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Study Concludes 10 More Years of Business-as-Usual CO2 Emissions Could Make Avoiding Dangerous Climate Change Impossible

30 May 2007

An additional 10 years of continued rapid growth of CO2 emissions and infrastructure may make avoiding dangerous climate change “impractical, if not impossible”, according to a recently published study in the journal Atmospheric Chemistry and Physics.

The lead author of the study is James Hansen, Director of NASA’s Goddard Institute for Space Studies (GISS) in New York. Forty-six other researchers from other organizations in the US and France also contributed to the work. The researchers used data from earlier warm periods in the Earth’s history to estimate climate impacts as a function of global temperature, climate models to simulate global warming, and satellite data to verify ongoing changes.

Although identifying “dangerous” effects is “partly subjective”, the report concludes that additional global warming of more than 1°C above the level in 2000 will have effects that may be highly disruptive, and push the climate past tipping points.

Tipping points can occur during climate change when the climate reaches a state such that strong amplifying feedbacks are activated by only moderate additional warming. This study finds that global warming of 0.6°C in the past 30 years has been driven mainly by increasing greenhouse gases, and only moderate additional climate forcing is likely to set in motion disintegration of the West Antarctic ice sheet and Arctic sea ice. Amplifying feedbacks include increased absorption of sunlight as melting exposes darker surfaces and speedup of iceberg discharge as the warming ocean melts ice shelves that otherwise inhibit ice flow.

Have we already passed a “tipping point” such that it is now impossible to avoid “dangerous” climate change? In our estimation, we must be close to such a point, but we may not have passed it yet. It is still feasible to achieve a scenario that keeps additional global warming under 1°C, yielding a degree of climate change that is quantitatively and qualitatively different than under BAU scenarios.

The researchers conclude that a CO2 level exceeding about 450 ppm would be dangerous. The current atmospheric concentration of CO2 is currently 383 ppm, up from 280 ppm at the start of the industrial age. Atmospheric carbon is currently increasing at about 2 ppm per year.

The study also shows that the reduction of non-carbon dioxide forcings such as methane and black soot can offset some CO2 increase, but only to a limited extent.

The team used a computer model developed by the Goddard Institute to simulate climate from 1880 through today. The model included a more comprehensive set of natural and human-made climate forcings than previous studies, including changes in solar radiation, volcanic particles, human-made greenhouse gases, fine particles such as soot, the effect of the particles on clouds and land use. Extensive evaluation of the model’s ability to simulate climate change is contained in a companion paper to be published in Climate Dynamics.

The authors use the model for climate simulations of the 21st century using both business-as-usual growth of greenhouse gas emissions and an alternative scenario in which emissions decrease slowly in the next few decades and then rapidly to achieve stabilization of atmospheric CO2 amount by the end of the century. Climate changes are so large with business-as-usual, with additional global warming of 2-3°C (3.6-5.4°F) that Hansen concludes “business-as-usual would be a guarantee of global and regional disasters.”

However, the study finds much less severe climate change—one-quarter to one-third that of the business-as-usual scenario—when greenhouse gas emissions follow the alternative scenario.

A scenario that avoids “dangerous” climate change appears to be still technically feasible.

Our conclusion that global temperature is nearing the level of dangerous climate effects implies that little time remains to achieve the international cooperation needed to avoid widespread undesirable consequences. CO2 emissions are the critical issue, because a substantial fraction of these emissions remain in the atmosphere “forever”, for practical purposes. The principal implication is that avoidance of dangerous climate change requires the bulk of coal and unconventional fossil fuel resources to be exploited only under condition that CO2 emissions are captured and sequestered.

A second inference is that remaining gas and oil resources must be husbanded, so that their role in critical functions such as mobile fuels can be stretched until acceptable alternatives are available, thus avoiding a need to squeeze such fuels from unconventional and environmentally damaging sources. The task is to achieve a transition to clean carbon-free energy sources, which are essential on the long run, without pushing the climate system beyond a level where disastrous irreversible effects become inevitable.

Separately, a different new study by NASA scientists suggests that business-as-usual greenhouse-gas warming may raise average summer temperatures in the eastern United States nearly 10° Fahrenheit by the 2080s. It also suggests that current climate models are underestimating surface temperature changes.

The research found that eastern US summer daily high temperatures that currently average in the low-to-mid-80s (degrees Fahrenheit) will most likely soar into the low-to-mid-90s during typical summers by the 2080s. In extreme seasons—when precipitation falls infrequently—July and August daily high temperatures could average between 100 and 110 degrees Fahrenheit in cities such as Chicago, Washington, and Atlanta.

