what do we know and what do we not?

We know the surface temperature has warmed about 0.8°C over the past century. We know human GHG emissions are the main cause of this warming. We know that if we continue to emit large amounts of GHGs, the planet will continue to warm. We know this will cause some very bad impacts, like quickly rising sea levels as ice sheets collapse. We know that the planet will probably warm between 1.5 and 4.5°C in response to doubled atmospheric CO2.

What we don't know is exactly how much between 1.5 and 4.5°C the surface will warm. This is mainly because we don't know how clouds will respond to the warming temperatures, or how much of a cooling effect atmospheric aerosols have on global temps. Those are the big questions remaining to be answered. We also don't know exactly how regional climates will change in a warming world, because climate models don't have that kind of resolution.

So there are definitely significant questions we don't have the answers to. But we do have the answers to the big ones. We know we're causing dangerous global warming.

- We know beyond any doubt the earth is warming because we've measured it in many ways.

- We know that northern hemisphere spring has advanced about 2 weeks, and fall has fallen back maybe 1 week.

- We measure total CO2 atmospheric concentrations, and know they are rising, and by how much.

- We know that record high temperatures outnumber record low temperatures now by at least 2:1.

- We know more ice is melting than forming now, and that this has been going on for decades.

- We know that species are moving away from the tropics and up mountainsides.

- We know that weather has been getting more extreme, and there is more moisture in the air.

We know the general shape and scope of the problem of AGW. We do not know all the details. We've learned a lot, but have much more to learn. Others have mentioned the atmospherics, and where we are there. So I'll mention the oceans, and where we are not. We do not have a good appreciation of the methods of heat transfer between the deep ocean and the atmosphere, and this is one critical area. The ocean can soak up a lot of heat, and it can give it back. This heat exchange is most noted in the El Nino - La Nina events in the Pacific. We truly don't know what we are doing to the oceans, and what effect this will have on climate in the short, medium, and long-terms, but we do know that if we are pumping all this energy into the oceans, it has to come back out at some time. Just how, and what effects this energy will have, we will find out.

Another area I didn't see mentioned is biology/ecology. We apparently have turned the genii of rapid evolution loose, as the changing world climate pushes against all species ranges. This wave of changes has not yet begun to hit, and we don't know what will happen when it does, other than that it will cause problems. Monoculture food crops are not a good idea in this sort of situation. What is likely to happen is ecosystem collapse in various areas of the world, and invader species running rampant practically everywhere, after a while. And that's based on observations of what has happened in similar situations in the recent past - recent enough for us to study. The biosphere is expected to become relatively impoverished. We may find ourselves building anti-greenhouses to grow plants that require more cold than they can get naturally any more. Many plants require frosts to set, or other temperature signals, and so do animals. Look up the effect of water temperature on alligator eggs. The sex of the alligator is determined by the water temperature in at least some species. And this is not all that uncommon among species. What happens when 99% of the members of a species are the same sex?

We're playing a game with our civilization. We know we are screwing ourselves. We just don't know how badly.

What we don't know, is the difference between weather and climate, if the last two answers are anything to go by ...

Continuing in that mode; we don't know ...

that the LIA and MWP are irrelevant, as is the fact that dinosaurs didn't have SUV's,

the actual meaning of "No significant warming in the last 15 years",

the absurdity of "It's the Sun" as an explanation for the current warming!

I could go on all day ...

We can't point to specific hurricanes and say "This was caused by global climate change", same for floods or droughts. We do not know how much people will cut back on burning in the future, or how fast population will grow.

What we KNOW: The climate has cycles and varies according to the season, ocean currents and sun activity.

What we do not know: How to create an accurate 5 day forcast mush less a 100 year one.

enough said.

We have a very good understanding of the radiative forcing caused by the current CO2 concentration, and a rather poor understanding of the net radiative forcing (er, cooling?) caused by aerosols.

While this is not directly tied to AGW per se, we have a good understanding of the physics behind the existence of the tropospheric hot spot, and have observed it in short term data clearly, but we don't have good observational evidence of it in the long term.

The long term cloud feedback is a good one, that Bob brought up. I think there are good early indicators that the short term feedback is slightly positive, though the possibility of a negative feedback still exists as the uncertainty bounds extend below zero as well.

We are certain

-Based on fundamental physics and laboratory measurements of CO2 spectra that a doubling of CO2 will cause ~1 C of warming by itself (it's the fractional increase in CO2 which is important, no absolute increase). No one doubts this, not even "skeptics" like Lindzen, Monckton, or Singer.

We are not certain

-Exactly how clouds will respond in a warming world. There is even a remote chance they could provide a significant negative feedback, though a small climate sensitivity would have to be reconciled with past climate changes.

For over 50 years, scientists have known that increasing greenhouse gases warms average temperatures and changes global climate.

For over 30 years, scientists have known that greenhouse gases are in fact increasing and that this is due almost entirely to human causes.

For over 20 years, scientists have known that global average temperatures have been on an unusually rapid long term upwards trend, due at least mainly to the (above) man-made increase in greenhouse gases, and that such temperature increases are likely to eventually produce rapid (and slow to reverse) positive feedbacks.

True scientists were skeptical about all these points, until they were proven by massive research of independent and corroborating studies over decades by thousands of researchers in dozens of countries.

Phony "skeptics" were largely enabled by oil company funded deception campaigns of the 1990s. The con-artists and dupes of these deceptions today use a shifting mix of inconsistent lies and tricks to deny the real science. To their colossal historical shame, most of the current national-level Republican Party politicians in the U.S. have lined up solidly behind an associated steadfast campaign of incessant anti-science lies. Such amoral idiocy is recent. Even the George W. Bush administration was not so stupidly dishonest.

There is much that scientists still do not know about AGW or are quite unsure of, or are debating (how fast will future climate change come, how soon with strong feedbacks kick in, how severe will the consequences be, how well will human and natural systems be able to adapt, etc.). The copy-cap trainee liar-deniers on YA spend about 0.1% of their energy discussing such uncertainties, and 99.9% of their effort in replicating (often using below high school level science and English) these pre-fab oil company lies.

A renegade handful of the copy-cat liar-deniers on YA cheat massively. Based on hundreds of past instances, one or more of them is liable to use illegal aliases to "hide" answers such as this one by hitting them with 5+ thumbs downs or by falsely "reporting" them.

U.S. National Academy of Sciences, 2010:

http://books.nap.edu/openbook.php?record_id=12782&...

“Climate change is occurring, is caused largely by human activities, and poses significant risks for a broad range of human and natural systems.”

http://nationalacademies.org/morenews/20100716.htm...

“Choices made now about carbon dioxide emissions reductions will affect climate change impacts experienced not just over the next few decades but also in coming centuries and millennia…Because CO2 in the atmosphere is long lived, it can effectively lock the Earth and future generations into a range of impacts, some of which could become very severe.”

http://www.nasonline.org/site/PageServer?pagename=...

“The Academy membership is composed of approximately 2,100 members and 380 foreign associates, of whom nearly 200 have won Nobel Prizes. Members and foreign associates of the Academy are elected in recognition of their distinguished and continuing achievements in original research; election to the Academy is considered one of the highest honors that can be accorded a scientist or engineer.”

mother earth (aka Bloody Mama) farted. big words you have... i would bring mine out if i thought you were qualified to validate my existence, but i'm playing dumb natural healer. gore is a dork. your argument may be sound if we really had to blame weather trends on something/someone. i was hardcore hippie in the 60's and again in the 90's. i discovered it is all about the power and ego just like the churches. hippies are dumb, and that makes me dumb for joining them