If You Want To Know The Science, Read This Post
While this thread isn't bad, it's plagued by the same problems as
every other thread related to science on SWF: a severe lack of understanding of the issues and the science behind them. A lot of people do not have the proper foundation in science or researching and interpreting credible sources/articles to be debating issues like this.
That said, this thread has done okay so far; adumbrodeus has done a good job of disseminating some facts. I'm going to hit you with more facts and hard science.
I'VE QUOTED A NUMBER OF SOURCES; QUOTES ARE
BLUE AND ITALICIZED
It's well established that global warming is real. The issue is whether or not humans play a big role in it.
The
National Climatic Data Center (NCDC), part of the
NOAA (National Oceanic and Atmospheric Administration) has a good FAQ on the whole issue:
http://www.ncdc.noaa.gov/oa/climate/globalwarming.html
The NCDC/NOAA acknowledge that there have been rapid climatic changes in the past (by studying paleoclimatic changes) during glacial (ice age) and interglacial transitions, but also that
"the projected change of 3 to 7°F (1.5 - 4°C) over the next century would be unprecedented in comparison with the best available records from the last several thousand years."
The NCDC also reported on global surface temperature anomalies (air temperature of a region at the time of measurement vs the long-term-mean air temperature of that region), and these data also show an unprecedented increase in global temperatures coinciding with the advent of industrialism and increased human emissions:
http://www.ncdc.noaa.gov/oa/climate/research/anomalies/anomalies.html
The data used to construct the graph come from a number of sources including the
Global Historical Climatology Network (GHCN), various climatologists, and the UK's
University of East Anglia's Climate Research Unit (UEA-CRU) among others.
Another leading center on climatology and paleoclimatology, the Argentine
Regional Center of Scientific and Technological Investigations (CRICYT) has this to say:
" Paleoclimatology offers to help answer each of these questions. Several of the paleoclimate studies reported on in this web document (Briffa et al., Mann et al., Overpeck et al.) have begun efforts to attribute past climate change to both natural and human causes, and to use this information to estimate how much of the current warming is due to humans (i.e., greenhouse warming). The best estimate is that about 50% of the observed global warming is now due to greenhouse gas increases."
(
http://wdc.cricyt.edu.ar/paleo/globalwarming/end.html)
(
http://wdc.cricyt.edu.ar/paleo/globalwarming/paleolast.html)
In other words,
50% of modern warming is estimated to be the result of
human activity; that is a huge number.
The same source (CRICYT) also says this regarding today's warming compared to earth's temperature from thousands of years ago:
" The latest peer-reviewed paleoclimatic studies appear to confirm that the global warmth of the 20th century may not necessarily be the warmest time in Earth's history, what is unique is that the warmth is global and cannot be explained by natural forcing mechanisms."
(
http://wdc.cricyt.edu.ar/paleo/globalwarming/paleobefore.html)
Here is what NASA has to say:
"In 2001, the Intergovernmental Panel on Climate Change (IPCC), a group sponsored by the United Nations (UN), published results of climate simulations in a report on global warming. Climatologists used three simulations to determine whether natural variations in climate produced the warming of the past 100 years. The first simulation took into account both natural processes and human activities that affect the climate. The second simulation took into account only the natural processes, and the third only the human activities.
The climatologists then compared the temperatures predicted by the three simulations with the actual temperatures recorded by thermometers. Only the first simulation, which took into account both natural processes and human activities, produced results that corresponded closely to the recorded temperatures. "
(
http://www.nasa.gov/worldbook/global_warming_worldbook.html)
This means that human activities are indeed influencing earth's current climate change in a very measurable, significant way; they are by no means negligible.
NASA's Earth Observatory also provides the following in a global warming FAQ:
"Q: If Earth has warmed and cooled throughout history, what makes scientists think that humans are causing global warming now?
A: The main reason that scientists think humans caused warming since 1950 is that none of the natural processes that influence Earth’s climate have changed enough during that time period to explain the warming."
Some claim that the sun's activity has played a role in the recent warming. This seems plausible at first, because changes in sun activity are in deed one of the major causes of earth's major ice ages. However, changes in sun activity cannot be used to explain today's warming. Here is how the NASA Earth Observatory answers:
"Even more telling is the way in which temperatures are rising. If the warming were caused by a more active Sun, then scientists would expect to see warmer temperatures in all layers of the atmosphere. Instead they have observed a warming at the surface and in the lower parts of the atmosphere and a cooling in the upper atmosphere. Something is trapping heat in the lower atmosphere, and that something is greenhouse gases."
