Other Answers (11)

• It%26#039;s legitimate. The progression in scientific understanding is summarized on this site:
  http://www.aip.org/history/climate/co2.h...
  
  Take for example the fact that an increase in CO2 has often lagged temperature rise in past warmings. Deniers claim, ignorantly, that this proves CO2 cannot cause warming, when that%26#039;s far from true:
  
  http://www.aip.org/history/climate/cycle...
  %26quot;An important clue came from some especially good ice core records that showed a lag in the levels of CO2 and methane. They seemed to rise or fall a few centuries after a rise or fall in temperature. This confused many people, who thought the time lag contradicted the greenhouse theory of global warming. But in fact the lag was not good news. Scientists quickly realized that it strongly confirmed that the Milankovitch-cycle shifts in sunlight initiated a powerful feedback loop. Evidently the close of a glacial era came when a slight rise of temperature stimulated massive changes in gas levels, which drove the temperature still higher, which drove further changes in the gas levels, and so forth. Ice ages were thus the reverse of our current situation, where humanity was initiating the change by adding greenhouse gases. Once that began to warm the planet, would the feedbacks begin to drive things higher on their own?%26quot;
  
  %26quot;It was now clear that not only the most obvious feedback, but also the most momentous one, was the connection between global temperature and greenhouse gas levels. Relatively straightforward analysis of the data showed that a doubled level of CO2 had always gone along with a rise of a few degrees in global temperature. It was a striking verification, with entirely independent methods and data, of what computer models had been predicting for the planet’s greenhouse future.%26quot; 0% 0 Votes
  
  We know it%26#039;s warming, and we%26#039;ve measured how much:
  
  http://www.epa.gov/climatechange/science...
  
  Scientists have a good idea how the Sun and the Earth%26#039;s natural cycles and volcanoes and all those natural effects change the global climate, so they%26#039;ve gone back and checked to see if they could be responsible for the current global warming. What they found is:
  
  Over the past 30 years, all solar effects on the global climate have been in the direction of (slight) cooling, not warming. This is during a very rapid period of global warming.
  
  http://news.bbc.co.uk/2/hi/uk_news/62902...
  http://www.pubs.royalsoc.ac.uk/media/pro...
  
  So the Sun certainly isn%26#039;t a large factor in the current warming. They%26#039;ve also looked at natural cycles, and found that we should be in the middle of a cooling period right now.
  
  %26quot;An often-cited 1980 study by Imbrie and Imbrie determined that %26#039;Ignoring anthropogenic and other possible sources of variation acting at frequencies higher than one cycle per 19,000 years, this model predicts that the long-term cooling trend which began some 6,000 years ago will continue for the next 23,000 years.%26#039;%26quot;
  
  http://en.wikipedia.org/wiki/Milankovitc...
  http://www.sciencemag.org/cgi/content/ab...
  
  So it%26#039;s definitely not the Earth%26#039;s natural cycles. They looked at volcanoes, and found that
  
  a) volcanoes cause more global cooling than warming, because the particles they emit block sunlight
  
  b) humans emit over 150 times more CO2 than volcanoes annually
  
  http://volcano.und.edu/vwdocs/Gases/man....
  
  So it%26#039;s certainly not due to volcanoes. Then they looked at human greenhouse gas emissions. We know how much atmospheric CO2 concentrations have increased over the past 50 years:
  
  http://en.wikipedia.org/wiki/Image:Mauna...
  
  And we know from isotope ratios that this increase is due entirely to human emissions from burning fossil fuels. We know how much of a greenhouse effect these gases like carbon dioxide have, and the increase we%26#039;ve seen is enough to have caused almost all of the warming we%26#039;ve seen over the past 30 years (about 80-90%). You can see a model of the various factors over the past century here:
  
  http://en.wikipedia.org/wiki/Image:Clima...
  
  This is enough evidence to convince almost all climate scientists that humans are the primary cause of the current global warming. 8% 8 Votes
  http://ipcc-wg1.ucar.edu/wg1/wg1-report....
  summarized at:
  http://www.ipcc.ch/pdf/assessment-report...
  
  There%26#039;s a lot less controversy about this is the real world than there is on Yahoo answers:
  
  http://www.worldpublicopinion.org/pipa/a...
  
  And vastly less controversy in the scientific community than you might guess from the few skeptics talked about here:
  
  http://en.wikipedia.org/wiki/Scientific_...
  http://www.sciencemag.org/cgi/content/fu...
  
  %26quot;There%26#039;s a better scientific consensus on this [climate change] than on any issue I know... Global warming is almost a no-brainer at this point. You really can%26#039;t find intelligent, quantitative arguments to make it go away.%26quot;
  
  Dr. Jerry Mahlman, NOAA
  
  Good websites for more info:
  
  http://www.nrdc.org/globalWarming/f101.a...
  http://www.ucsusa.org/global_warming/sci...
  http://www.realclimate.org
  %26quot;climate science from climate scientists%26quot;
  http://environment.newscientist.com/chan... 3% 3 Votes
• It appears that the earth%26#039;s temperature is increasing; glaciers have been retreating for years. However, changes in the earth%26#039;s temperature are nothing new; remember the Ice Ages? (Actually, you aren%26#039;t old enough.) It also is known that the atmospheric concentration of CO2 is increasing; this, too, is nothing new, as it was four times as high during the dinosaur era as it is now. Are these effects related? Possibly, but the evidence is that temperature changes occurred first, so that increased CO2 is a result, not a cause, of global warming. Various articles in Nature magazine. 7% 7 Votes
• It is not manufactured. At least the science is not. The public reaction to it is most definitely manufactured. 11% 12 Votes
• Well legitimate is my answer. They found 600 000m2 of rubbish in the ocean between ca and hawaii. Now if it was planned by politicians, how would have they done it ?!
  It can only be the mistakes of millions of people thinking that rubbish just disappears into thin air!
  But it is definitly an issue and it%26#039;s about time every politician listens to what greens have tried to scream for too many years!