How the IPCC Underestimated Climate Change

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How the IPCC Underestimated Climate Change
Here are just eight examples of where the IPCC missed predictions
December 6, 2012 |By Glenn Scherer and
Rajenda Pachauri
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Climate Science Predictions Prove Too Conservative
Climate Science Predictions Prove Too Conservative

Scientists will tell you: There are no perfect computer models. All are incomplete representations of nature, with uncertainty built into them. But one thing is certain: Several fundamental projections found in Intergovernmental Panel on Climate Change reports have consistently underestimated real-world observations, potentially leaving world governments at doubt as to how to guide climate policy.

At the heart of all IPCC projections are “emission scenarios:” low-, mid-, and high-range estimates for future carbon emissions. From these “what if” estimates flow projections for temperature, sea-rise, and more.

Projection: In 2001, the IPCC offered a range of fossil fuel and industrial emissions trends, from a best-case scenario of 7.7 billion tons of carbon released each year by 2010 to a worst-case scenario of 9.7 billion tons.

Reality: In 2010, global emissions from fossil fuels alone totaled 9.1 billion tons of carbon, according to federal government’s Earth Systems Research Laboratory.

Why the miss? While technically within the range, scientists never expected emissions to rise so high so quickly, said IPCC scientist Christopher Fields. The IPCC, for instance, failed to anticipate China’s economic growth, or resistance by the United States and other nations to curbing greenhouse gases.

“We really haven’t explored a world in which the emissions growth rate is as rapid as we have actually seen happen,” Fields said.

IPCC models use the emission scenarios discussed above to estimate average global temperature increases by the year 2100.

Projection: The IPCC 2007 assessment projected a worst-case temperature rise of 4.3° to 11.5° Fahrenheit, with a high probability of 7.2°F.

Reality: We are currently on track for a rise of between 6.3° and 13.3°F, with a high probability of an increase of 9.4°F by 2100, according to the Massachusetts Institute of Technology. Other modelers are getting similar results, including a study published earlier this month by the Global Carbon Project consortium confirming the likelihood of a 9ºF rise.

Why the miss? IPCC emission scenarios seriously underestimated global CO2 emission rates, which means temperature rates were underestimated too. And it could get worse: IPCC projections haven’t included likely feedbacks such as large-scale melting of Arctic permafrost and subsequent release of large quantities of CO2 and methane, a greenhouse gas 20 times more potent, albeit shorter lived, in the atmosphere than carbon dioxide.

Arctic Meltdown
Five years ago, the summer retreat of Arctic ice wildly outdistanced all 18 IPCC computer models, amazing IPCC scientists. It did so again in 2012.

Projection: The IPCC has always confidently projected that the Arctic ice sheet was safe at least until 2050 or well beyond 2100.

Reality: Summer ice is thinning faster than every climate projection, and today scientists predict an ice-free Arctic in years, not decades. Last summer, Arctic sea ice extent plummeted to 1.32 million square miles, the lowest level ever recorded – 50 percent below the long-term 1979 to 2000 average.

Why the miss? For scientists, it is increasingly clear that the models are under-predicting the rate of sea ice retreat because they are missing key real-world interactions.

“Sea ice modelers have speculated that the 2007 minimum was an aberration… a matter of random variability, noise in the system, that sea ice would recover.… That no longer looks tenable,” says IPCC scientist Michael Mann. “It is a stunning reminder that uncertainty doesn’t always act in our favor.”

Ice Sheets
Greenland and Antarctica are melting, even though IPCC said in 1995 that they wouldn’t be.

Projection: In 1995, IPCC projected “little change in the extent of the Greenland and Antarctic ice sheets… over the next 50-100 years.” In 2007 IPCC embraced a drastic revision: “New data… show[s] that losses from the ice sheets of Greenland and Antarctica have very likely contributed to sea level rise over 1993 to 2003.”

Reality: Today, ice loss in Greenland and Antarctica is trending at least 100 years ahead of projections compared to IPCC’s first three reports.

Why the miss? “After 2001, we began to realize there were complex dynamics at work – ice cracks, lubrication and sliding of ice sheets,” that were melting ice sheets quicker, said IPCC scientist Kevin Trenberth. New feedbacks unknown to past IPCC authors have also been found. A 2012 study, for example, showed that the reflectivity of Greenland’s ice sheet is decreasing, causing ice to absorb more heat, likely escalating melting.