(
http://earthobservatory.nasa.gov/Features/GlobalWarmingQandA/)
This is a very useful FAQ that answers many questions that skeptics have; please read it. Another good read on climate change and ice ages (though not necessarily from a global warming standpoint) is this site/lecture from a University of Arizona page:
http://ircamera.as.arizona.edu/NatSci102/NatSci102/lectures/climate.htm
The
NASA Goddard Institute for Space Studies (GISS) also agrees on the sun issue as well:
"...the solar increases do not have the ability to cause large global temperature increases...greenhouse gases are indeed playing the dominant role..."
(
http://www.giss.nasa.gov/research/news/19990408/)
The Stanford Solar Center adds:
"The Sun is once again less bright as we approach solar minimum, yet global warming continues."
(
http://solar-center.stanford.edu/sun-on-earth/glob-warm.html)
Abrupt climate change has occurred in the past. Isn't it possible that's what is occurring now?
The
Woods Hole Oceanographic Institute (WHOI), which has a section dedicated to abrupt climate change (shifts in climate that occur over a period of decades or centuries), acknowledges the following:
"Q. Have humans contributed to the warming?
A. Yes, but there is debate over how much. Natural variability - such as that arising from changes in the sun's energy input to Earth, volcanic activity, and regional climate phenomena like El Niño-Southern Oscillation (ENSO) - does play a role in adjusting the global thermometer. But the observed temperature record cannot be wholly accounted for by natural causes. As the American Geophysical Union recently concluded: "It is scientifically inconceivable that - after changing forest into cities, putting dust and soot into the atmosphere, putting millions of acres of desert into irrigated agriculture, and putting greenhouse gases into the atmosphere - humans have not altered the natural course of the climate system." Greenhouse gases such as carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), ozone (O3) and chlorofluorocarbons (CFC) are being added to the atmosphere largely as a result of burning fossil fuels, tropical deforestation and other human activities. These gases trap energy that would normally be radiated into space, and raise Earth's surface temperatures."
(
http://www.whoi.edu/page.do?pid=12455&tid=282&cid=10149#ocean_1)
They also show this graphic from a report by the
IPCC (Intergovernmental Panel on Climate Change):
Note the sharp increase just as the 20th century rolls around; that is the kind of temperature change that scientists say cannot be explained solely by natural factors.
In their report, the IPCC concluded that humans are causing modern global warming (
see this press report).
You can read the IPCC's full report at the following link (it is in PDF format); the document contains graphs and numbers for those interested:
http://www.ipcc.ch/pdf/assessment-report/ar4/wg1/ar4-wg1-spm.pdf
Additionally, the
US Climate Change Science Program says that human activity can cause abrupt climate change, like the warming we see now. You can read the full report here:
http://www.climatescience.gov/Library/sap/sap3-4/final-report/default.htm
The American Geophysical Union has this to say:
"The 1992 United Nations Framework Convention on Climate Change states as an objective the "...stabilization of greenhouse gas concentrations in the atmosphere at a level that would prevent dangerous anthropogenic interference with the climate system." AGU believes that no single threshold level of greenhouse gas concentrations in the atmosphere exists at which the beginning of dangerous anthropogenic interference with the climate system can be defined. Some impacts have already occurred, and for increasing concentrations there will be increasing impacts. The unprecedented increases in greenhouse gas concentrations, together with other human influences on climate over the past century and those anticipated for the future, constitute a real basis for concern.
...
The global climate is changing and human activities are contributing to that change."
(
http://www.agu.org/sci_soc/policy/positions/climate_change.shtml)
The American Meteorological Society agrees; you should read their full statement on it, but here is a brief excerpt regarding CO2:
"Carbon dioxide concentration is rising mostly as a result of fossil-fuel burning and partly from clearing of vegetation; about 50% of the enhanced emissions remain in the atmosphere, while the rest of the Earth system continues to absorb the remaining 50%. In the last 50 years atmospheric CO2 concentration has been increasing at a rate much faster than any rates observed in the geological record of the past several thousand years."
