dixieflatline
11-08-2004, 12:55 PM
This has been brought up in another thread but I wanted to start a seperate thread to discuss this. Lot's of interesting viewpoints were brought up and the science that in the field is moving forward very rapidly so it can be hard to keep up with.
There are really two parts to the question. First, is the earth really heating up? And then if it is are human's to blame?
Let's start with the first question. There isn't any science behind this it's just a simple measurement. Here is a link to several graphs looking at the mean temperature of the planet:
hxxp://www.pbs.org/wgbh/warming/etc/graphs.html
This is from a NOVA-frontline production on PBS that aired april 2000. The first graph shows the mean temperature of the earth from records of measurements from thermometers. This record goes back to about 1850 and seems to show a recent increase. This is a very short period of time but scientists can also measure the earth's temperature indirectly by looking at trees and ice layers etc... Combining all of these indirect measurements the second graph shows the earth's temperature for the last 1000 years. On this graph it's pretty clear that the temperature is rising in the last 100 years. If you are interested in these indirect measures of the temperature more can be found on this at the PBS website.
So the earth is heating up. This doesn't mean that human's are the cause of the increase. The earth naturally goes though cycles of much wider temperature swings that we see on these graphs. One poster mentioned volcanos which play a huge role in the earth's climate. Natural causes like that or el nino's etc... certainly play an important role. How can we be sure that we are causing the increase?
In fact if you read the transcript or watch the show you will get lot's of guesses but no conclusion as to the scource of the temperature increase. The thoery that greenhouse gasses such as CO2 are to blame is presented and the next two graphs on the link show the ammount of CO2 in the air for the last 40 years(directly measured) and the last 400,000 years(indriectly measured again using the ice cores). Again it's pretty clear that the ammount of CO2 in the air has reached a significantly higher ammount in the most recent years. This doesn't prove that the CO2 was to blame though.
This program though was aired in early 2000 and today it's generally accepted in the science community that indeed global warming is caused by greenhouse gasses such as CO2. There now is a lot of evidence to support this claim but I'm am not an expert in the field so I am only going to show one compelling reason for why scientists now believe greenhouse gasses are to blame.
hxxp://www.esr.org/outreach/climate_change/mans_impact/man1.html
talks a lot about what I just said and at the bottom of the page they show several graphs that are computer simulations of the earth's climate and the real temperature over the last 150 years. The upper left plot shows these models only simulating effects from natural causes(volcanos etc...). This simulation does a reasonable but not great job up to about 1970 and then fails miserably. The upper right plot shows this simulations only using anthropogenic, or human, activity. This graph does a good job predicting the upswing in temperature around 1970 but was way off before that. The bottom plot shows the simulations using both the human and natural effects and now the simulations are spot on. They correctly predict an increase around 1920 that levels off and then another increase around 1970.
A huge technical report can be found at hxxp://www.grida.no/climate/ipcc_tar/vol4/english/index.htm
with more discussion about the computer models and other evidence. This was also talked about in a recent edition of Scientific American Frontiers. You can watch this part of the show here:
hxxp://www.pbs.org/saf/1404/video/watchonline.htm
It's the second second link titled "the heat is on". For some reason before they talk about trusting these computer simulations they show what these simulations predict for the polar ice caps so you can fastfoward through that part if you like.
Note that I haven't said anything about what the U.S. or other contries should do about this. This is a much messier question and I am not about to say that everyone should stop using fossil fuels but I think it's fair to say that the science does point to these CO2 emissions as the cause of global warming.
There are really two parts to the question. First, is the earth really heating up? And then if it is are human's to blame?
Let's start with the first question. There isn't any science behind this it's just a simple measurement. Here is a link to several graphs looking at the mean temperature of the planet:
hxxp://www.pbs.org/wgbh/warming/etc/graphs.html
This is from a NOVA-frontline production on PBS that aired april 2000. The first graph shows the mean temperature of the earth from records of measurements from thermometers. This record goes back to about 1850 and seems to show a recent increase. This is a very short period of time but scientists can also measure the earth's temperature indirectly by looking at trees and ice layers etc... Combining all of these indirect measurements the second graph shows the earth's temperature for the last 1000 years. On this graph it's pretty clear that the temperature is rising in the last 100 years. If you are interested in these indirect measures of the temperature more can be found on this at the PBS website.
So the earth is heating up. This doesn't mean that human's are the cause of the increase. The earth naturally goes though cycles of much wider temperature swings that we see on these graphs. One poster mentioned volcanos which play a huge role in the earth's climate. Natural causes like that or el nino's etc... certainly play an important role. How can we be sure that we are causing the increase?
In fact if you read the transcript or watch the show you will get lot's of guesses but no conclusion as to the scource of the temperature increase. The thoery that greenhouse gasses such as CO2 are to blame is presented and the next two graphs on the link show the ammount of CO2 in the air for the last 40 years(directly measured) and the last 400,000 years(indriectly measured again using the ice cores). Again it's pretty clear that the ammount of CO2 in the air has reached a significantly higher ammount in the most recent years. This doesn't prove that the CO2 was to blame though.
This program though was aired in early 2000 and today it's generally accepted in the science community that indeed global warming is caused by greenhouse gasses such as CO2. There now is a lot of evidence to support this claim but I'm am not an expert in the field so I am only going to show one compelling reason for why scientists now believe greenhouse gasses are to blame.
hxxp://www.esr.org/outreach/climate_change/mans_impact/man1.html
talks a lot about what I just said and at the bottom of the page they show several graphs that are computer simulations of the earth's climate and the real temperature over the last 150 years. The upper left plot shows these models only simulating effects from natural causes(volcanos etc...). This simulation does a reasonable but not great job up to about 1970 and then fails miserably. The upper right plot shows this simulations only using anthropogenic, or human, activity. This graph does a good job predicting the upswing in temperature around 1970 but was way off before that. The bottom plot shows the simulations using both the human and natural effects and now the simulations are spot on. They correctly predict an increase around 1920 that levels off and then another increase around 1970.
A huge technical report can be found at hxxp://www.grida.no/climate/ipcc_tar/vol4/english/index.htm
with more discussion about the computer models and other evidence. This was also talked about in a recent edition of Scientific American Frontiers. You can watch this part of the show here:
hxxp://www.pbs.org/saf/1404/video/watchonline.htm
It's the second second link titled "the heat is on". For some reason before they talk about trusting these computer simulations they show what these simulations predict for the polar ice caps so you can fastfoward through that part if you like.
Note that I haven't said anything about what the U.S. or other contries should do about this. This is a much messier question and I am not about to say that everyone should stop using fossil fuels but I think it's fair to say that the science does point to these CO2 emissions as the cause of global warming.