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IPCC: Climate Warming Unequivocal, Human Activity Very Likely (>90% Probability) Causing Most

Comparison of observed continental- and global-scale changes in surface temperature (black line) with results simulated by climate models using natural and anthropogenic forcings. Click to enlarge.

Warming of the world’s climate system is “unequivocal”, most of the observed increase in globally averaged temperatures since the mid-20th century is “very likely” due to the increase in greenhouse gas concentrations caused by anthropogenic emissions, and continued greenhouse gas emissions at or above current rates will cause further warming and induce many changes in the global climate that would “very likely” be larger than those observed during the 20th century, according to the just-released Summary of the first volume of “Climate Change 2007”—also known as the Fourth Assessment Report (AR4)—by Working Group I of the Intergovernmental Panel on Climate Change (IPCC).

Very likely,” as used in the Summary, indicates a greater than 90% probability, using expert judgement, of an outcome or a result. This assessment reflects a greater confidence in the role of anthropogenic emissions than in the prior report in 2001, when their role was deemed “likely”—greater than 66% probability.

Global-average radiative forcing (RF) estimates and ranges in 2005 for anthropogenic carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O) and other important agents and mechanisms, together with the typical geographical extent (spatial scale) of the forcing and the assessed level of scientific understanding (LOSU). Click to enlarge.

The entire Climate Change 2007 report will comprise three main volumes resulting from the efforts of three working groups:

  • Working Group I: The Physical Science Basis (Release 2 February 2007)
  • Working Group II: Impacts, Adaptation and Vulnerability (Acceptance and approval 2-5 April 2007)
  • Working Group III: Mitigation of Climate Change (Acceptance and approval 30 April - 3 May 2007)
  • A short 30-page synthesis report

Climate Change 2007: The Physical Science Basis assesses the current scientific knowledge of the natural and human drivers of climate change, observed changes in climate, the ability of science to attribute changes to different causes, and projections for future climate change. The document released today is a summary of that work.

The report was produced by some 600 authors from 40 countries. More than 620 expert reviewers and a large number of government reviewers also participated. Approximately 300 delegates from 113 countries reviewed and revised the Summary line-by-line during the course of this past week before adopting it and accepting the underlying report. Acceptance is through consensus; the implications is that whatever is accepted and approved has the acceptance of all the participating governments.

While you may probably feel that there is no direct connection between the physical science related to climate change and mitigation options which require actions, let’s say, in reducing or improving the efficiency of fossil fuel use, there is a direct connection because if you see the extent to which human activities are influencing the climate system, then the options for mitigation of the emissions of greenhouse gases appear in a totally different are able to see then what the costs of inaction are.

—Dr Rajendra K Pachauri, Chairman, IPCC
Atmospheric concentrations of carbon dioxide, methane and nitrous oxide over the last 10,000 years (large panels) and since 1750 (inset panels). Measurements are shown from ice cores (symbols with different colours for different studies) and atmospheric samples (red lines). The corresponding radiative forcings are shown on the right hand axes of the large panels. Click to enlarge.

Key findings of the report include:

  • Global atmospheric concentrations of carbon dioxide, methane and nitrous oxide have increased markedly as a result of human activities since 1750 and now far exceed pre-industrial values determined from ice cores spanning many thousands of years. The global increases in carbon dioxide concentration are due primarily to fossil fuel use and land-use change, while those of methane and nitrous oxide are primarily due to agriculture.

  • There is a very high confidence that the globally averaged net effect of human activities since 1750 has been one of warming, with a radiative forcing of +1.6 [+0.6 to +2.4] W m-2.

  • Warming of the climate system is unequivocal, as is now evident from observations of increases in global average air and ocean temperatures, widespread melting of snow and ice, and rising global mean sea level.

  • At continental, regional, and ocean basin scales, numerous long-term changes in climate have been observed. These include changes in Arctic temperatures and ice, widespread changes in precipitation amounts, ocean salinity, wind patterns and aspects of extreme weather including droughts, heavy precipitation, heat waves and the intensity of tropical cyclones. Some aspects of climate have not been observed to change.