To reach their conclusions, the researchers analyzed nearly 30 years of observational temperature and precipitation data and also used computer model simulations that considered soil, atmospheric, and oceanic conditions and projected changes in greenhouse gases. The simulations were produced using a widely-used weather prediction model coupled to a global climate model developed by NASA’s Goddard Institute for Space Studies.

The global model, one of the models used in the recently issued climate report by the Intergovernmental Panel on Climate Change (IPCC), was utilized in this study to identify future changes in large-scale atmospheric circulation patterns due to the build up of greenhouse gases. This information was then fed into the weather prediction model to forecast summer-to-summer temperature variability in the eastern United States during the 2080s. The weather model showed that extreme summertime surface temperatures developed when carbon dioxide emissions were assumed to continue to increase about two percent a year, the “business as usual” scenario. These findings are too recent to be included in the latest IPCC report.

The weather prediction model used in this research is advantageous because it assesses details about future climate at a smaller geographic scale than global models, providing reliable simulations not only on the amounts of summer precipitation, but also on its frequency and timing. This is an important capability for predicting summer temperatures because observed daily temperatures are usually higher on rainless days and when precipitation falls less frequently than normal.

The study determined that the global climate model (GCM) likely underestimates future air temperatures near the ground because it simulates too many rainy days on which clouds block sunlight and on which the wet ground is additionally cooled by evaporation. Statistics of rain frequency inherently depend on the size of the area being monitored, since it rains more often somewhere within a large area than somewhere within a much smaller area. The smaller area of the weather prediction model provided better tuning.

However, even accounting for the relatively large area of the GCM's computational elements, the NASA researchers found that the GCM still overestimates precipitation frequency. By comparison, the corresponding percentage of rainy days predicted by the regional mesoscale model for the same summers was lower and much more realistic.

The scientific literature indicates that other GCMs are also flawed by computations of too frequent precipitation and unrealistic morning showery precipitation. We are not aware of any other study that has documented the impact of the precipitation simulation imperfections on GCMs’ predictions of surface air temperature, but the ability of such flawed models to predict global warming and its extremes could be compromised. This study suggests that climate change will cause more extreme temperatures than implied by previous GCM studies.

(A hat-tip to Marcus!)


May 30, 2007 in Climate Change | Permalink | Comments (144) | TrackBack (0)


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The purveyors of ICEs are not going to listen to this warning. They are driven by the profit motive not the welfare of either man or the planet. What is sad is that the public could simply quite buying new ICE products and force a change; but, I fear they are victims of slick advertising and short sightedness.

I would like to suggest those who comment on this website extend your Green Car Congress knowledge to the local papers, your government representatives and your friends. Every time you get a chance to comment do so. I think educating people as to the real truth about the continued use of ICEs might give us a chance to reverse the buildup of GHGs.

What TOTAL B.S. Lets just guess and start making things up. We might have to look at the Sun to understand why the earth warms up or cools down.
We are all made of Carbon. Human CO2 does not have the ability to increase global temps.
Please do not look into B.S. claims and buy the snake oil before you leave.

Evil Human

I had a feeling this article might make some people's brains short circuit. Guess I was right.

DENIAL- It's a great defense mechanism that helps us cope as human beings. Too bad we're coping at the cost of our children's future...

I guess we have our work cut out for us, don't we? Creating any kind of international consensus is like herding some very large, well-armed cats. It took over ten years work out the details of the Kyoto Accord and get that going. I remember the initial discussions started about 1992, the basics were agreed to five years later, and of course the treaty only went into effect in 2005. It's had dubious success since then.

That said, I think that peak oil will preclude any "Business as Usual" scenario.

I hope the green freaktards are right, I invest in hybrid batteries. LOFL
These tards can poin to zero tangible damage estimates ever coming true, much less the end of the world in 10ys.
But please do tell your friends and neighbors to buy hybids be they sedans or suv's.

Umm WTF, only 10 years left, an UK report said it's only five years before it was to late. But the computer models are never wrong are they now? BS In! = BS Out! And I thought the Marxists had all died off after the death of the USSR? Welcome back REDS!!! Oh, please just keep pushing the green technology fix it because I’ve made lots of money off it.

More short circuits happening....hopefully there will be a full meltdown.

Isn't it amazing how the blues look at green and see red. It must be some kind of unreality filter.

Cervus: I think you might be right ... 10 more years of increasing production ... maybe. 10 more years of any production increase outstripping demand if business as usual ... I don't think so.

Peak Oil just means more coal.

Nah, there wont be business as usual of course, tornadoes and taufan will destroy a part of the civilisation while floods and droughts take care the rest. The nature has a way to release its pressure.

So time to have some take-bus/bike-to-work-and-plant-a-tree campaign?

