Global warming 'hiatus' puts climate change scientists on the spot

Sep 23, 2013 by Monte Morin

It's a climate puzzle that has vexed scientists for more than a decade and added fuel to the arguments of those who insist man-made global warming is a myth. Since just before the start of the 21st century, the Earth's average global surface temperature has failed to rise despite soaring levels of heat-trapping greenhouse gases and years of dire warnings from environmental advocates.

Now, as scientists with the Intergovernmental Panel on Climate Change gather in Sweden this week to approve portions of the IPCC's fifth assessment report, they are finding themselves pressured to explain this glaring discrepancy.

The panel, a United Nations creation that shared the 2007 Nobel Peace Prize with Al Gore, hopes to brief world leaders on the current state of science in a clear, unified voice. However, experts inside and outside the process say members probably will engage in heated debate over the causes and significance of the so-called hiatus.

"It's contentious," said IPCC panelist Shang-Ping Xie, a professor of at the Scripps Institution of Oceanography at the University of California, San Diego. "The stakes have been raised by various people, especially the skeptics."

Though scientists don't have any firm answers, they do have multiple theories. Xie has argued that the hiatus is the result of heat absorption by the Pacific Ocean - a little-understood, naturally occurring process that repeats itself every few decades. Xie and his colleagues presented the idea in a study published last month in the prestigious journal Nature.

The theory, which is gaining adherents, remains unproved by actual observation. Surface temperature records date back to the late 1800s, but measurements of deep water temperature began only in the 1960s, so there just isn't enough data to chart the long-term patterns, Xie said.

Scientists have also offered other explanations for the hiatus: lack of sunspot activity, low concentrations of atmospheric water vapor and other marine-related effects. These too remain theories.

For the general public, the existence of the hiatus has been difficult to reconcile with reports of record-breaking summer heat and precedent-setting Arctic ice melts.

At the same time, those who deny the tenets of climate change science - that the burning of fossil fuels adds carbon dioxide and other greenhouse gases to the atmosphere and warms it - have seized on the hiatus, calling it proof that global warming isn't real.

Climate scientists, meanwhile, have had a different response. Although most view the pause as a temporary interruption in a long-term warming trend, some disagree and say it has revealed serious flaws in the deliberative processes of the IPCC.

One of the most prominent of these critics is Judith Curry, a climatologist who heads the School of Earth and Atmospheric Sciences at the Georgia Institute of Technology. She was involved in the third IPCC assessment, which was published in 2001. But now she accuses the organization of intellectual arrogance and bias.

"All other things being equal, adding more greenhouse gases to the atmosphere will have a warming effect on the planet," Curry said. "However, all things are never equal, and what we are seeing is natural climate variability dominating over human impact."

Curry isn't the only one to suggest flaws in established climate models. IPCC Vice Chair Francis Zwiers, director of the Pacific Climate Impacts Consortium at the University of Victoria in Canada, co-wrote a paper published in this month's Nature Climate Change that said climate models had "significantly" overestimated global warming over the last 20 years - and especially for the last 15 years, which coincides with the onset of the hiatus.

The models had predicted that the average global surface temperature would increase by 0.21 of a degree Celsius over this period, but they turned out to be off by a factor of four, Zwiers and his colleagues wrote. In reality, the average temperature has edged up only 0.05 of a degree Celsius over that time - which in a statistical sense is not significantly different from zero.

Of course, people don't actually spend their entire lives subjected to the global average temperature, which is currently about 15 degrees Celsius, or 59 degrees Fahrenheit. Those who fixate on that single measurement lose sight of significant regional trends, particularly in the Northern Hemisphere, climate scientists say.

Xie and Yu Kosaka, an assistant project scientist at Scripps, used computer models to simulate the Pacific decadal oscillation, a phenomenon related to the El Nino and La Nina ocean temperature cycles that lasts for 20 to 30 years. The model suggested that the northern mid-latitudes - an area that includes the United States and most of Europe and China - were "insulated" from the oscillation's cooling effect during the summer months, as was the Arctic region.

"In the summer you've basically removed the Pacific cooling, so we're still baked by greenhouse gases," Xie said.

As a consequence, 2012 marked two climate milestones, he said. The U.S. experienced its hottest year on record, while ice cover in the North Pole shrank to the lowest level ever observed by satellite.

Other climatologists, such as Bill Patzert of NASA's Jet Propulsion Laboratory in La Canada Flintridge, Calif., say sea level rise is "unequivocal proof" that are continuing to heat the planet, and that much of this added heat is being absorbed by the oceans.

As ocean water warms, it expands and drives sea levels higher, Patzert said. Currently, oceans are rising at an average of more than 3 millimeters, or 0.12 of an inch, per year. This pace is significantly faster than the average rate over the last several thousand years, scientists say.