  • Paleoclimate information supports the interpretation that the warmth of the last half century is unusual in at least the previous 1,300 years. The last time the polar regions were significantly warmer than present for an extended period (about 125,000 years ago), reductions in polar ice volume led to 4 to 6 meters of sea level rise.

  • Ar44
    Projected warming for different scenarios, shown as continuations of the 20th century simulations. Shading denotes the plus/minus one standard deviation range of individual model annual means. The gray bars at right indicate the best estimate (solid line within each bar) and the likely range assessed for the six SRES marker scenarios. Click to enlarge.
    Most of the observed increase in globally averaged temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations. Discernible human influences now extend to other aspects of climate, including ocean warming, continental-average temperatures, temperature extremes and wind patterns

  • Analysis of climate models together with constraints from observations enables an assessed likely range to be given for climate sensitivity for the first time and provides increased confidence in the understanding of the climate system response to radiative forcing.

  • For the next two decades a warming of about 0.2°C per decade is projected for a range of SRES emission scenarios. Even if the concentrations of all greenhouse gases and aerosols had been kept constant at year 2000 levels, a further warming of about 0.1°C per decade would be expected.

  • Continued greenhouse gas emissions at or above current rates would cause further warming and induce many changes in the global climate system during the 21st century that would very likely be larger than those observed during the 20th century. Best estimates for the temperature increase by 2100 in the different scenarios range from 1.8°C to 4.0°C, within broader ranges.

  • There is now higher confidence in projected patterns of warming and other regional-scale features, including changes in wind patterns, precipitation, and some aspects of extremes and of ice.

  • Anthropogenic warming and sea level rise would continue for centuries due to the timescales associated with climate processes and feedbacks, even if greenhouse gas concentrations were to be stabilized.



Lou Grinzo

Let the debates begin.

For my part, I think the IPCC is right, and if anything, this report could be underestimating the problem by not fully accounting for ice sheet melting in Greenland and Antarctica.

But of course, that won't stop people like the AEI from funding non-peer-reviewed opposition papers:,,2004399,00.html


I would be interested in seeing how they come to their conclusions. I'm hoping that the publication is freely available and well referenced. There is one item which threw me a bit:
"There is a very high confidence that the globally averaged net effect of human activities since 1750 has been one of warming, with a radiative forcing of +1.6"

I seem to remember an article from the Max Planck institute stating that increased warming through to the 1970's or 80's could be attributed to solar activity. After that period of time, the author's attributed the heating rate to human activities.


I object to the fact that this part of the report is being released before the technical portions that contain the actual underlying data and science. IMO, the scientific portions need to be released either concurrently or before the Summary for Policymakers.

That said, unlike some of my fellow conservatives, I don't think this is some Grand Liberal Conspiracy. We do need to take action on this in a way that does not ham-handedly ruin our economies. I see this as a way to increase our energy security and wean ourselves off of fossil fuels, which are finite in nature anyway.


That said, unlike some of my fellow conservatives, I don't think this is some Grand Liberal Conspiracy.

That was funny!

Anyway, as far as the timing goes they were still arguing about details earlier this week, and the full report is bound and will run ~1000 pp (and cost money), so that takes a little longer. You can argue that either they should have cut off debate earlier or put off releasing the free summary until the bound copies were ready. I don't object to the actual timing, but if they had put it off I could live with that too.


Something that worries me is that the melting of ice in the artic accelerates significatively the process of warming, as the solar radiation is not reflected back to the space, and it penetrates in the ocean water.


When is the last time Liberals organized a successful Conspiracy?

Fluoridated water in 1950's maybe?


Don't mess with my precious bodily fluids! ;)


Let’s hear it for Leftist Group Think now, but all of the computer programs tell us Global Climate Change is real! The next 100 or so years will most likely be like the last 100 years. So it’s back to that Amish lifestyle? Sorry Africa, we don't have the money or time to help you out!

