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Ice Age Data Confirms Concerns about Future Warming

A group of climate scientists from the Potsdam Institute for Climate Impact Research (PIK) in Germany has used data from the last great Ice Age to conclude that a doubling of carbon dioxide concentration in the atmosphere would cause a global temperature increase of around 3 ºC. This is in line with previous estimates using other methods, mainly computer models.

Ice Ages are caused by changes in the Earth’s orbit, but there are multiple factors that make Ice Ages so cold, including carbon dioxide concentration. The PIK team combined modern climate models with a multitude of data about Ice Age climate to disentangle the different factors. The results are published this month in the journal Climate Dynamics.

In their study, the scientists accounted for model uncertainties by creating a set of 1,000 climate model versions—each one with a somewhat different behaviour of clouds, ocean currents or various other uncertain processes and feedbacks affecting climate. With each of these 1,000 models, a global warming scenario with doubled carbon dioxide concentration was computed.

As expected, the amount of global warming differed substantially between different model versions—as, in fact, it does between different climate models developed by different research groups.

All model versions were then tasked to simulate the climate of the last great Ice Age. Models that are too sensitive to carbon dioxide would tend to simulate an Ice Age that is too cold, and vice versa. After a careful analysis of all sources of uncertainty, the researchers concluded that a climate sensitivity of less than 1.2º C or greater than 4.3º C would be inconsistent with what we know about the great Ice Age, with the most likely value being near 3 ºC.

This assessment of climate sensitivity is a simple measure of how much climate would warm in the long run if CO2 concentration was doubled, and should not be confused with the global warming at a given time (say, the year 2100), which depends on the actual time evolution of the CO2concentration and on other climate factors.

One positive result is that we can practically rule out an extremely high climate sensitivity of six, seven or even more degrees Celsius, which some colleagues have speculated about.

—Thomas Schneider von Deimling, lead author of the study

Uncertainty about the future climatic effect of carbon dioxide emissions consists of two parts: the future carbon dioxide concentration given current levels of emissions, and the amount of warming that can be expected from a given carbon dioxide concentration.

The new PIK study addressed the second part. An earlier study from PIK published in Geophysical Research Letters looked at the first issue, also with the help of past climate data. Taking the findings of both studies together, the results suggest that current estimates of the most likely future global warming may be somewhat too low—not because the climate sensitivity has been underestimated, but because the carbon cycle could act to amplify the warming later this century.



Rafael Seidl

Note that the 3 deg C rise in average temperature refers to the long-term average. Not only does this mask local geographic variations, which may be much more severe, it also masks the fact that a sufficiently rapid period of global warming could overwhelm the systems natural damping and therefore lead to overshoot oscillations for a period of decades or centuries. That may not be much in geological time but it matters a great deal on political and economic timescales.

Moreover, despite the substantial progress made in climate modeling and prediction over the past 20 years (thanks largely to Moore's Law), it would be quite premature to assume that the above result of a probability distribution centered on 3 deg C warming is the definitive word on global warming. Uncertainties remain regarding CO2/CO3- concentrations in the oceans, cloud formation mechanisms and other critical model components. Monte Carlo approaches with paleo-climatological plausibility analyses reduce the uncertainties to some extent, but garbage in will always remain garbage out.

Furthermore, the highly non-linear nature of the equations implies that it is still entirely possible that future data points will force models to be updated and predictions to substantially change. Does that mean we can afford to simply defer action on global warming?

IMAO, no, especially since there is now a substantial body of evidence supporting the fact of global warming, even if the fraction that is anthropogenic is still a matter of debate.

