The understanding of anthropogenic warming and cooling influences on climate has improved since the Third Assessment Report (TAR), leading to very high confidence that the globally averaged net effect of human activities since 1750 has been one of warming, with 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.
As predicted, human actions have "more likely than not" caused increases in intensity of tropical cyclones (hurricanes and typhoons). That means that expert opinion places the likelihood of that above 50% and below 2/3. The future trend is considered "likely," which means between 2/3 and 90% likelihood.
A decrease in unusually cold days and an increase in unusually hot ones is virtually certain (greater than 99%), and the likelihood that humans have already caused such changes is likely.
The report also increased the confidence in paleoclimate estimates (including the data surrounding the "hockey-stick"):
Paleoclimate information supports the interpretation that the warmth of the last half century is unusual in at least the previous 1300 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 metres of sea level rise.
The previous report only went back 1000 years.
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. This is an advance since the TAR’s conclusion that “most of the observed warming over the last 50 years is likely to have been due to the increase in greenhouse gas concentrations”. Discernible human influences now extend to other aspects of climate, including ocean warming, continental-average temperatures, temperature extremes and wind patterns.
This statement is stronger than previous estimates. It is worth noting that few, if any, of the statements in this report are weaker than previous reports. The evidence is only moving in one direction.
Not only is it increasingly clear that human actions have increased temperatures, we haven't even seen the full effect:
It is likely that increases in greenhouse gas concentrations alone would have caused more warming than observed because volcanic and anthropogenic aerosols have offset some warming that would otherwise have taken place.
And contrary to what climate change deniers have claimed:
The observed widespread warming of the atmosphere and ocean, together with ice mass loss, support the conclusion that it is extremely unlikely that global climate change of the past fifty years can be explained without external forcing, and very likely that it is not due to known natural causes alone.
"Extremely unlikely" means less than 5% chance, very unlikely is less than 10%.
If carbon dioxide concentrations double, average temperatures are expected to rise between 2 and 4.5 degrees Celsius, or 3.6 to 8.1 degrees Fahrenheit.
The report also indicates that even under the most optimistic scenario for the future, we are likely to see substantial warming over the next century. The yellow line would involve maintaining carbon dioxode concentrations at current levels, a task presently impossible. The difference between scenarios in which society moves to cleaner technologies quickly is substantially cooler than the scenario in which business proceeds as usual.
It is also worth noting that all models project a substantial warming of the central parts of North America, and little change in precipitation for this area.
Just checking, are you taking those graphs from the IPCC report?
Because there was a quite strange op-ed in the New York Sun this morning claiming that the IPCC report was some kind of massive victory for global warming skeptics, and one of their big supports were that:
the "the Hockeystick, a graph that purportedly illustrated that the 20th century was "unusually warm."... does not appear in the summary
I'm not sure what is proven by analyzing what graphs the IPCC didn't include a graph, but I was just thinking it would be pretty funny if the Sun printed that and then it turns out the hockeystick-looking graph at the top of this page was in the report after all.
The figures here are indeed from the IPCC SPM. The hockey-stick itself isn't there, but the report does strengthen the conclusion drawn from that one graph, extending it over a longer term. The first figure here shows CO2, which never generated as much debate.
The argument over that hockey-stick graph was always silly, but arguing about which graphics will appear in the SPM is even worse.
"human actions have "more than likely" caused increases in intensity of tropical cyclones (hurricanes and typhoons). That means that expert opinion places the likelihood of that above 50% and below 2/3. The future trend is considered "likely," which means between 2/3 and 90% likelihood."
Huh? Is this right? "More than likely" is less probable than "likely" based on that sentence. Or are the two switched?
The new IPCC report does not appear to point to any research that reconciles data which shows during periods of extensive continental glaciation across the Phanerozoic there have been significantly higher levels of atmospheric CO2 compared to current levels. Some research estimates the difference as high as much as 16 times current level. Please reference any of the sections that provide comments for this issue?
Markk, I'm a moron. I wrote "more than likely" when I should have written "more likely than not." Must fix.
Daprez, this is a "summary for policymakers," not the full report. That full report will not be issued for several months, and will focus on modern climate. The discussion on paleoclimate focuses on the Holocene, not the whole of the last 500 million years. There are many factors that drive climate change, including the Milankovich cycles, all of which could drive glaciation at different times.
Right now, carbon dioxide concentrations are driving climate change.