Stan Peterson

I want to tell a little story.

My son was experimenting with a glass thermometer on the kitchen table, the other day when my wife started to make dinner.

It was a cold evening and the furnace was running and the house was a comfortable 70 degrees. My wife turned on the stove and the oven to make dinner.

My son was playing with his little thermometer and he rushed over to tell me the thermometer looked like it was going up.

It only registered each degree, but he thought it went up a bit to 70+ degrees maybe a quarter or half a degree. I wanted to encourage his scientific curiosity, so I said, "Please keep watching the thermometer and I'll give you a advance on your allowance later."

So off he went and triumphantly returned a half hour later to report. "Yes, I am sure that the temperature is going up", he said breathlessly. "How much?" He said "Well its still not up a degree but my thermometer shows the red line is for sure up maybe, even to almost 71 degrees". Encouraging him I said " Here is your allowance advance, keep it up."

He soon came back and said, "It still hasn't gone up a whole degree yet. but I'm even more sure and certain its almost, almost, to 71 degrees".

"Can I have another advance on my allowance?" he asked. I rewarded him as encouragement, and said to him, "See if it it goes up some more". I said to him "What will happen if this keeps up. How hot will the house get?" He went off and came back to say "It will get too hot in the house if this keeps up". I said "You are right son. I can't argue with the truth of your scientific evidence."

I then told him , "What you said is called scientific extrapolation. You took some observational measurements and then predicted what would happen".
"No one could criticize what you said. Thats how real scientists work", trying to make sure he understood the little lesson.

"But what happens if the temperature gets to 72 or 73 degrees?", I asked. He thought for a while and answered, "Nothing; it will just keep getting hotter and hotter, My thermometer says so".

I told him very good but maybe that's not the whole story.

"What can we do about it?", I asked. "Nothing, we'll cook just like the Pot Roast mom's making", he said becoming alarmed.

Then he thought for a second and said, "The only thing we could do is open the doors and windows and let the cold in". "But then we would freeze because its so cold outside!"

Then I told him about what the thermostat on the furnace does. It is there to makes sure when the temperature in the house goes up a couple of degrees, it turns off the furnace, until the house cools off, then it turns on again.

He said "Oh", and I gave him another advance on his allowance.

I'm sure he will grow up to be a Scientist or an Engineer; he certainly learned some valid scientific principles tonight. He also learned what research grants are all about, very quickly too.

My wife than said that dinner is ready and turned off the stove, and oven and served dinner. I then said, "Maybe the house was getting warmer because mom had the stove on to make dinner."

But then I told Junior, "Ill bet you never thought about that, and that the stove and oven wouldn't always be on, forever?". He said, "Gee, I never thought of that."

As we walked in to sit down to eat, I noticed that the furnace blower stopped.

Ah, the benefits of feedback and natural regulation, I thought.

But that's a story for another day when my junior scientist has grown up enough to understand, negative feedback and natural regulation. Its probably too complex for him right now.

Isn't it nice to know that the "House Warming catastrophe" has been averted?


I don't know if everyone knows this, but this is a watered down report. PRC and US delegates (anong others) pushed for more vague, and less alarming wording. The reasons for doing so include covering their policy positions, and options. A more assertive final report would likely corner them, politically.


“During past releases of the IPCC report, public attention focused on the accompanying 12-page IPCC Summary for Policymakers. This is a brief document produced through negotiation by government bureaucrats. It is neither written by nor reviewed by the scientific community and has been criticized for its promotional tone and failure to adequately communicate the complexity and uncertainty of the underlying science around climate change.”

Interesting twist, this time there will be alternative summary, prepared by “qualified experts in fields related to climate science and has been reviewed by more than 50 scientists around the world”, such as “noted climate researcher Dr. Ross McKitrick as well as Dr. Andrei Illarionov, former advisor to Russian President Vladimir Putin, Professor David Henderson, former head of Economics and Statistics at the OECD, David Bellamy, noted environmentalist”.