Sea-Level Rise
The fate of the world’s coastlines has become a classic example of how the IPCC, when confronted with conflicting science, tends to go silent.

Projection: In the 2001 report, the IPCC projected a sea rise of 2 millimeters per year. The worst-case scenario in the 2007 report, which looked mostly at thermal expansion of the oceans as temperatures warmed, called for up to 1.9 feet of sea-level-rise by century’s end.

Today: Observed sea-level-rise has averaged 3.3 millimeters per year since 1990. By 2009, various studies that included ice-melt offered drastically higher projections of between 2.4 and 6.2 feet sea level rise by 2100.

Why the miss? IPCC scientists couldn’t agree on a value for the contribution melting Greenland and Antarctic ice sheets would add to sea-level rise. So they simply left out the data to reach consensus. Science historian Naomi Oreskes calls this – one of IPCC’s biggest underestimates – “consensus by omission.”

Ocean Acidification
To its credit, the IPCC admits to vast climate change unknowns. Ocean acidification is one such impact.

Projection: Unmentioned as a threat in the 1990, 1995 and 2001 IPCC reports. First recognized in 2007, when IPCC projected acidification of between 0.14 and 0.35 pH units by 2100. “While the effects of observed ocean acidification on the marine biosphere are as yet undocumented,” said the report, “the progressive acidification of oceans is expected to have negative impacts on marine shell-forming organisms (e.g. corals) and their dependent species.”

Reality: The world’s oceans absorb about a quarter of the carbon dioxide humans release annually into the atmosphere. Since the start of the Industrial Revolution, the pH of surface ocean waters has fallen by 0.1 pH units. Since the pH scale is logarithmic, this change represents a stunning 30 percent increase in acidity.

Why the miss? Scientists didn’t have the data. They began studying acidification by the late 1990s, but there weren’t many papers on the topic until mid-2000, missing the submission deadline for IPCC’s 2001 report. Especially alarming are new findings that ocean temperatures and currents are causing parts of the seas to become acidic far faster than expected, threatening oysters and other shellfish.

National Oceanic and Atmospheric Administration chief Jane Lubchenco has called acidification the “equally evil twin” to global warming.

Thawing Tundra
Some carbon-cycle feedbacks that could vastly amplify climate change – especially a massive release of carbon and methane from thawing permafrost – are extremely hard to model.

Projection: In 2007, IPCC reported with “high confidence” that “methane emissions from tundra… and permafrost have accelerated in the past two decades, and are likely to accelerate further.” However, the IPCC offered no projections regarding permafrost melt.

Reality: Scientists estimate that the world’s permafrost holds 1.5 trillion tons of frozen carbon. That worries scientists: The Arctic is warming faster than anywhere else on earth, and researchers are seeing soil temperatures climb rapidly, too. Some permafrost degradation is already occurring.

Large-scale tundra wildfires in 2012 added to the concern.

Why the miss? This is controversial science, with some researchers saying the Arctic tundra is stable, others saying it will defrost only over long periods of time, and still more convinced we are on the verge of a tipping point, where the tundra thaws rapidly and catastrophically. A major 2005 study, for instance, warned that the entire top 11 feet of global permafrost could disappear by century’s end, with potentially cataclysmic climate impacts.

The U.N. Environmental Programme revealed this week that IPCC’s fifth assessment, due for release starting in September, 2013, will again “not include the potential effects of the permafrost carbon feedback on global climate.”

Tipping points
The IPCC has been silent on tipping points – non-linear “light switch” moments when the climate system abruptly shifts from one paradigm to another.

Projection: IPCC has made no projections regarding tipping-point thresholds.

Reality: The scientific jury is still out as to whether we have reached any climate thresholds – a point of no return for, say, an ice-free Arctic, a Greenland meltdown, the slowing of the North Atlantic Ocean circulation, or permanent changes in large-scale weather patterns like the jet stream, El Niño or monsoons. The trouble with tipping points is they’re hard to spot until you’ve passed one.

Why the miss? Blame the computers: These non-linear events are notoriously hard to model. But with scientists recognizing the sizeable threat tipping points represent, they will be including some projections in the 2013-14 assessment.