Once again I must ask for the empirical research that shows how a gas at the current trace concentration levels of atmospheric C02 is unequivocally shown to be the key driver in climate change. There are so many other factors that have a much stronger effect on climate that are getting pushed aside by the policy debate when the science is still has a lot of work to do. The issue of climate change must look at all time periods for understanding drivers and climatic effects. Limiting the science to only the last 11,000 years of climate is just plain daffy.
Daprez, there is no scientific dispute about the warming effects of carbon dioxide. Doubling the amount of it will double its heating effect, all else being equal.
Trying to compare temperatures millions of years ago, under who knows what atmospheric conditions and when the Earth's angle to the sun was different, as was its distance to the Sun, is what's daffy. Over millions of years, solar irradiance changes, volcanic activity changes, and the flow of the oceans changed, altering the flow of heat from the equator to the poles. Making that comparison is absolutely irresponsible, and scientifically meaningless.
The upshot of the IPCC report is that, while other factors are definitely at work in the climate, it is "extremely unlikely that global climate change of the past fifty years can be explained without external forcing, and very likely that it is not due to known natural causes alone." Moreover, "[m]ost 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."
We'll have the full reports in a few months, and you can assess the degree to which "The understanding of anthropogenic warming and cooling influences on climate has improved since the Third Assessment Report."
Sure "Doubling the amount of it will double its heating effect." But what is the level of that heating effect? That's the research in question. In my opinion, that research is curiously lacking.
Looking at the history of the planet helps us understand how different levels of CO2 may effect the climate. You say that "Making that comparison is absolutely irresponsible, and scientifically meaningless." There are many scientist that do not agree with you in this point and see it as an essential to the question. The geologic record shows an enormous expanse of time that we can investigate to determine climatic drivers. Many eras are very similar to the Holocene. Let's use them too.
It looks like now studying the Holocene isn't so "daffy."
I'm not arguing against looking at the whole history of the world, I'm just saying that it's irresponsible to look at only temperature and carbon dioxide when you acknowledge that there have been other factors at work over the last 550 million years, many of which would not be relevant over the shorter scale of the Holocene.
Here's a discussion of the effects of changes in ocean flow as a result of plate tectonics. Over millions of years, these effects are major, but not over a span of 50 years. The only time frame in which we have data that could address changes of carbon dioxide concentrations and temperature over 150 years is the Holocene, and really only the last thousand or so.
I am well aware of the role that plate tectonics can play as a climate control over several hundred million years. You seem to be playing that card to confuse the issue. The tectonic effects on climate become less and less throughout the Cenzoic compared to modernity because the plate configurations are not dissimiliar to the modern era. You are saying that the only time frame with sufficient data and which is relevant for understanding carbon dioxide effect on the climate is the Holocene. This is not true and totally biases an analytical approach. Much of the Cenozoic is worthy of close examination and is relevant to understanding the modern climate. The IPCC, by limiting focus on the Holocene, is adding a definite bias that does not require the climate models, cited by the IPCC, to account for periods like the Pliocene and Miocene which had carbon dioxide levels in the range of 800 to 1000 ppm simultaneous with long periods of cold climates. Tectonics and Milankovitch together cannot account for the amount of cooling together with the high levels of carbon dioxide. More work is needed to answer questions about why these periods in the Tertiary stand in contrast to the hypothesis that the modern climate is changing because of people. It would be nice to not have to deal with those issues and it appears that the IPCC is doing just so they can continue the doomsday drumbeat.
"Tectonics and Milankovitch together cannot account for the amount of cooling together with the high levels of carbon dioxide."
Do you have a citation for that claim?
You say that my mention of tectonics is intended "to confuse the issue," but I think the same of your dredging up climate 500 million years ago or even 20 million years ago. Extraterrestrial impacts, periods of intense volcanic activity, tectonic effects, Milankovitch cycles, changes in solar activity and many other factors come into play over millions of years but do not enter the issue of current forcings on the climate.
For instance, the isthmus of Panama didn't close until about 15 million years ago, and that closing had dramatic global consequences. Shifts in Antarctica's position during the Cenozoic also changed its ability to sustain icecaps, and icecaps have a positive feedback with cooling.
Seems like that is worth considering. Again, a citation of where this critique comes from would be helpful, since you've already shifted goalposts from the entire Phanerozoic down to the Cenozoic without comment.