The report will be published on February 5, but it is already claimed to be paid by Exsson-Mobil.

As for me, I wish IPCC is right. I wish humankind is capable to influence (warm) global climate by such trivial thing as combustion of minuscule amount of carbon, sequestered in fossil fuels. For a millions years, like Swiss clockwork, Earth experienced long periods of ice age and short periods of warmth. See, for example, “ice age” or “Milankovitch cycle” at Wiki.

There are some optimistic predictions for how long current warm period will last. But most statistical and physical models suggest that we are already long overdue, and changes to ice cold will be very fast:

“It’s worth noting that in the past 430,000 years, the percentage of time that climate was as warm as it is today is quite small, about 5 to 10% ... We have basked in relative warmth for the past 12,000 years, considerably longer than the 4000- to 6000-year lengths of the previous three interglacial as seen in the Vostok ice core (3).”

James C. White, Science 2004:

I hate to think that country I live in will be wiped out from the face of Earth by advancing ice sheet of couple kilometers thick, even if I will not be around to see it.


Back one day a good while ago the us china and india talked together about something BIG.

A short time later china did something insane. They risked control of china on a mad dash for tech and inudtry. India went mad too that very same time.

Many people to this day ignore that and this the us still doesnt understand global warming.

If thats the case why is it so many things they have funded for deaces ... oddly enough have vital uses in a post global warming world?

When someone pretends to not see something as obvious as global warming one has to question if they already knew it.

If the world powers had found out about global warming in the 80s or early 90s what would they have done? Wouldnt it be what they have done?



Officially current GW movement began in summer 1988, when James Hansen, director of the Goddard Institute for Space Studies, claimed in testimony before Sen. Al Gore's Committee on Science, Technology and Space, that he was 99 percent certain that temperature had increased and that there was some greenhouse warming. For consequent quarter century the theory of man-made catastrophic global warming was extensively researched (US government, for example, spends more money on climate research than for cancer research), and findings of the scientists, actually, do not support it, or at least its “worst case scenario”. Politicians, media, buerocrats – totally different matter.

Before that, in 1970, the scare of the day was global cooling, but of course on much smaller scale.

Roger Pham

Stan Peterson,

Thanks for sharing your thoughtful and most interesting observation on the "House Warming" annecdote.
I, too, agree with you that nature has built in self-regulatory mechanism, and the earth, more than any other planets in the solar system, must have such highly-accurate system that permit the occurence of life. The water cycle and next is the carbon cycle are perhaps the most important regulatory mechanism for earth's temperature. In other heavenly bodies, there are much more extreme temperature swing, such as in the moon and in Mars, whereas Venus has always been hotter than hell, at ~800 degrees C, so swing or no swing in temperature, makes no different.

However, what human have done is altering the thermostatic setpoint of the earth, as if you or your son have discreetly turn up the thermostat temperature of your house, and the house is getting warmer and warmer,...(and of course, your son is getting happier because he is making more money out of it...kinda like Big Oil and Big Energy, ain't it? ;)

Of course, the concerned scientists, like most participants of GCC forum, are actually trying to do something about global warming...and that is in itself the earth's best self-regulatory mechanism! Don't forget that the earth has intelligent life forms, lest you forget that, and the creatures that are intelligent enough won't let global warming gets out of hand, will they?
Oh, and if the so-called intelligent life form on earth somehow fails to halt global warming of their own causing, leading to their extinction, then, eventually, over the millenium, the rate of GHG production will slowdown, and global warming will stop...and may reverse gradually in due course of geologic time frame...Another layer of the earth's "self-regulating" mechanism! Even the mighty dinosaurs went extinct, you know!

Which version of the earth self-regulatory mechanism would you rather have, Mr. Peterson?

Roger Pham

For all skeptics of global warming, I recommend you all to watch Professor Al Gore's movie "The Inconvenient Truth." 'nuff said!

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