This article originally appeared at The Daily Climate, the climate change news source published by Environmental Health Sciences, a nonprofit media company.
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Sisko December 6, 2012, 1:22 PM

The writer of this article; Glenn Scherer, seems to promote the spreading of inaccurate propaganda and untrue statements which seems typical of this publication. He writes “scientists believe” vs. accurately writing that some individual person or scientist believes without acknowledging that there are many, many other scientists who view the situation differently.

Let’s review some of the claims in this propaganda piece by Scherer

He wrote- “The IPCC’s overly conservative reading of the science, they say, means governments and the public could be blindsided by the rapid onset of the flooding, extreme storms, drought, and other impacts associated with catastrophic global warming.”

My response- Idiots try to claim that any recent bad weather has been caused by cAGW but when you look at the actual long term data trends you find that there is not any significant change from the long term data. Notice how Scherer did not post the link to any data that supported the claimed increase in flooding, extreme storms, drought, etc. in any particular area.

He wrote: “Sea-level rise is another. In its 2001 report, the IPCC predicted an annual sea-level rise of less than 2 millimeters per year. But from 1993 through 2006, the oceans actually rose 3.3 millimeters per year, more than 50 percent above that projection.”

My response- We have had measurements of sea level rise since late 1992 and that data has shown a consistent rate of rise of about 3mm per year. It has not increased in the entire time we have had reasonably accurate measurements. The rate of rise will have to more than double to reach the lower end of the IPCC predicted rise of approximately .6 meters by 2100. There being ZERO evidence of a change in the rate of rise from the non threatening 1 foot per century rate we are seeing.

He wrote- “In November, scientists at the National Center for Atmospheric Research in Boulder, Colo., took a closer look at the computer models underpinning most climate predictions and concluded future warming is likely to be on the high side of climate projections.”

My response- This one is the spreading of untruth. The fact is that the computer models the IPCC used have overstated the rate of temperature rise and not understated it has been reported. I have attached the link to the actual analysis.
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Cramer Sisko December 6, 2012, 2:46 PM


Most “scientists believe” your statements are “inaccurate propaganda and untrue statements.” Everything you said has been debunked numerous times on this site and elsewhere.

Regardless of one’s belief of the relative accuracy of satellite observations versus tide gauges, sea level rise was not anywhere close to 3.3 mm/yr over the 19th and 20th centuries. You seem to believe it was, which then allows you to believe there is no acceleration. Tide gauges have also showed the same acceleration.

The premise is that IPCC projected less 2 mm/yr in 2001 and it was underestimated. Are you claiming this was NOT an underestimate?
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Cramer Sisko December 6, 2012, 2:52 PM

Sisko is always in error because he cherry-picks.

When there’s an article/comment about long-term temperature and sea level TRENDS focusing on projections to the year 2100 AD, he only concentrates on volatile short-term data for the last ten years.

When there’s an article/comment about increased VOLATILITY of observed short-term data, Sisko closes his eyes to that volatility and only looks at long term trends (100 year datasets of rainfall in Nebraska and Colorado to claim droughts are not out of the ordinary).
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Sisko Cramer December 6, 2012, 3:22 PM


You just do not like to admit when you are wrong, but you should be used to it since it has been shown so frequently.

I have made no claims about sea level pre 1992 when accurate measurement have been available. Since that time is has been rising at a pretty steady rate that would have to double to meet the IPCC forecast. You on the other hand seem to rely upon what I believe you know are very poor records of sea level prior to our having data from satellites to measure seal level worldwide.

Please Cramer, attempt to show ANY of the propaganda written by Scherer to be accurate. Show where there has been an unusual drought trend somewhere unprecedented historically. You seem to like to claim bad things are happening without evidence to support the claim. (kind of like your and the author of this propaganda do on sea level change.
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criordon December 6, 2012, 3:46 PM

“Reality: In 2011, Global emissions totaled 31.6 billion tons of carbon, according to the International Energy Agency, exceeding IPCC’s worst-case scenario 88 years ahead of schedule.”

