State of the Union - Climate change?

[One Bad Pig]

Greenhouse gases are also produced by volcanic eruptions. In and of themselves, one or two large eruptions can change the climate.

Volcanic eruptions tend to have cooling effects rather than warming effects due to all the particulate that gets released. 1816 is known as "The year without a summer" for that reason.

[TheLurch]

The point is, we were much cooler during the ice age and have been trending warmer since (with your expected ups and downs of course). And way before that the earth was quite a bit warmer. So there is really no average temperature to compare to.

No, we HAVE NOT been trending warmer since. We trended warmer until the peak of the orbital forcings 7,000 years ago. Since then, we've been trending cooler. That cooling trend has been interrupted over the last century or so.

Put another way: we can't simply say "we're warmer than the depths of the last ice age, therefore we've been trending warmer." Trends are patterns in the data; a line connecting two points isn't a pattern.

[shunyadragon]

You really are an idiot Shuny. Are you really denying that the earth was cooler during the ice age? Or that way before that the earth was way warmer? And don't give me your layman crap when you do the same thing - hypocrite.


https://www.sciencenews.org/article/...-covered-trees

I simply referred to the academic sources, which you have failed to do to understand the science of climate change and paleoclimate cycles in history. Need academic sources and references from you, not personal opinions, name calling, and mindless accusations. Still waiting . . .

[seer]

The amount of CO2 in the atmosphere has risen since industrialization from abt. 280 ppm to 390 ppm (IPCC working group I report, page 166). We would expect temperature to rise because of that, and it does. In the debate you linked, both sides agree that the available data indicates a current rise in global temperature.

See, I have to find the reference, but from what I read we put only about 2% of the total in. And also from what I read Co2 was over 400 ppm in the distant past.

We have not been trending warmer since the last ice age. Deglaciation after the last ice age, the Weichsel stage, was very quick and was followed by shorter cold periods, the Older and Younger Dryas periods. Even after the Younger Dryas there has not been a singular warming trend; for example the "8.2 event" was another short cooling period. The smaller events are not seen globally.

I'm sorry Jonathan that just isn't correct. We were much cooler during the ice age until about 12,000 years ago. 5,000 years ago we were warmer than that, then we were cooler for a while, and then warmer, and warmer again in the last few centuries.

However, even if we were in a period of millennial-scale global warming, this would not matter to the greenhouse effect and current global warming, which is about the current warming trend that started in the 20th century and continues to this day. This has been researched thoroughly and natural forcings cannot explain it, while rising greenhouse gases in the atmosphere can. There are several trends on longer timescales - orbital forcings, climate change driven by plate tectonics, variations in solar radiation, etc., that take place on a longer timescale and influence our climate in the present as much as in the past. However, these mechanisms cannot explain the magnitude of warming that currently concerns our societies. That is not to say they are irrelevant or not happening, it's just a question of scale.

Well I'm not sure we understand all the possible variables.

[seer]

I simply referred to the academic sources, which you have failed to do to understand the science of climate change and paleoclimate cycles in history. Need academic sources and references from you, not personal opinions, name calling, and mindless accusations. Still waiting . . .

Yes Shuny, but as we have all seen over time - you seldom know what you are talking about and fancy yourself as an academic - which you are not.

[shunyadragon]

The first graph presented on the second page of the forbes article http://www.forbes.com/sites/petergle...limate-data/2/ showed an anomaly of above 0.4C in 1997 and below 0.55C in 2011. I doubt 2012 and 2013 were much above average, so I see a warming trend of near 0.15C since 1996 or 1997. That's close to flat in my eyes--the annual average is only near 0.01C. Besides, did any climate model include that outcome? Or even predict 0C or less? I think maybe less than 3 models. And if you will please reread my post, I only said that if this year and the next few years turn out to be cool enough, then all models known on this date will have failed to predict flatlining or cooling.

Climate models cannot predict year to year 'weather,' or weather in spans of three to five years. 'Chaos' rules on the short term variability of weather. A good foundation of Chaos math would help understand this, and how it plays out in nature over time. The patterns in weather and even long term 'climate' trends require many years of data to establish trends over time. The records in the Ice Cores of the Arctic and Antarctic are very useful in this, because they provide us with thousands of years of an accurate record of climate history, and other things like CO2 content in the atmosphere.

Someone questioned what I meant by "ocean oscillation cycle"--I meant something like Pacific decadal oscillation http://en.wikipedia.org/wiki/Pacific...al_oscillation

OK, but we need to relate this to long term climate trends. It does not stand alone.

[seer]

No, we HAVE NOT been trending warmer since. We trended warmer until the peak of the orbital forcings 7,000 years ago. Since then, we've been trending cooler. That cooling trend has been interrupted over the last century or so.

Good, at least you agree we were trending warmer for a while. Ok, so do we have average global temperatures that we can compare. From 5,000 years ago, 2,000 years ago, 1,000 years ago, 500 years ago? The whole point of this though is to see if there is any average global temperature - a normal.

[shunyadragon]

Good, at least you agree we were trending warmer for a while. Ok, so do we have average global temperatures that we can compare. From 5,000 years ago, 2,000 years ago, 1,000 years ago, 500 years ago? The whole point of this though is to see if there is any average global temperature - a normal.

