David Karoly, from the school of earth sciences at the University of Melbourne, says “the 18-year period 1996 to 2013 has a warming trend in global average surface temperature that is not significantly different than the long-term warming trend 1950 to 2012”.
“It is slightly smaller in magnitude than the long-term warming trend, but that difference is not statistically significant,” Karoly says. He says the reduction in the rate of surface warming for the recent 15 years demonstrates that natural internal variability of the climate system is very important and that exchanges of heat between the surface and the deeper ocean are very important.
Karoly says he believes “some climate models underestimate … and some models overestimate the global climate sensitivity”.
“The most plausible explanation is natural decadal variability of the climate system.”
Responses from Australia’s key science organisations show they remain in lock-step with the IPCC and their advice is accepted by Environment Minister, Greg Hunt.
Helen Cleugh, science director at CSIRO Oceans and Atmosphere Flagship, says measurements do show that the rate at which global mean surface temperature has warmed in the past decade is less than the previous decade. However, while the rate of increase is lower, the temperatures are not lower, she says.
Measurements across the oceans and Earth system as a whole show that warming has continued unabated. “A reduction in the rate of warming (not a pause) is a result of short-term natural variability, ocean absorption of heat from the atmosphere, volcanic eruptions, a downward phase of the 11-year solar cycle, and other impacts over a short time period,” Cleugh says.
After taking advice from the Bureau of Meteorology, Hunt tells Inquirer the warming of the climate system is “unequivocal”.
“The climate system, which includes the atmosphere, oceans, land and ice has continued to accumulate heat over the last 18 years,” Hunt says. Although there has been a slower rate of atmospheric warming during the past 18 years, this does not undermine the fundamental physics of global warming, the scientific basis of climate models or the estimates of climate sensitivity.
However, he says he is “exceptionally interested” in the latest reports that there may be even greater capacity for plants and soil to absorb carbon. “While this will be the subject of significant global research over coming years, it underscores the importance of protecting the great rainforests of the world and helping to revegetate our landscapes,” he says.
Greens leader Christine Milne says she does not accept the pause.
“There has been a slowdown in the speed of the rise but global surface temperatures have still continued to climb,” Milne says. “There are strong indications through observations and models that the ocean is absorbing more of the heat than it has in the recent past.”
In Britain, the Met Office has acknowledged the pause and debate about its significance.
“Global mean surface temperatures rose rapidly from the 1970s but have been relatively flat over the most recent 15 years to 2013,” the Met says. “This has prompted speculation that human induced global warming is no longer happening, or at least will be much smaller than predicted.
“Others maintain that this is a temporary pause and that temperatures will again rise at rates seen previously,” the Met says.
But the Met Office says research shows the recent pause in global surface temperature rise does not materially alter the risks of substantial warming of the Earth by the end of this century.
“Nor does it invalidate the fundamental physics of global warming, the scientific bases of climate models and their estimates of climate sensitivity,” the Met says.
Australia’s Bureau of Meteorology says the rate of warming in global surface temperature during the past century has not been uniform, with some decades warming more rapidly than others.
“This is a consequence of variations in heat exchange between the atmosphere and the oceans, and other decade-to-decade changes like variations in solar forcing and the solar dimming effects of pollution and volcanic eruptions,” BoM says.
“The pattern that results is one of steady warming of the oceans, accompanied by alternating periods of fast and slow rises in air temperature.”
There is dispute over whether increased ocean heat can fully explain the absence of surface warming during the past 18 years. Recent papers have claimed greater deep ocean heat in the north Pacific, Atlantic and Southern Ocean to explain the “missing” heat.
According to Curry, the bottom line is that uncertainties in ocean heat content are very large, and “there is no particularly convincing evidence that the “missing heat” is hiding in the ocean.
Asten, at Monash, says the hiatus demonstrates a disconnect between climate models up to 2013 (the IPCC Fifth Assessment Report) and physical measurements on our “laboratory Earth”.
There are multiple possible explanations for the disconnect, he says.
UNSW’s England and co-workers have proposed a mechanism of transport of heat on a warming Earth from the ocean surface into the deep ocean via changes in the interaction of trade winds and ocean currents.
Gerald Meehl and colleagues at the National Centre for Atmospheric Research in Colorado have shown from climate models that a mechanism may exist whereby in El Nino conditions a greater proportion of global heat is stored in oceans below 300m, whereas in La Nina conditions that greater proportion is stored in the upper ocean, although tuning climate models to replicate this process has had only limited success.
William Llovel and co-workers at the California Institute of Technology, in a study published two weeks ago, shows with quantitative observations on global ocean mass and temperature profiles that the deep ocean has cooled slightly, not warmed, in the past decade, and thus the explanation of heat transfer from a warming Earth surface into deep oceans becomes less credible.
“The three studies represent careful studies using conventional assumptions relating to climate sensitivity, addressing the question ‘where has the heat in a warming earth gone?’ ” Asten says.
“An alternative approach which I predict will come, although not without opposition from ‘consensus scientists’, is to postulate that the ‘missing heat’ was never here; that is, a reduced climate sensitivity will be estimated for the Earth, at or below the low end of the range currently published by the IPCC.”
Asten says the trend of climate sensitivity estimates made across the past six years from meteorological, satellite and ocean sediment records has been, with very few exceptions, to produce estimates at or below the low end of the range published by the IPCC.
He says low values of climate sensitivity will still affect global temperatures as CO2 concentrations in the atmosphere rise, but increases in temperature may be of similar magnitude to naturally driven temperature cycles, a scenario that has strong implications for how we manage causes and consequences of climate change.
Paltridge says that the prospect of “missing heat” being located in the oceans is a double-edged sword.
“We are being told that some internal oceanic fluctuation may have reduced the upward trend in global temperature,” he says.
“It is therefore more than a little strange that we are not hearing from the IPCC that some natural internal fluctuation of the system may have given rise to most of the earlier upward trend.
“In light of all this, we have at least to consider the possibility that the scientific establishment behind the global warming issue has been drawn into the trap of seriously overstating the climate problem in its effort to promote the cause.
“It is a particularly nasty trap in the context of science because it risks destroying, perhaps for centuries to come, the unique and hard-won reputation for honesty which is the basis of society’s respect for scientific endeavour.”

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