Depends on whom you ask. Depends on your definition of "man-made". Also, the scientific community does not have any consensus on GW, at this point. Any concensus you may have read about or hear about - are generally politically driven - since this is a "hot" button for many.
Pretty sad actually - Politics driving real science out and forcing many good scientists take a stand on one side of the fence or other, all the while dangling a carrot (funding for research) if you help focus the research and publish results that will help tow my Political line and message.
But I digress - To help take some of the confusion out of this - lets make sure that everyone is on the same page here. Let's start with the popular definition of "global warming"? Some definitions are as follows:
- A gradual warming of the Earth's atmosphere reportedly caused by the burning of fossil fuels and industrial pollutants.
- The progressive gradual rise of the earth's surface temperature thought to be caused by the greenhouse effect and responsible for changes in global climate patterns. An increase in the near surface temperature of the Earth.
- An overall increase in world temperatures which may be caused by additional heat being trapped by greenhouse gases.
- An increase over time of the average temperature of Earth's atmosphere and oceans.
- The slow increase of the Earth's surface temperature.
- The gradual warming of the earth due to the "greenhouse effect".
- An increase in the temperature of the Earth's surface caused by trapping infrared radiation in carbon dioxide, increased amounts of which are produced by burning fossil fuels.
As you can see - most of the definitions for Global Warming center around these "greenhouse gases" - largely CO2 (produced by both man-made and natural sources) that influence the climate, trending to an increased planet temperature.
My definition of GW - "Global contrasts in the climate taking into account all enhancements of the greenhouse compared with natural variations."
Can't really say if GW is man made event or not - it is very easy to point the finger at the human enhancements to the gobal scene - the Kyoto accord in the late 90's doesn't help matters either. But I will say that mankind does have some influence on the climate - but at much smaller scales than what the popular prevailing idea suggests.
To say that GW was solely based on pollution generated by transportation and power generation is totally bogus. Actually, looking at the global scale - these only contribute a fraction of the total worldwide generation of these emissions. The biggest gas emission of interest is methane.
Over the last two centuries or so, methane concentrations in the atmosphere globally - have more than doubled. The rate of growth has started to taper off a bit - but the amount of methane present is still quite a bit higher than previous records indicated (also compared to 400,000 year old air pockets trapped in ice). Methane has a life span of 10-15 years in the atmosphere and is 20x more effective than CO2 in its ability to "warm" the planet. Largest man-made sources of methane are landfills and agriculture. Methane is also one of the most common natural emission as well. But you have to ask - so what. This looks really bad for man - since we are solely responsible for our part of generating all these excess gasses.
But even if you pumped 10x more methane into the atmosphere and CO2 to match - it would be an insignificant fraction compared (about 5% if you take into account the #1 natural source, about 0.3% if you don't) to the number 1 leading greenhouse gas - WATER VAPOR. Almost all of the water vapor produced is natural. Sure, locally, pollution from transportation and power generation make the air around you pretty dirty - but on a global sense - doesn't even put a dent into the overall picture.
Couple all these gasses with external events (recent research (2000+) have pointed to cosmic sources (more sensitive scientific packages, starting to look at the "BIG" picture) - the cyclical eccentricities in Earth's rotation and orbit, variations in the sun's energy output, and the cyclical waves of cosmic radiation - potentially accounting for atleast 75% influence of our climate. Pretty scary - we do not have as much control over the climate as we thought we did.
Given this - GW is NOT solely man-made. We do have some influence - but only to about 0.3% of the picture (greenhouse gas emission-wise).
Does that mean that we should not care about what man can do - not at all, man has a responsibility to himself to himself and to the environment - to whatever faction we can do, we should. Greenhouse emissions from transportation and power generation is a small part that w can control - we can also control emissions from landfills, agriculture, deforestation, and recovery of natural resources. Fossil fuels are a finite resource - it will eventually run out - it may be tomorrow, it may be thousands of years - but it will eventually run out. Mankind has the ability to adapt to innovate - we have to be accountable for our actions. If you cut down a forest - replant it. If you make a mess - clean it up. Common sense kind of stuff. This will all make great changes for the local scale (cleaner air for example) - on a global scale it really doesn't matter too much, as external events have so much more influence than what we can every do.
All this info can be found in these reference:
- IEA Greenhouse Gas R&D Programme, Gloucestershire, United Kingdom
- Carbon Dioxide Information Analysis Center (DoE) Oak Ridge, Tennessee
- U.S. Environmental Protection Agency
- William C. Trogler, Eric Bruner, Glenn Westwood, Barbara Sawrey, and Patrick Neill, Department of Chemistry and Biochemistry, University of California at San Diego, La Jolla, California
- SM. Freidenreich and V. Ramaswamy, “Solar Radiation Absorption by Carbon Dioxide, Overlap with Water, and a Parameterization for General
Circulation Models,” Journal of Geophysical Research 98 (1993)
- Patrick J. Michaels, DR., "Global Deception: The Exaggeration of the Global Warming Threat", 1998, Virginia State Climatologist and Professor of Environmental Sciences, University of Virginia
- Tim Patterson, DR., "The Geologic Record and Climate Change", 2005, Professor of Geology, Carleton University, Ottawa, Canada
- Nir Shaviv, DR., Racah Institute of Physics, Hebrew University of Jerusalem (astrophysicist)
- Jan Veizer, Dr., University of Ottawa in Canada (geochemist)
