Posted on 06/22/2006 8:28:41 AM PDT by Semus Dynnen
Study Says Earth's Temp at 400-Year High Jun 22 11:10 AM US/Eastern
By JOHN HEILPRIN Associated Press Writer
WASHINGTON
The Earth is the hottest it has been in at least 400 years, probably even longer. The National Academy of Sciences, reaching that conclusion in a broad review of scientific work requested by Congress, reported Thursday that the "recent warmth is unprecedented for at least the last 400 years and potentially the last several millennia."
A panel of top climate scientists told lawmakers that the Earth is running a fever and that "human activities are responsible for much of the recent warming." Their 155-page report said average global surface temperatures in the Northern Hemisphere rose about 1 degree during the 20th century.
The report was requested in November by the chairman of the House Science Committee, Rep. Sherwood Boehlert, R-N.Y., to address naysayers who question whether global warming is a major threat.
Last year, when the House Energy and Commerce Committee chairman, Rep. Joe Barton, R-Texas, launched an investigation of three climate scientists, Boehlert said Barton should try to learn from scientists, not intimidate them.
The Bush administration also has maintained that the threat is not severe enough to warrant new pollution controls that the White House says would have cost 5 million Americans their jobs.
Climate scientists Michael Mann, Raymond Bradley and Malcolm Hughes had concluded the Northern Hemisphere was the warmest it has been in 2,000 years. Their research was known as the "hockey-stick" graphic because it compared the sharp curve of the hockey blade to the recent uptick in temperatures and the stick's long shaft to centuries of previous climate stability.
The National Academy scientists concluded that the Mann-Bradley-Hughes research from the late 1990s was "likely" to be true, said John "Mike" Wallace, an atmospheric sciences professor at the University of Washington and a panel member. The conclusions from the '90s research "are very close to being right" and are supported by even more recent data, Wallace said.
The panel looked at how other scientists reconstructed the Earth's temperatures going back thousands of years, before there was data from modern scientific instruments.
For all but the most recent 150 years, the academy scientists relied on "proxy" evidence from tree rings, corals, glaciers and ice cores, cave deposits, ocean and lake sediments, boreholes and other sources. They also examined indirect records such as paintings of glaciers in the Alps.
Combining that information gave the panel "a high level of confidence that the last few decades of the 20th century were warmer than any comparable period in the last 400 years," the academy said.
Overall, the panel agreed that the warming in the last few decades of the 20th century was unprecedented over the last 1,000 years, though relatively warm conditions persisted around the year 1000, followed by a "Little Ice Age" from about 1500 to 1850.
The scientists said they had less confidence in the evidence of temperatures before 1600. But they considered it reliable enough to conclude there were sharp spikes in carbon dioxide and methane, the two major "greenhouse" gases blamed for trapping heat in the atmosphere, beginning in the 20th century, after remaining fairly level for 12,000 years.
Between 1 A.D. and 1850, volcanic eruptions and solar fluctuations were the main causes of changes in greenhouse gas levels. But those temperature changes "were much less pronounced than the warming due to greenhouse gas" levels by pollution since the mid-19th century, it said.
The National Academy of Sciences is a private organization chartered by Congress to advise the government of scientific matters.
Study: Earth likely hottest in 2,000 years
It has been 2,000 years and possibly much longer since the Earth has reached such high temperatures, according to the National Academy of Sciences. They told lawmakers Thursday the Earth is running a fever and "human activities are responsible for much of the recent warming."
The above is the headliner on CNN.com
I thought water vapor was the chief climate determinant in the atmosphere?
The Role of the Sun in 20th Century Climate Change
"Estimates of Northern hemisphere surface temperatures from 1610 to 1800--during part of the so-called Little Ice Age--correlate well with a reconstruction of changes in solar total radiation--around the time of the Maunder Minimum (Fig. 2c). This suggests, without proving, a predominant solar influence on climate throughout this 200 year, pre-industrial epoch. The reconstructions of solar radiation and surface temperature shown for these years in Figures 3a and 3d tell of an increase in solar radiation of 0.14 percent and a coincident warming of 0.28°C. If we apply the same implied sensitivity to the period since 1850, the 0.13 percent increase in solar radiation in the last 140 years should have produced a warming of 0.26°C, or about half of that observed. If we apply the same relationship to the last 25 years, solar changes can account for less than a third of the warming observed (Fig. 5)."
And what exactly caused the lack of heat from sunlight for the entire period of the Little Ice Age?
Reduced solar activity, indicated by lack of sunspots.
Water vapor (relative humidity) responds to changes in radiative forcing. CO2 is the main atmospheric constituent that changes Earth's radiative balance. If increasing CO2 concentration causes the Earth to warm, relative humidity should increase, accentuating the warming. (Increasing cloud cover might counter some or all of the expected warming, or could even augment it more.)
I presume you mean that increasing clouds would reflect radiation back into space (cooler earth) and trap what gets through (warmer earth). So we don't know which effect is going to predominate.
exactly right
Paleotemperature reconstructions and climate models are not the same thing. I would read the links to better characterize the arguments; the RealClimate side is emphasizing that they acknowledged the uncertainties of their pre-1600 reconstruction. Nonetheless, the hockey stick presented by the IPCC made it seem certain that the 1900s were the warmest period of the past 1,000 years. That's not certain.
What is critical is whether or not the current warming trend is related to human activities (some of the warming probably is); if so, how much is caused by human activities (still working on it); and how much faster the expected rate of change will be compared to natural climate variability ups-and-downs (as the Panel says, that needs more research).