(
http://ametsoc.org/POLICY/2007climatechange.html)
Another IPCC report also details the solid evidence that
humans are responsible for increased CO2 and greenhouse gas levels:
http://www.ipcc.ch/pdf/climate-changes-2001/synthesis-spm/synthesis-spm-en.pdf
All the numbers, data, tables, and graphs within are quite a bit of proof.
Don't volcanoes and other natural sources emit thousands of times more CO2 than human activities?
The answer is a resounding "NO".
The
USGS Volcano Hazards Program says that
"Human activities release more than 130 times the amount of CO2 emitted by volcanoes--the equivalent of more than 8,000 additional volcanoes like Kilauea (Kilauea emits about 3.3 million tonnes/year)! (Gerlach et. al., 2002)"
(
http://volcanoes.usgs.gov/hazards/gas/index.php)
The Environmental Protection Agency (EPA) echoes and cites this:
"human activities now emit 130 times as much CO2 as volcanoes (whose emissions are relatively modest compared to some earlier times)."
(
http://www.epa.gov/climatechange/science/pastcc.html)
The EPA also cites studies that show dramatic increases in all greenhouse gases and concludes that they are the result of human industrial advancement.
http://www.epa.gov/climatechange/science/recentac.html
Need more proof that the increase in CO2 and greenhouse gases is the result of human activity?
The University Corporation for Atmospheric Research delivers:
"One of the strongest pieces of evidence for human-induced climate change is the consistent rise in carbon dioxide (CO2) in modern times"
(
http://www.ucar.edu/news/features/climatechange/faqs.jsp#globalwarming)
Data for that graph came from the Mauna Loa Observatory in Hawaii.
http://www.mlo.noaa.gov/
UCAR also answers those who say
Weren't scientists warning of a global cooling a few years ago?:
"After rising in the early 20th century, global surface temperatures cooled slightly from just after World War II (the mid-1940s) into the 1970s.
Scientists already knew that carbon dioxide was accumulating in the atmosphere and that it could lead to eventual global warming. In 1975, Wallace Broecker (Lamont-Doherty Earth Observatory) published the first major study with "global warming" in the title.
But a few researchers believed that pollution from burgeoning postwar industry was shielding sunlight and shading the planet, causing the observed cooldown. Some even theorized that a "snow blitz" could accelerate the cooling and bring on the next ice age. Their statements got major play in the media.
Starting in the 1970s, new clean-air laws began to reduce sulfates and other sunlight-blocking pollutants from U.S. and European sources, while greenhouse gases continued to accumulate unchecked. Global temperatures began to warm sharply in the 1980s and have continued rising since then.
Increasingly detailed models suggest that the more recent warmup can be attributed to greenhouse gases overpowering the effect of sunlight-shielding pollution. Computer simulations also suggest that today's atmosphere would be even warmer still, were it not for that air pollution."
(
http://www.ucar.edu/news/features/climatechange/faqs.jsp#globalcooling)
UCAR also answers the following:
It's been freezing cold with lots of snow where I live. Doesn't that prove global warming is a hoax?
"There are always cold spells and warm spells going on in one place or another. But even where weather is cold, what's considered "typical" is changing. For example, the heavy snow that struck Colorado and Kansas at the end of 2006 was actually more characteristic of that area's autumn or spring weather than a typical December.
Globally, Earth's natural processes don't follow a linear pattern, so the global average temperature may be slightly cooler or warmer from one year to the next. Different parts of Earth's ecosystem also respond to the greenhouse effect in different ways. The oceans, for example, hold more heat and respond to atmospheric chnages more slowly than land masses do. Average temperatures of the land, oceans, and atmosphere also vary from year to year as well as from each other.
To examine long-term warming, climate scientists look at large areas and longer time periods. The maps below help illustrate the global nature of climate change."
(
http://www.ucar.edu/news/features/climatechange/faqs.jsp#cold)
If those reports weren't enough, here's another gigantic report from the
US Global Change Research Program. that also agrees humans have strongly impacted the climate:
http://www.usgcrp.gov/usgcrp/Library/ocp2008/ocp2008.pdf
http://www.usgcrp.gov/usgcrp/Library/ocp2008/default.htm
And here's another report from the IPCC on how strongly humans have impacted the climate:
http://www.ipcc.ch/pdf/technical-papers/climate-change-water-en.pdf
Whew, finally. Done.
