Many previous answers:
Humans have quite an impact on the world and the changes within the climate of the world. These changes are due to humans and their carbon footprint. Temperatures have begun to rise and scientists have been studying this intently for the last 10 years. The speed with which melting ice sheets are raising sea levels is uncertain, but the report makes clear that sea levels will rise inexorably over the coming centuries. Snow cover has decreased in most regions, especially in spring. As well, precipitation in tropic areas will decrease, but increase at high latitudes.
“The current warming trend is of particular significance because most of it is very likely human-induced and proceeding at a rate that is unprecedented in the past 1,300 years.”
“This graph, based on the comparison of atmospheric samples contained in ice cores and more recent direct measurements, provides evidence that atmospheric CO2 has increased since the Industrial Revolution. (Source: NOAA)”
From the IPCC Fourth Report, pg. 36:
“Global GHG [greenhouse gas] emissions due to human activities have grown since pre-industrial times, with an increase of 70% between 1970 and 2004.”
From the IPCC Fourth Assesment Report, pg. 37:
“Human activities result in emissions of four long-lived GHGs: CO2, methane (CH4), nitrous oxide (N2O) and halocarbons (a group of gases containing fluorine, chlorine or bromine). Atmospheric concentrations of GHGs increase when emissions are larger than removal processes. Global atmospheric concentrations of CO2, CH4 and N2O have increased markedly as a result of human activities since 1750 and now far exceed pre-industrial values determined from ice cores spanning many thousands of years The atmospheric concentrations of CO2 and CH4 in 2005 exceed by far the natural range over the last 650,000 years. Global increases in CO2 concentrations are due primarily to fossil fuel use, with land-use change providing another significant but smaller contribution. It is very likely that the observed increase in CH4 concentration is predominantly due to agriculture and fossil fuel use. The increase in N2O concentration is primarily due to agriculture.”
The IPCC Fourth Assesment Report has an entire chapter dedicated to the causes of global climate change, examining both the anthropogenic (human) and natural causes. I highly recommend it (linked below).
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