Fidel Castro and Chavez are so happy when they see the liberals (Marxists) trying to destroy the USA from within.
I think Chavez will come to the US by crossing the mexican border then become a democratic Presidential candidate for 2008. So get ready you are asking for it.
Only 10 years left.

It is indeed a full moon!

Hansen is one of the most respected climatologists in the business. He knows whereof he speaks and ought not to be dismissed by labeling him a red or other name calling.

The US is the biggest emitter of CO2 both in absolute terms and per capita. If the government would be proactive on addressing global warming rather than reactionary and trying to seize more oil we might have a chance at avoiding a real calamity but it doesn't look like that will happen at least until the next election.

Calculate from physical model max greenhouse effect of CO2. Assume all heating in 20 century happened because of GHG effect (throw away atmosphere heating due to two Pacific Decadal Oscillation heating and only one cooling events of 20 century, and record high solar activity) and calibrate to it CO2 climate sensitivity to obtain max value. Apply calculated max CO2 sensitivity to crude climate model, throwing away convection cooling (major mechanism of surface cooling short-circuiting all GHG effects), and throw away cooling effects of clouds. Multiply calculated GHG effect by factor of three due to unquantified positive feedback of water vapors. Throw away ANY possible negative feedbacks. Tune the model by artificial coefficients to conform to observed temperatures (use unquantified effects like aerosol cooling when it is necessary to explain, say, 1940-1977 cooling, and neglect aerosols everafter). Make sure it produces catatastrophic heating in near future. Make sensational predictions, scare the public, get another mega dollars funding . In couple of years adjust diverging models to conform to new temperature data. REPEAT.

And never mention that “450 million years ago, CO2 levels were over 4,000 ppm (more than 10 times today’s level) yet the earth went through an extended ice age period”.

This is how AGW models are created and working.

I tend to pay attention to observations rather than models, really. And the observational data is worrying. But we need to make sure that we don't engage in "climate porn". Alarmist rhetoric evokes irrational actions. That helps nobody.

Alarmist rhetoric evokes irrational actions.

And in the next breath, "The economy will collapse if we adopt Kyoto!"

Andrey, you know I keep wondering, seeing as thow you seem to know a few tid bits about this and that, why you haven't written a scientific paper disputing climate change. Now why might that be.....

Andrey, you know I keep wondering, seeing as thow you seem to know a few tid bits about this and that, why you haven't written a scientific paper disputing climate change. Now why might that be.....

Because there's a global conspiracy to drown out voices like his, because, uh, scientists are making billions by crying wolf, and uh, the UN is out to get us all with black helicopters, and uh...


Don't put words in my mouth. You can agree that something must be done but disagree that the Kyoto Protocol is an effective policy.

Don't put words in my mouth.

Would you like a quote of yourself? I found this with a simple search that took 5 seconds.

"And if this legislation does end up harming California's economy, will its proponents take responsiblity for that harm?"

You're an alarmist who is complaining about alarmism. I wonder when the irony of that will dawn on you.

You can agree that something must be done but disagree that the Kyoto Protocol is an effective policy.

That has nothing to do with anything. You can't decry alarmism while being an alarmist. Well, you can, but then no one will take you seriously.


I'll own up to that statement. But that was months ago and I had rather different views then. I've reexamined my own rhetoric, I've reexamined my position on climate change, I've reexamined my opposition to a carbon tax. That kind of self-reflection is never easy.

It's curious you're hiding behind a Anon name, though. I'll own up to what I said. Will you own up to this?

I sometimes wonder if finite fossil fuels is not the lord's little cosmic joke. We will run out of fuel before we completely alter the climate on the planet.


Take a look at last update of global temperatures measured by satellites, produced by same James Hansen, the director of NASA's Goddard Institute for Space Studies:

Note that measurements began at 1978, after 1940-1977 cooling. Peak of 1997 is due to severe El Nino event. Then take a look at PDO at Wiki:

How alarming it is, decide for yourself.


Do you have another resource than I still visit Climate Audit on occasion, and Nature's new Climate Feedback blog. But Miloy isn't really credible.

Andrey is conveniently ignoring the well-founded theoretical expectation that the Sun has brightened by about 1/3 over its lifetime, so 450 Myears ago it was about 3% dimmer than it is now. Nevertheless the Earth has been warm enough over most if not all of its history to sustain liquid water on its surface, because of (wait for it)... variable greenhouse effect! Look for references to the "faint young Sun paradox". And now humans are adding greenhouse gasses, enough so that we are preventing what would otherwise soon be a new ice age.

Laugh while you can, monkey boys. Unload any south Florida property sooner rather than later.

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