The concentrations of CO2 and methane have increased by 36% and 148% respectively since the mid 1700s

Global warming is the average increase in global temperature of the Earth's surface air and water. Naturally occurring greenhouse gases have had a global warming effect, which has made the earth habitable. There has been significant debate regarding the causes and the results of global warming, but there has been a consensus within the scientific communities that greenhouse gases emitted since the industrial revolution are responsible for most of the observed temperature increases since the middle of the twentieth century. The concentrations of CO2 and methane have increased by 36% and 148% respectively since the mid 1700s ("Recent Climate Change - Atmosphere Changes, Science, Climate Change, U.S. EPA" (HTML). United States Environmental Protection Agency). These levels are considerably higher than at any time during the last 650,000 years, the period for which reliable data has been extracted from ice cores (Neftel, A., E. Moor, H. Oeschger, and B. Stauffer. (1985). "Evidence from polar ice cores for the increase in atmospheric CO2 in the past two centuries". Nature 315:45-47).
Researchers have predicted that global temperature increase will cause sea levels to rise and change the amount and pattern of precipitation, expanding the subtropical deserts and continuing retreat of glaciers, permafrost, and sea ice significantly affecting the Arctic regions. In addition, scientists predict the reduction of the Amazon rainforest and Boreal forests, and extreme weather changes, and species extinctions and reduction of agricultural yields (Lu, Jian; Gabriel A. Vecchi, Thomas Reichler (2007). "Expansion of the Hadley cell under global warming". Geophysical Research Letters 34: L06805. doi:10.1029/2006GL028443. http://www.atmos.berkeley.edu/~jchiang/Class/Spr07/Geog257/Week10/Lu_Hadley06.pdf.).

Burning of fossil fuels has produced approximately three quarters of the increase in CO2 from human activity. Public awareness of the threat of climate change has risen sharply in the last couple of years and an increasing number of businesses, organizations and individuals are looking to minimize their impact on the climate (Making Sense of the Voluntary Carbon Market A comparison of Carbon Offset Standards).
Governments around the world came together and developed a primary international agreement on reducing greenhouse gas emissions called the Kyoto Protocol, an amendment to the UNFCCC negotiated in 1997.
The Protocol now covers more than 160 countries and over 55 percent of global greenhouse gas emissions ("Kyoto Protocol Status of Ratification". United Nations Framework ConventiononClimateChange. http://unfccc.int, Retrieved on 2007-04-27.). In addition to the Kyoto Protocol, a voluntary market was established where particular policy mandates were not implemented. The United States is part of the voluntary market. The Kyoto Protocol to the United Nations Framework Convention on Climate Change (UNFCCC) established a cap-and-trade system that imposes national caps on the greenhouse gas emissions of developed countries that have ratified the Protocol (called Annex B countries). Each participating country is assigned an emissions target and the corresponding number of allowances - called Assigned Amount Units or AAUs. On average, this cap requires participating countries to reduce their emissions 5.2% below their 1990 baseline between 2008 and 2012. Countries must meet their targets within a designated period of time by:
Reducing their won emissions; and/or
Trading emissions allowances with countries that have a surplus of allowances. This ensures that the overall costs of reducing emissions are kept as low as possible; and/or
Meeting their targets by purchasing carbon credits: to further increase cost-effectiveness of emissions reductions, the Kyoto Protocol also established so-called Flexible Mechanisms: the Clean Development Mechanism (CDM) and Joint Implementation (JI).

Individuals and other organizations outside of the government are effectively lowering their own carbon footprints by improving energy efficiency relying on lower emissions products, and changing consumption patterns. Beyond this, Carbon offsets are gaining prominence as a tool to compensate for emissions. By paying someone else to absorb or avoid the release of a ton of CO2 elsewhere, the purchaser of a carbon offset can aim to compensate for or, in principle, "offset" their own emissions. This is possible because climate change is a non-localized problem; greenhouse gases spread evenly throughout the atmosphere, so reducing them anywhere contributes to overall climate protection.