"There's no doubt that in terms of global temperatures, we've hit a little flat spot in the road here," Patzert said. "But there's been no slowdown whatsoever in sea level rise, so global warming is alive and well."

Whether that message is communicated successfully by the IPCC this week remains to be seen. In the days leading up to the meeting, the organization has found itself on the defensive.

A draft summary that was leaked to the media reported that scientists were "95 percent confident" that human activity was responsible for more than half of the increase in average between 1951 and 2010. But critics openly scoff, considering the IPCC's poor record for predicting short-term temperature increases.

"This unpredicted hiatus just reflects the fact that we don't understand things as well as we thought," said Roger Pielke Jr., a professor of environmental studies at the University of Colorado in Boulder and vocal critic of the climate change establishment. "Now the IPCC finds itself in a position that a science group never wants to be in. It's in spin management mode."

Explore further: Climate: Growing certainties on warming and human role

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Water_Prophet
1 / 5 (17) Sep 23, 2013
Scientist do not understand the blessing of Water.
The Water's beneficent avatar ice thrives at the Earths poles and Greenland (blessed is the green land that is white with Water's beneficence!).
When man blasphemes and puts heat, the accursed Air Elemental CO2 into the world and would otherwise cause heating, the blessed Ice melts, causing the temperature to remain buffered, if not constant. Like unto ice in your glass in the Summer.
Blessed and forgiving is the Water!
Men take heed, even the blessed Element's forbearance is not infinite! Repent!
Maggnus
3.2 / 5 (13) Sep 23, 2013
What I find most interesting is the fact that climate scientists the world over are saying that while we don't understand for sure what is causing this "hiatus", that every other measure we have says warming is continuing. They admit, freely, that we are dealing with a very complex system, and that we do not have every answer.

Yet denialists (not skeptics) seize on any little thing to try and promote their political bent on the subject and hysterically cry conspiracy because some aspect of the warming does not conform perfectly with 30 year old predictions.

If (actually, more likely when) the Pacific decadal oscillation flips and surface temperatures warm faster than would be expected but for CO2 loading of the atmosphere, will we hear Ms Curry and Mr Zwiers say they were wrong? Probably yes - but it will be too late, and there will be nothing humans can do to prevent the catastrophic change such warming will cause.

A slower rise than predicted is still a rise!
dav_daddy
1.9 / 5 (17) Sep 24, 2013
Not slower, basically NONE. .05 is effectively 0.
Moebius
2.8 / 5 (11) Sep 24, 2013
The effect of instability added to a system is fluctuation or oscillation. With that in mind it's easy to predict the effects of global warming. There is an old saying, the lull comes before the storm.
Water_Prophet
1 / 5 (15) Sep 24, 2013
The effect of instability added to a system is fluctuation or oscillation. With that in mind it's easy to predict the effects of global warming. There is an old saying, the lull comes before the storm.

This is an interesting prophesy: The lull being caused by a change in the melting rate vs area of global ice-?
Is this your position?
Fascinating, and well worthy of meditation and examination of scripture.
dtxx
1.8 / 5 (16) Sep 25, 2013
The term denier is so biased sounding. There isn't clear enough evidence of global warming for me to accept that what is happening could not be normal behavior for a complex system like the atmosphere. If I were presented with evidence convincing enough, I would gladly change my position. And my position is that we can't say either way, AGW yes or AGW no.

As you may have noticed, climates do change. Titanboa lived during the much warmer paleocene and could get up to 2500 lbs. Surely the climate has changed much more by natural processes since then than because of anything humans have done.

I also don't think change and extinction is always negative. We all owe our being here now to many massive extinctions throughout history. It's sad when the last of something cute and cuddly dies, but it makes way for new species, new niches to be carved, and fascinating new evolutionary adaptations.
Water_Prophet
1 / 5 (15) Sep 25, 2013
@dtxx, the signs are many and profound, but alas, like a shooting at a mall, we are so inundadted by the evidence, we disregard it.
The Water shows us the evidence: The message is written hastily in ice, and is revealed when it melts away.
ryggesogn2
1.5 / 5 (15) Sep 25, 2013
", but measurements of deep water temperature began only in the 1960s, so there just isn't enough data to chart the long-term patterns, Xie said."

How convenient and it keeps the gravy train rolling.
"Curry isn't the only one to suggest flaws in established climate models."
What? There are climate scientists critical of the the climate models?
""This unpredicted hiatus just reflects the fact that we don't understand things as well as we thought," said Roger Pielke Jr.,'

Not according to many who post here. THEY know it all.
Water_Prophet
1 / 5 (15) Sep 25, 2013
@ryggesongn2-The expectations of the Blessed Sea are that temperature should (sufficiently) isolated from the surface environment that changes are not expected.
Xie does not know his scripture, presumably.