The prevailing scientific opinion on climate change is that "most of the observed increase in globally averaged temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations," which leads to warming of the surface and lower atmosphere by increasing the greenhouse effect. Greenhouse gases are released by activities such as the burning of fossil fuels, land clearing, and agriculture. Other phenomena such as solar variation have had smaller but non-negligible effects on global temperature trends since 1950.http://en.wikipedia.org/wiki/Global_warming
"The world's leading climate scientists said global warming has begun, is very likely caused by man, and will be unstoppable for centuries, ... . The phrase very likely translates to a more than 90 percent certainty that global warming is caused by man's burning of fossil fuels. That was the strongest conclusion to date, making it nearly impossible to say natural forces are to blame."
"The report said that an increase in hurricane and tropical cyclone strength since 1970 more likely than not can be attributed to man-made global warming. The scientists said global warming's connection varies with storms in different parts of the world, but that the storms that strike the Americas are global warming-influenced."
"On sea levels, the report projects rises of 7-23 inches by the end of the century. That could be augmented by an additional 4-8 inches if recent surprising polar ice sheet melt continues."
 Joint science academies’ statement
In 2005 the national science academies of the G8 nations, plus Brazil, China and India, three of the largest emitters of greenhouse gases in the developing world, signed a statement on the global response to climate change. The statement stresses that the scientific understanding of climate change is now sufficiently clear to justify nations taking prompt action , and explicitly endorsed the IPCC consensus.
 US National Research Council, 2001
In 2001 the Committee on the Science of Climate Change of the National Research Council published Climate Change Science: An Analysis of Some Key Questions . This report explicitly endorses the IPCC view of attribution of recent climate change as representing the view of the science community:
The changes observed over the last several decades are likely mostly due to human activities, but we cannot rule out that some significant part of these changes is also a reflection of natural variability. Human-induced warming and associated sea level rises are expected to continue through the 21st century... The IPCC's conclusion that most of the observed warming of the last 50 years is likely to have been due to the increase in greenhouse gas concentrations accurately reflects the current thinking of the scientific community on this issue. 
 American Meteorological Society
The American Meteorological Society (AMS) statement adopted by their council in 2003 said:
There is now clear evidence that the mean annual temperature at the Earth's surface, averaged over the entire globe, has been increasing in the past 200 years. There is also clear evidence that the abundance of greenhouse gases in the atmosphere has increased over the same period. In the past decade, significant progress has been made toward a better understanding of the climate system and toward improved projections of long-term climate change... Human activities have become a major source of environmental change. Of great urgency are the climate consequences of the increasing atmospheric abundance of greenhouse gases... Because greenhouse gases continue to increase, we are, in effect, conducting a global climate experiment, neither planned nor controlled, the results of which may present unprecedented challenges to our wisdom and foresight as well as have significant impacts on our natural and societal systems. 
 Federal Climate Change Science Program, 2006
On May 2, 2006, the Federal Climate Change Science Program commissioned by the Bush administration in 2002 released the first of 21 assessments that concluded that there is clear evidence of human influences on the climate system (due to changes in greenhouse gases, aerosols, and stratospheric ozone) . The study said that observed patterns of change over the past 50 years cannot be explained by natural processes alone, though it did not state what percentage of climate change might be anthropogenic in nature.
 Other organizations
Other scientific organizations have made position statements on climate change.
* American Geophysical Union position statement on greenhouse gases and climate change (also endorsed by the American Institute of Physics)
* Climate Change Science: An Analysis of Some Key Questions, National Academy of Sciences, Commission on Geosciences, Environment and Resources, (Washington, DC: National Academy Press, 2001).
* Joint statement on the Science of Climate Change, issued by the Australian Academy of Sciences, Royal Flemish Academy of Belgium for Sciences and the Arts, Brazilian Academy of Sciences, Royal Society of Canada, Caribbean Academy of Sciences, Chinese Academy of Sciences, French Academy of Sciences, German Academy of Natural Scientists Leopoldina, Indian National Science Academy, Indonesian Academy of Sciences, Royal Irish Academy, Accademia Nazionale dei Lincei (Italy), Academy of Sciences Malaysia, Academy Council of the Royal Society of New Zealand, Royal Swedish Academy of Sciences, and Royal Society (UK).
* A position paper of the Stratigraphy Commission of the Geological Society of London.
