You've forgotten the Fundamental Theorem of AGW.
A follows B, therefore, A caused B.How can climate scientists using in some cases only 30 years worth of data?
The fact that you're utterly ignorant of the evidence (even though it's been presented to you dozens of times) does not mean the evidence doesn't exist.
You are the posterchild of denial, andy.
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No other possible cause can be found. Changes in the sun happen over cycles of about 11 years and don't explain the degree of warming in the past year. The cycles that cause ice ages to come and go operate very slowly and would naturally be causing very slow cooling right now. The warming is not happening by magic, there is some physical reason. No natural cause fits the evidence. We have known that CO2 is a greenhouse gas since the 1800s. We know the CO2 in the air comes from burning fuels. Warming has been greatest in the northern hemisphere where the is the most CO2 because economies are more active. The warming correlates with increased CO2. Man made greenhouse gasses are the only possible cause that has not been eliminated. So unless some previously unconsidered natural cause is identified, AGW is the only explanation.
As MTR notes, they use a lot more than just 30 years of data, and a lot more than just correlation between CO2 and global temperature. You're grossly oversimplifying. If that's all they did, all we would need is one climate scientist with a calculator. Hell, I could do that.
The reason they can say for a fact that we know humans are driving global warming is because of the physics discussed in the link below.
http://greenhome.huddler.com/wiki/global鈥?/a>
As a side note, AGW deniers rarely use more than 8 years of data, and often just 1 day of data. So you should be asking yourselves this question.
You're right, it's very difficult to work on 30 years of data.
Scientists get together whatever they can. The longest continuous temperature record is HadCRUT3's surface station data, but that only goes back to 1850.
So we rely on geological records. Isotope and other records give us a huge amount of data - we have annual records going back 2,000yrs or so, decadal/centennial resolution temperature records going back 650,000 or so years from ice cores and lower precision ones going back millions of years.
Climate science isn't based on drawing simple correlations, but on underlying physics and advanced mathematical analysis. Climate models are tested against thousands of years of proxies and if you read a few papers all the way through you'll see that the uncertainties are well stated.
Baccheus makes the mistake of confusing the inability to prove another cause with the ability to rule out all other causes.
Moreover, what was a very rough correlation has really fallen off in the last 10 years.
It's cherry-picking a starting point for a graph. One of the most basic ways to lie with statistics.
http://www.amazon.com/How-Lie-Statistics鈥?/a>
Because if they look beyond the 1970's cooling period for ther reference point then their theory fall apart completely as they will ahve little to no data supporting them.
the ';30 years of data'; thing is a running mean value to reduce variability to study long-term trends. 30 years is used because it is relatively long in terms of human (a generation or so), and is sort of a statistical minimum number of observations needed to get meaningful results from normally distributed data. Climatologist may perform a 30 year running mean on thousands of years of data, or they may use a different averaging number (100 years or 5 years for example). Depends on the study. If they are looking at changes in the forest 50 or 100 year running mean values may be appropriate because of the life span of a forest. If they are just trying to reduce the variability enough to get a hint at an emerging long term trend, they may use a 5 year running mean.
If you are unfamiliar with these statistics, here is a quick explanation.
http://en.wikipedia.org/wiki/Moving_aver鈥?/a>
Also, they use way more than 30 years of data to model the impact of increasing CO2 on temps. They reconstruct information from ice cores, fossil records and tree rings for thousands of years. The also have physics and chemistry performed since the 1800s to define the relationship between CO2 and temperature. The relationship is causal because it is reproducible in the laboratory and the mechanisms that cause the relationship have been observed and quantified. Long wave radiation causes greenhouse gases to vibrate when they contact them. The thermal energy become kinetic energy. The green house gases them emit energy back into the air through this vibration.
To indicate they think AGW is occurring from 30 years of data is bogus and you know it.
Well, something's driving the observed climate change over the last 30 years, and
1. It's not orbital forcing, which causes ice ages, because orbital forcing peaked 6000 years ago and will be cooling the Earth for the next 23,000 years.
http://www.sciencemag.org/cgi/content/ab鈥?/a>
2. It's not the Sun. If the Sun is causing the current warmth, then we're getting more energy, and the whole atmosphere should be getting warmer. If it's greenhouse, then we're getting the same amount of energy, but it's being distributed differently: more heat is trapped at the surface, and less heat is escaping to the stratosphere. So if it's the Sun, the stratosphere should be warming, but if it's greenhouse, the stratosphere should be cooling.
In fact, the stratosphere has been on a long-term cooling trend ever since we've been keeping radiosonde balloon records in the 1950's. Here's the data:
http://hadobs.metoffice.com/hadat/images鈥?/a>
3. If it's the Sun, we're getting more energy during the day, and daytime temperatures should be rising fastest. But if it's greenhouse, we're losing less heat at night, and nighttime temperatures should be rising fastest.
In fact, minimum nighttime temps have risen about twice as fast as maximum daytime temps during the last 100 years. Here's the data:
http://www.ncdc.noaa.gov/gcag/GCAGdealte鈥?/a>
4. Total solar irradiance has been measured by satellite since 1978, and during that time it has shown the normal 11-year cycle, but no long-term trend. Here's the data:
http://www.ngdc.noaa.gov/stp/SOLAR/solar鈥?/a>
5. Scientists have looked closely at the solar hypothesis and have strongly refuted it. Here's the peer-reviewed science:
http://www.pubs.royalsoc.ac.uk/media/pro鈥?/a>
6. CO2 levels in the air were stable for 10,000 years prior to the industrial revolution, at about 280 parts per million by volume (ppmv). Since 1800, CO2 levels have risen 38%, to 385 ppmv, with no end in sight. Here's the data:
http://farm4.static.flickr.com/3006/2615鈥?/a>
So what's YOUR hypothesis?
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