But if you have more than anecdotal evidence or speculation that people cause global warming I would be happy to see it.
The certainty is that the increase in atmospheric CO2 since 1850, 80 ppm higher than the highest natural CO2 concentration observed in the past 640,000 years (ice core data) is due to human activities. Increasing CO2 concentration will change Earth's radiative balance such that, with all other quantities held constant, global temperature would increase. The problem is that all other quantities are not constant, so determining how much warming is clearly human-caused is difficult. Climate feedbacks in response to CO2 radiative forcing can be positive or negative. It appears that the balance sheet will favor the positive side of feedback, augmenting the warming due to CO2, but that is not in any sense definitive.
Right.
So are they attempting to say that the Earth's temperature never fluctuates? Naturally. On it's own?
I'm glad we agree.
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So much to worry about...
I appreciate your attempt at interpretation of the NAS report. At present I remain skeptical of the results.
The main reason for my skepticism is due to the political nature of the issue. A position has been taken and now considerable time, energy, money and political capital has been devoted to justifying that position. Those who remain outside the politically-correct envelope and may be critical of the process are ostracized, threatened with loss of position and funding or both. This leads to compromise of the integrity of the results.
Though interested and somewhat familiar in this area myself, I do not have the time or inclination to try to perform an independent review of the results. I will leave that to others degreed in the field. However, the process has become so heated and politically controversial with possible life-style changing impacts for those of us in the first world, that any conclusions must be reviewed with great detail to determinate their probability and accuracy.
If you can't even get this right, then how can anyone believe any other assertions/assumptions you put forth.
The chief climate change agent in the atmosphere is water vapor. CO2 is but a tiny fraction of water vapor. Therefore, small changes in water vapor can make large changes in the climate, much larger changes than even exponetial CO2 changes. It has also been proven that CO2 levels follow warming changes, not preceed them. If CO2 is indeed an indicator of warming, then it is only an indicator that the change has already taken place and CO2 is not the cause of the change.
Pull yer head outa yer lower sphincter and try to actually do what your screen name indicates. Go suck up to Michael Mann and friends, you won't find any here naive enough to fall for your prevarication and wholly ignorant assumptions/assertions.
Sheesh, watta maroon!
Next you'll probably be asserting that the tree rings on Mars prove that the industrial revolution fueled by the little green men there is causing the melting of the polar icecaps on that planet. And then you'll probably come up with some Venusian and Uranian-centric cause for the warming of those planets too. Jeeeeez, then I suppose the Plutonians driving SUV's are responsible for that planet's warming and increasing atmospheric pressure.
Yeah, that's the ticket. It was all started by those nasty humans populating this speck of dirt. Now I got it!
I'm not sure what you mean by flawed climate models. Climate models are investigative tools, since we can't experiment with other Earths to see what happens to climate. The basic atmospheric CO2 effect on Earth's radiative balance is not speculation; there is a reason based on basic physics that CO2 is called a greenhouse gas.
So why risk an entire planets economy for a theory that can't be anywhere near proved?
Because ignoring what could happen while waiting for definitive proof could be dangerous. But note that I'm not favoring risking an entire planet's economy: the world's (particularly developed countries) economic dependence on fossil fuels is already doing that. If you don't believe me, examine the scenarios related to a successful terrorist strike on Saudi Arabia's main oil production facility.
You apparently know a lot more than I about "global warming".
Possibly.
I believe that the earth is warming. I don't think it has anything to do with people. If it does, the consensus is that nothing can be done by people to stop it.
Relative to my earlier comment, and a posting I just made about the prospects for cellulosic ethanol, what can be done about it is to change the way we produce and use energy. There are MAJOR reasons that this is a good idea, and the positive effects for climate are about sixth on the list. But if we change the way society produces and uses energy, something will have been done about climate, and the economy will probably be safer too.
So why waste resources better used elsewhere to attack a problem that cannot be affected by any reasonable efforts?
I'd prefer to focus our resources on strategies that will be beneficial and effective.
But what you quoted sited an increase in solar radiation and temperature.
The reconstructions of solar radiation and surface temperature shown for these years in Figures 3a and 3d tell of an increase in solar radiation of 0.14 percent and a coincident warming of 0.28°C.
What am I missing here?
Not that it matters as I happen to believe that global warming can be a good thing.
Not to mention we worked so hard to overcome global cooling in the '70s.
It has also been proven that CO2 levels follow warming changes, not preceed them.
In glacial-interglacial cycles, the temperature increase or decrease at the beginning of either an interglacial or glacial is likely driven by Milankovitch forcing. The subsequent climate response appears to be amplified by atmospheric CO2.
There's a nice article about this on Real Climate, but the site is having problems (probably a lot of traffic today).
Next you'll probably be asserting that the tree rings on Mars prove that the industrial revolution fueled by the little green men there is causing the melting of the polar icecaps on that planet.
All name-calling aside, there's also an article at RealClimate that discusses this, and explains why the observations of change in the South Pole ice cap on Mars are a regional climate change, augmented by dust levels in the atmosphere. The article is entitled "Global Warming on Mars?" and I've linked to it numerous times. A Google search with the exact phrase will probably find it, but as I noted, RealClimate is suffering today
(in more ways than one; the panel report indicated quite a few problems with the paleoclimate reconstruction methodologies. How's that for sucking up to Dr. Mann?)
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