Sorry, but this is fiction, not fact. Scherer has made a fundamental error here, of the type not generally found in SciAm articles. He has confused ‘carbon’ with ‘carbon dioxide’. Perhaps a basic course in chemistry might be in order for this writer before he attempts any more articles of this type. The amount of carbon contained in 31.6 GT of CO2 is less than 40% of the mass of the CO2 in question in this paragraph, or just under 12 GT of carbon. The figures cited by Mr. Scherer are for the annual human contribution of CO2 to the atmosphere, not that of carbon.

As for the rest of the article, it is passable, but repeats what we who have been reading science regularly have known for many years now, that our combustion of fossil fuels is changing the planet’s atmosphere and warming the world. This has been evident since the 1980s or earlier. However, as evidenced by some of the seemingly disbelieving comments before mine, this repetition of seemingly basic facts will likely be necessary for some time to come, as some people would rather attempt make up their own reality than accept the one revealed by scientific research.

So, keep on repeating the message until it sinks in, but please, try to get the facts right. If you don’t do the fact checking, someone else like me will do it, and it always looks better if you get it right the first time.
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criordon December 6, 2012, 4:06 PM

Just a quick comment to Sisko and Cramer on the sea-level rise issue. Keep in mind that the RATE of rise is increasing or accelerating, not constant, and this will account for the predicted rise in sea levels forecast by the IPCC. Naturally, there are still many unknowns in the details, but the main trends are apparent, and the models converge on the range of estimates provided, unless new and previously unconsidered factors come to light (which is not impossible).

We would be wise to note that so far, these unknowns have generally proven that our case is worse than we originally estimated, not better, a trend which may continue however much we wish otherwise, as we push research further. Ice requires huge quantities of energy to melt, but once it is melted, then the temperature of the water starts to increase, which in turn melts the ice faster, etc.

One thing many people fail to understand in this phenomenon is the huge systemic inertia which must initially be overcome before there are clearly measurable changes – I think we can now say that the initial inertia is overcome, and the warming process is in motion. It is important to realize that the process will not stop if we stop emitting fossil CO2, but gradually slow down (i.e warming will continue, but at a gradually decreasing rate until equilibrium is reached again) over a period of decades or centuries, and I see no serious signs that we will stop emitting fossil CO2 any time soon.
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Cramer Sisko December 6, 2012, 4:07 PM


You have already confirmed that sea level has been rising by at least 3 mm/yr since the early 1990s. You have also said there is no proof of acceleration. Please provide evidence that sea level was rising at a rate of 3 mm/yr in the 19th and 20th centuries. When 100 years projections are being made, you might want to consider more data than just 20 years of data.

You are the one claiming that Glen Scherer is wrong (not only that but you seem to be calling him a liar). He has provided plenty of details and references. You have provided nothing but misframed arguments, anecdotes, gut feelings, and an analysis of only ten years of data at The onus is one you to provide the evidence that he is wrong, especially after such libelous statements (which says something about your level of scientific expertise).

It is simple: show us that IPCC did not make the projections Scherer claims they made in their 1990, 1995, 2001, and 2007 IPCC reports. And/or show us that the new observations are wrong.

For example:

1. “In the 2001 report, the IPCC projected a sea rise of 2 millimeters per year. … Observed sea-level-rise has averaged 3.3 millimeters per year since 1990.”

Either prove that this was not in the 2001 report and/or prove that sea level is not currently rising faster than 2 mm/yr. You already agreed it’s been rising at 3 mm/yr, so I can only guess you believe the 2 mm/yr projection was not in the 2001 IPCC report.

2. In the 2001 report IPCC projected CO2 emissions of 8 to 30 billion tons/yr by 2100. CO2 emissions in 2011 were 31.6 billion tons.

Prove any of these numbers wrong.

And I could continue, but I am hoping that you might now understand how to properly refute the claims you say are not true.
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PTGoodman Sisko December 6, 2012, 4:09 PM


There is absolutely no way of getting through to people like you–believe me, I’ve tried. So we try to make progress w/o you.
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Cramer criordon December 6, 2012, 4:13 PM


Sisko has said many times that there is zero proof the acceleration of sea level rise. Not I.

Please address your statements to him (and please use the reply button).
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pabelmont December 6, 2012, 4:27 PM

A very lively discussion. How many of the writers believe that there will be a lively discussion of this issue (or of anything much) in, say, 2050?

I know, the models say nothing about the frequency and duration of discussions.
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