No goal post shifting here Josh... You want and the IPCC want to limit the focus on the Holocene. There is so much more information that is pertinent to the debate throughout the Phanerozoic, especially in the Cenozoic. The issue seems to be that the information available across the span of even 20 million years doesn't seem to gel as well with the current Global Warming hypothesis supported by the IPCC using only the last 11,400 years. Why else disregard a volume of data that considers over 3 orders of magnitude more time?
For an excellent reference in this area please consider reading "Geological Perspectives of Global Climate Change," edited by Gerhard, L. C., Harrison, W. E., and Hanson, B. M., 2001, American Association of Petroleum Geologists in collaboration with the Kansas Geological Survey and the AAPG Division of Environmental Geosciences, AAPG Studies in Geology #47, 327 p., US$ 49.00, ISBN# 0-89181-054-4.
On a different note... this is a very disturbing development that seems to signify how rabid the politics surrounding the dramatization that is "Global Warming." Thanks Al...
Silence the critics...errr... heretics!
First, the CNS story is inaccurate. The guy isn't getting fired, the governor just objects to the university giving him a title that implies he represents the State of Oregon's positions. He isn't being fired, just given a new title.
Second, I would really like a specific citation to a particular paper or chapter which explains what you meant when you wrote "Tectonics and Milankovitch together cannot account for the amount of cooling together with the high levels of carbon dioxide." I can't respond to such a specific claim without some context on the basis for the judgment.
Third, I am not shifting goalposts. You started off talking about changes across the Phanerozoic. I pointed out that the earth has undergone major changes across the last 550 million years, and you shifted to talking only about the Cenozoic.
I've explained to you why the Holocene is the relevant time period. We don't have data across the entire Cenozoic to examine climate processes on a decadal or annual scale, and the processes being studied in IPCC reports are on that scale. Data from a millenial scale are simply not relevant to questions about the impacts of doubling carbon dioxide concentrations over a few decades.
Factors like distance to the sun, angle to the sun, ocean circulation, asteroid impacts, intense volcanism, solar intensity, tectonics, shifts in air circulation can all influence climate on millenial scales, as can changes in atmospheric composition. Looking only at carbon dioxide concentration and temperature at millenial scales is inappropriate. At a decadal or annual scale, many of those factors are close to constant, and the major forcing on climate is the doubling of concentration of carbon dioxide and concomitant increases in other greenhouse gases.
It's likely that there has never been an increase of CO2 on that scale in such a short time period. Certainly not within the time period in which we have accurate data on the annual or decadal concentrations of carbon dioxide.
Talking about climate when there was an equatorial connection between Atlantic and Pacific as if it were comparable to modern climate is comparing apples and oranges. The number of factors you have to control for is immense, and most of the factors driving climate on a scale of millenia or millions of years are not relevant to contemporary climate change.
OK... so the guy got demoted, all because of politics. Still really stinks. You wouldn't like it either but I guess it happens all the time right?
For the citation please go review the book I referenced it should be in the KU Library. It is covered is several sections and I do not have the book at hand. Sorry.
There have been a couple of significant C02 spiking events caused by volcanoes, the Toba eruption 75,000 years ago and the Yellowstone eruption 650,000 years ago. The Toba event put up 22 megatonnes a day for several months. The Yellowstone event is estimated to have put up to 220 megatonnes CO2 into the air a day for several years. Compare that to the 22 megatonnes estimate yearly CO2 output attributed to human activity. That's the equivalent of a few 1000 years worth of humans burning it up.
He wasn't even demoted. The state eliminated the title in 1989, and he has not stopped using it. The governor is simply acting on the legislature's 18 year-old decision. His salary will be touched.
When you say "Tectonics and Milankovitch together cannot account for the amount of cooling together with the high levels of carbon dioxide," it sounds like you have seen a specific analysis of that question, not just handwaving. There are 18 papers in the book you referenced. Which were you thinking of?
Volcanoes put out CO2, but I was more interested in the ability of airborne particulate to lower global temperatures. They would also change light levels, killing plants on a global scale, which would also release a lot of CO2. Same for a large asteroid impact. Since there are not currently volcanoes producing anywhere near the level of CO2 you describe, and human activities are not blocking out the sun, your example only validates my point. Looking at decadal processes in recent history gives you more meaningful comparisons than cherry-picked examples from the last 500 million years.