The most effective approaches are probably building codes / insurance rates that encourage disaster-proof construction, architecture that limits heating and cooling effort by design and, fuel-efficient vehicles and commute strategies.

allen Z

Bingo. There are a few other points not addressed here. The Sun might just fluctuate 0.1%, but that means 1 watt per sq meter multiplied over the sun facing surface entire earth (with some normal deflection due to angle of the sun on the surface and ice/snow, ie. arctic). Another is global dimming, which itself may threaten to wreak havok on global monsoon systems. It may also mask GHG effects, making it cooler than otherwise.
___We, the West, cleaned up the particulates/acid from our smokestacks and tailpipes from the 70's-present. The USSR collapsed, and with it their worst most inefficient factories, and their associated emissions. With continuing, and growing, GHG output with less dimming pollutants, the past 15 yrs have seen a marked rise in average global temp. However, this will be muddled by the growing developing economies, namely the PRC and India. Enormous quantities of fossil energy, esp coal, have been consumed w/out modern pollution controls. Never mind the GHGs, the particulates/ aerosols and acid rain/ocean acidification will mask the warming and damage CO2 absorbing/converting plants, coral, etc. When the particulates are removed for aesthetic/political/health/economic reasons, the GHGs will be unleashed.
_The Arctic ocean icecap might quickly shrink, though some effects will mitigated by the fact that water reflects light better at low angles than at 90 degrees, ie more than 80 degrees from vertical. However, with the ice gone, the wave action on Arctic permafrost shores will increase. This may be the mechanism in which large quantities of methane gas hydrates and CO2 buried under/in the permafrost gets released. With more GHGs in the atmosphere, the warming increases. As the climate gets warmer, more ice and permafrost melt, releasing even more GHGs and raising the sea level. As the sea level goes up, more low lying arctic land is inundated with seawater. The seawater melts the permafrost faster like salt on an icecube. More erosion happens, and all the while more GHGs are released through melting permafrost. It may get out of hand very quickly.
___Another is the normal planterary fluctuations might mask or exacerbate the warming too. Remember the end of the last active Atlantic hurricane (AMO) period coincided with a cold decade (1970's). The one before was similar (1900's). If extrapolated, we might expect another in the 2030's. This might lull many into believing global warming is void. It might also cause 10-20 yrs of debate and inaction due to squabbling over what is happening to the climate. That is time we might not have.
___One possibility is sequestation. However, there are many forms of this. Some of it is being done to pressurize the crude oil (think pop soda) left in after secondary recovery methods are no longer working. Others are straight inject back into the ground. One way would be to produce large quantites of algae. Use some of it to fuel/feed/equipt our economies/societies/ countries, and the rest we can bury in deep offshore sedimentation zones.
_Heck, Maritania has enough seashore, land, and sun to do this and run/grow their economy on carbon credits, fuel, feed, and chemicals. However, they would need to have an agreement with Brazil, Venezuela, or Bangladesh for the right to sequester carbon offshore of the mighty river mouths.
___As noted above by Seidl, efficiency and common sense will be much needed. I would add carpooling, as well as rapid mass transit.
_5 people in a SUV getting 15mpg per trip is in fact getting 75mpg/person. Better yet, a diesel Mazda 5 with 6 aboard with an average of 30mpg is getting 180mpg s person. Even better would be 4 in a subcompact with 60mpg, which calculates to 240mpg/person.
_With subways, the issue is time. With all the stops, express lines (3 or 4 tracks) shortened the ride. However, there is still a point in which it takes more than 1:35 to go from home to work, and people will drive to work. Adding a 5th and/or 6th (superexpress), while taking shortcuts, having fewer stops, and high speed curves/switches will speed the passenger along. In NYC, this will benefit those west of the Van Wyck Expressway (I-678) and the Rockaways in Queens, parts of northeastern and eastern Bronx, eastern and southern Brooklyn, and the whole Staten Island (if a line can hook up to a revamped SIRT, after a tunnel crossing of the Narrows or Upper New York Bay).
___London, and most other mass transit systems, do not have widespread express lines for subways/light rail. They might benefit too, but will be expensive to build (the 2nd Ave Line calculates to a whopping 1+ billion dollars a mile for 2 parallel local tracks). I do not know how much it will cost in Europe, South America, or Asia.

allen Z

...EAST of the Van Wyck Expressway (I-687)...


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