* Position Statement on Global Climate Change adopted by the Geological Society of America
* Policy Statement on Climate Variability and Change by the American Association of State Climatologists (AASC)
* Australian Medical Association statement on climate change
* American Chemical Society statement on Global Climate Change
The only major scientific organization that rejects the finding of human influence on recent climate is the American Association of Petroleum Geologists.
 Recent Surveys of scientists
Various surveys have been conducted to determine a scientific consensus on global warming. Few have been conducted within the last ten years.
 Oreskes, 2004
In December 2004, an article by geologist and historian of science Naomi Oreskes summarized a study of the scientific literature on climate change. The essay concluded that there is a scientific consensus on the reality of anthropogenic climate change. The author analyzed 928 abstracts of papers from refereed scientific journals between 1993 and 2003, listed with the keywords "global climate change". The abstracts were divided into six categories: explicit endorsement of the consensus position, evaluation of impacts, mitigation proposals, methods, paleoclimate analysis, and rejection of the consensus position. 75% of the abstracts were placed in the first three categories, thus either explicitly or implicitly accepting the consensus view; 25% dealt with methods or paleoclimate, thus taking no position on current anthropogenic climate change; none of the abstracts disagreed with the consensus position, which the author found to be "remarkable". It was also pointed out, "authors evaluating impacts, developing methods, or studying paleoclimatic change might believe that current climate change is natural. However, none of these papers argued that point."http://en.wikipedia.org/wiki/Scientific_opinion_on_climate_change
30 years of solar variability.
30 years of solar variability.
Main article: Solar variation
Modelling studies reported in the IPCC Third Assessment Report (TAR) found that volcanic and solar forcings may account for half of the temperature variations prior to 1950, but the net effect of such natural forcings has been roughly neutral since then. The IPCC Fourth Assessment Report (AR4) gives a best estimate for radiative forcing from changes in solar activity of +0.12 watts per square metre. This is less than half of the estimate given in the TAR. For comparison the combined effects of all human activity are estimated to be an order of magnitude greater at +1.6 watts per square metre
Some researchers (e.g. Stott et al. 2003) believe that the effect of solar forcing is being underestimated and propose that solar forcing accounts for 16% or 36% of recent greenhouse warming. Others (e.g. Marsh and Svensmark 2000) have proposed that feedback from clouds or other processes enhance the direct effect of solar variation, which if true would also suggest that the effect of solar variability was being underestimated. In general, the IPCC describes the level of scientific understanding of the contribution of variations in solar irradiance to historical climate changes as "low."
The present level of solar activity is historically high. Solanki et al. (2004) suggest that solar activity for the last 60 to 70 years may be at its highest level in 8,000 years; Muscheler et al. disagree, suggesting that other comparably high levels of activity have occurred several times in the last few thousand years. Solanki concluded based on their analysis that there is a 92% probability that solar activity will decrease over the next 50 years. In addition, researchers at Duke University (2005) have found that 10–30% of the warming over the last two decades may be due to increased solar output. In a review of existing literature, Foukal et al. (2006) determined both that the variations in solar output were too small to have contributed appreciably to global warming since the mid-1970s and that there was no evidence of a net increase in brightness during this period.
Some scientists assert that a warming of the stratosphere, which has not been observed, would be expected if there were a significant increase in solar activity. AR4 asserts with 90% confidence that observed tropospheric warming and stratospheric cooling is due to the combined influences of greenhouse gas increases and stratospheric ozone depletion.http://en.wikipedia.org/wiki/Global_warming#Solar_variation
Explaination for extra snow:
An increase in global temperatures can in turn cause other changes, including a rising sea level and changes in the amount and pattern of precipitation. http://en.wikipedia.org/wiki/Global_warminghttp://www.usgcrp.gov/usgcrp/Library/nationalassessment/images/PrecipVertical.jpghttp://www.unlv.edu/Climate_Change_Research/MGCF/rainchange.gifhttp://thebluestate.typepad.com/my_weblog/images/picchart063006globalwarming2.gifhttp://thebluestate.typepad.com/my_weblog/al_gore/index.html
Even Bush admits there are things we can do about climate change:
Administration Shifts on Global Warming
By Juliet Eilperin
Washington Post Staff Writer
Friday, August 27, 2004; Page A19
A Bush administration report suggests that evidence of global warming has begun to affect animal and plant populations in visible ways, and that rising temperatures in North America are due in part to human activity. http://www.washingtonpost.com/wp-dyn/articles/A37232-2004Aug26.html