We follow climate cycle trends. The average global temperature can be calculated and followed over periods of time and compared to CO2 contents of the atmosphere. The ice cores of the Arctic and Antarctic provide a good record to do this over period of over 800,000 years

[TheLurch]

Good, at least you agree we were trending warmer for a while. Ok, so do we have average global temperatures that we can compare. From 5,000 years ago, 2,000 years ago, 1,000 years ago, 500 years ago? The whole point of this though is to see if there is any average global temperature - a normal.

Before i go into detail on that, you mind if i ask how much you know about paleoclimate reconstructions? It'll help me determine the level of detail i provide in my answer.

[HMS_Beagle]

Good, at least you agree we were trending warmer for a while. Ok, so do we have average global temperatures that we can compare. From 5,000 years ago, 2,000 years ago, 1,000 years ago, 500 years ago? The whole point of this though is to see if there is any average global temperature - a normal.

Since quiz time!

Here is the correlation between historic CO2 level and historic global temperature as measured in Antarctic ice cores.

co2-vs-temp.jpg

For the last 300K years the CO2 level varied between 180 to 280 ppm. Then in the last 50 years it has shot up to almost 400 ppm. What effect do you think that will have on the average temperature?

[seer]

Before i go into detail on that, you mind if i ask how much you know about paleoclimate reconstructions? It'll help me determine the level of detail i provide in my answer.

I know what it paleo-climatology is, but no much more. The point is do we really even know what global temperatures were over these periods to any degree of certainty? I mean some things are obvious - there was an ice age, and mini-ice ages. Where I live in southern New England was once under a 50'+ glacier. The other reason I ask is because even with all our testing stations across the world today there seems to be discrepancies - differing interpretations. I was reading this guy - MIT Professor Richard Lindzen. If that is the case with all our modern technology how could we hope to get accurate readings from 500-1,000 years ago and such.

http://online.wsj.com/news/articles/...917025400.html

[seer]

Since quiz time!

Here is the correlation between historic CO2 level and historic global temperature as measured in Antarctic ice cores.

[ATTACH=CONFIG]177[/ATTACH]

For the last 300K years the CO2 level varied between 180 to 280 ppm. Then in the last 50 years it has shot up to almost 400 ppm. What effect do you think that will have on the average temperature?

I don't understand. In the last box of the graft the Co2 level shot up to like 380 PPM, but the temperature did not follow, it actually went down.

[TheLurch]

I know what it paleo-climatology is, but no much more. The point is do we really even know what global temperatures were over these periods to any degree of certainty? I mean some things are obvious - there was an ice age, and mini-ice ages. Where I live in southern New England was once under a 50'+ glacier. The other reason I ask is because even with all our testing stations across the world today there seems to be discrepancies - differing interpretations. I was reading this guy - MIT Professor Richard Lindzen. If that is the case with all our modern technology how could we hope to get accurate readings from 500-1,000 years ago and such.

http://online.wsj.com/news/articles/...917025400.html

Lindzen isn't very specific about what he considers the issues to be, so it's hard to address that. If you'd like to get into the accuracy of the modern instrument record, we can, but i prefer to deal with one thing at a time - at the moment, we're on paleoclimate.

So, how do you get a temperature from the past? The first is reliable dating. Some things, like tree rings, sediments, and ice cores are simple - there's a seasonal banded pattern, and if you can find something that gives you a specific date (like ash from a volcanic eruption), you can line up the whole thing on a timeline; carbon dating can also work well here when available. Then, you need to examine a given year's temperatures. There are multiple ways of doing this - oxygen isotopes, tree ring size, etc., each with their strengths and weaknesses. The wikipedia entry on climate proxies is quite good on this:
http://en.wikipedia.org/wiki/Proxy_(climate)

So, from those, you can get a rough idea of the past climate in one location in a given year, although it has substantial systemic errors (meaning something like +/-.1C). By taking multiple samples from the same region, you can start limiting the variation and cutting down on the errors.

That gives you a regional temperature. You then have to create a collection of different regional temperatures to start averaging into a global temperature. This involves things like taking geography into account - if you have a lot of samples from Europe and few from Australia, you weigh the Australian ones more, etc. In the end, you can come up with a global reconstruction. These tend to show a lot of variations on the decadal-scale (i.e., if you want the temperature of the 1560s, you'll get different answers with different methods and data sets), but they largely agree on climate trends of a few decades and more.

For a good technical report, i recommend this:
http://www.nap.edu/openbook.php?record_id=11676

The National Academies of Science are highly respected, and did a thorough overall analysis. It's now almost a decade old, so there have been a lot more studies published since, but reading it will give you a much stronger sense of how the scientific community has reached the conclusions it has.

Any questions about any of that? To be clear, i'm not trying to turn you into an expert. What i am trying to do is give a sense of how the science is done, and how the scientists doing it try to work within the limitations they face in order to produce reliable results.

[Jonathandavid]

I don't understand. In the last box of the graft the Co2 level shot up to like 380 PPM, but the temperature did not follow, it actually went down.

It's not global temperature in the graph.

(Man, that took me, 5 seconds? 6?)

Edit: HMS Beagle's question remains, Seer. "What effect do you think that [high level of CO2] will have on the average temperature?"

[One Bad Pig]

Since quiz time!

Here is the correlation between historic CO2 level and historic global temperature as measured in Antarctic ice cores.

[ATTACH=CONFIG]177[/ATTACH]

For the last 300K years the CO2 level varied between 180 to 280 ppm. Then in the last 50 years it has shot up to almost 400 ppm. What effect do you think that will have on the average temperature?

Temperature hasn't been tracking for the last 8,000 years or so. The data, it might not show what you think it does.